Abstract: Quality differences between offspring sired by the social and by an extra-pair partner are usually assumed to have a genetic basis, reflecting genetic benefits of female extra-pair mate choice. In the zebra finch (Taeniopygia guttata), we identified a colour ornament that is under sexual selection and appears to have a heritable basis. Hence, by engaging in extra-pair copulations with highly ornamented males, females could, in theory, obtain genes for increased offspring attractiveness. Indeed, sons sired by extra-pair partners had larger ornaments, seemingly supporting the genetic benefit hypothesis. Yet, when comparing ornament size of the social and extra-pair partners, there was no difference. Hence, the observed differences most likely had an environmental basis, mediated, for example, via differential maternal investment of resources into the eggs fertilized by extra-pair and social partners. Such maternal effects may (at least partly) be mediated by egg size, which we found to be associated with mean ornament expression in sons. Our results are consistent with the idea that maternal effects can shape sexual selection by altering the genotype-phenotype relationship for ornamentation. They also caution against automatically attributing greater offspring attractiveness or viability to an extra-pair mate's superior genetic quality, as without controlling for differential maternal investment we may significantly overestimate the role of genetic benefits in the evolution of extra-pair mating behaviour.
Abstract: The relative contribution of genetic and environmental factors in determining variation in life-history traits is of central interest to evolutionary biologists, but the physiological mechanisms underlying these traits are still poorly understood. Here we experimentally demonstrate opposing effects of nutritional stress on immune function, endocrine physiology, parental care, and reproduction between red and black head-color morphs of the Gouldian finch (Erythrura gouldiae). Although the body condition of black morphs was largely unaffected by diet manipulation, red birds were highly sensitive to dietary changes, exhibiting considerable within-individual changes in condition and immune function. Consequently, nutritionally stressed red birds delayed breeding, produced smaller broods, and reared fewer and lower-quality foster offspring than black morphs. Differences in offspring quality were largely due to morph-specific differences in parental effort: red morphs reduced parental provisioning, whereas black morphs adaptively elevated their provisioning effort to meet the increased nutritional demands of their foster brood. Nutritionally stressed genetic morphs also exhibited divergent glucocorticoid responses. Black morphs showed reduced corticosterone-binding globulin (CBG) concentrations and increased levels of free corticosterone, whereas red morphs exhibited reduced free corticosterone levels and elevated CBG concentrations. These opposing glucocorticoid responses highlight intrinsic differences in endocrine sensitivities and plasticity between genetic morphs, which may underlie the morph-specific differences in condition, behavior, and reproduction and thus ultimately contribute to the evolution and maintenance of color polymorphism.
Abstract: Natal dispersal is an important life history trait driving variation in individual fitness, and therefore, a proper understanding of the factors underlying dispersal behaviour is critical to many fields including population dynamics, behavioural ecology and conservation biology. However, individual dispersal patterns remain difficult to quantify despite many years of research using direct and indirect methods. Here, we quantify dispersal in a single intensively studied population of the cooperatively breeding chestnut-crowned babbler (Pomatostomus ruficeps) using genetic networks created from the combination of pairwise relatedness data and social networking methods and compare this to dispersal estimates from re-sighting data. This novel approach not only identifies movements between social groups within our study sites but also provides an estimation of immigration rates of individuals originating outside the study site. Both genetic and re-sighting data indicated that dispersal was strongly female biased, but the magnitude of dispersal estimates was much greater using genetic data. This suggests that many previous studies relying on mark-recapture data may have significantly underestimated dispersal. An analysis of spatial genetic structure within the sampled population also supports the idea that females are more dispersive, with females having no structure beyond the bounds of their own social group, while male genetic structure expands for 750 m from their social group. Although the genetic network approach we have used is an excellent tool for visualizing the social and genetic microstructure of social animals and identifying dispersers, our results also indicate the importance of applying them in parallel with behavioural and life history data.
Abstract: The zebra finch is the model species for the study of the evolution of birdsong, female song preferences, song learning and the neural processes underlying song learning and production. Despite this, almost all work to date in these fields has focused on domesticated zebra finches in captivity and remarkably little is known about song preferences, or the reproductive success of males with different songs, in wild populations. In this study we tested, for the first time in a wild zebra finch population, whether a male's song structure predicts his reproductive success. We recorded male songs in a nestbox population. Males from this wild population sang longer songs, with a higher peak frequency, than domesticated males. The number of each male's offspring that survived until day 12 posthatching (a proxy for fledging success) was used as a measure of reproductive success. Nestlings were partially cross-fostered, allowing us to disentangle the indirect effects of male genetic quality or maternal effects from those of direct benefits such as parental care. Male song structure predicted the number of genetic offspring surviving, as well as hatching success, but not the number or size of eggs in a clutch. Song structure did not predict the number of unrelated foster-offspring that survived. These results provide the first evidence that differences in male song can predict differences in reproductive success in the zebra finch, and suggest that differences in genetic quality are responsible, rather than differences in parental care or maternal investment in the eggs. (C) 2011 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Abstract: For cavity-nesting birds, tree cavities often represent a critical, defendable, and limiting resource that is frequently under intense interspecific competition. However, the dynamics of interspecific conflict resolution, especially between species of similar size, are often unclear. We experimentally tested aggression and nest-defense behaviors in Gouldian Finches (Erythrura gouldiae) and Long-tailed Finches (Poephila acuticauda), two sympatric, cavity-nesting estrildid finches that are very similar in size, ecology, and nest-site requirements. Mounted taxiderinic models of conspecific and heterospecific nest-site competitors (black and red Gouldian Finch morph and Long-tailed Finch models), as well as a control noncompetitor (Black-chinned Honeyeater [Melithreptus gularis]), were presented to Gouldian and Long-tailed finches. These two competing species differed in their overall responses to simulated intruders and in their relative aggression toward conspecific and heterospecific intruders. Long-tailed Finches reacted more quickly to models, approached closer, and were more likely to at tack models (i.e., make physical contact) than Gouldian Finches, which suggests that Long-tailed Finches are intrinsically more aggressive. In addition, Long-tailed Finches were more aggressive toward Gouldian Finches than toward conspecific models. By contrast, Gouldian Finches were more aggressive to conspecific models and avoided approaching Long-tailed Finch models. Male Gouldian Finches were particularly aggressive toward conspecifics, and red head-color morphs were more aggressive than black morphs. These results suggest that the outcomes of competitive asymmetries within and between these species are driven by differences in aggression. Together with the substantial overlap in nest-site use, the Long-tailed Finch's aggressive domination of limited nest sites may lead to competitive exclusion of the endangered Gouldian Finch. Received 14 April 2011, accepted 25 May 2011.
Abstract: Female birds have been shown to have a remarkable degree of control over the sex ratio of the offspring they produce. However, it remains poorly understood how these skews are achieved. Female condition, and consequent variation in circulating hormones, provides a plausible mechanistic link between offspring sex biases and the environmental and social stresses commonly invoked to explain adaptive sex allocation, such as diet, territory quality, and body condition. However, although experimental studies have shown that female perception of male phenotype alone can lead to sex ratio biases, it is unknown how partner quality influences female physiological state. Using a controlled within-female experimental design where female Gouldian finches (Erythrura gouldiae) bred with both high- and low-quality males, we found that partner quality directly affects female hormonal status and subsequent fitness. When constrained to breeding with low-quality males, females had highly elevated stress responses (corticosterone levels) and produced adaptive male-biased sex ratios, whereas when they bred with high- quality males, females had low corticosterone levels and produced an equal offspring sex ratio. There was no effect of other maternal hormones (e. g., testosterone) or body condition on offspring sex ratios. Female physiological condition during egg production, and variation in circulating hormones in particular, may provide a general mechanistic route for strategic sex allocation in birds.
Abstract: This article responds to the recent prominence of ornithological literature advocating the plucking or clipping of feathers to obtain DNA in avian studies. We argue that the practise of feather plucking or clipping should be strongly discouraged on both scientific and ethical grounds in the avian literature. Currently, despite claims to the contrary, it is not clear that feather sampling as a source of DNA has lower ethical impacts on birds than blood sampling. In addition, feather samples provide a smaller and less reliable biological resource, significantly jeopardising the short and long-term outcomes that can be gained by the sampling. In contrast, blood collection has been experimentally demonstrated to be relatively safe, subject to operators being skilled and following published guidelines, providing large yields of high quality DNA that facilitates archival storage of samples in a manner that the destructive sampling of feathers cannot.
Abstract: The evolutionary consequences of parent-offspring conflict have received considerable attention, yet the extent to which parent-offspring conflict influences life history traits remains uncertain. In particular, it is unclear whether hatching patterns are parental strategies to manipulate competitive dynamics among offspring, or whether they are instead consequences of physiological or ecological variables affecting the payoffs of adjusting the onset of incubation. Here we describe an experiment in which we manipulated the hatching pattern of wild free-living zebra finches. We examined the consequences of hatching pattern on parental feeding behaviour and sibling competition, with the aim of identifying selective pressures that underlie differing hatching patterns. Increasing hatching asynchrony reduced the overall quantity of food that parents delivered and the equitability of its distribution among nestlings compared with synchronous broods. However, for each unit of food received, the begging intensity of nestlings from asynchronous broods was lower. As a consequence, the growth rate of first-hatched nestlings in asynchronous broods was significantly greater than those in synchronous broods, and there was no significant difference in growth rate between last-hatched nestlings in asynchronous broods and nestlings from synchronous broods, even though they received less food overall. The reduced scramble competition and energy wasted on begging behaviour in asynchronous broods supports the sibling rivalry hypothesis, suggesting an adaptive function for hatching asynchrony in wild zebra finches. (C) 2011 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Abstract: Zebra finches have played a central role in the discovery of a variety of maternal effects over the past decade, with females shown to adjust resource allocation to their eggs in response to variables such as the appearance of their partner, their own condition, and the diet on which they are maintained. In addition to being the focus of some of the most high profile individual studies that have influenced maternal effects research in birds, the multitude of zebra finch studies together provide the most comprehensive set of data to illuminate general patterns and compare different maternally derived variables. Surprisingly, to date, virtually all of this work has focused on captive populations of the zebra finch that have been domesticated for many generations, and which are typically held under relatively constant environmental and dietary conditions. Here we report the first data on resource allocation across the egg laying sequence in a free-living wild population. Reassuringly we find that the patterns that have been found in the majority of studies of domesticated populations with respect to investment across the laying sequence were all present in the wild population. The size and mass of eggs increased through the laying sequence whilst the concentration of carotenoids significantly decreased across the laying sequence. Although there was no significant pattern with respect to testosterone across the laying sequence the first two eggs had a higher level of testosterone than the last few eggs in the clutch, which is also consistent with the findings of earlier studies in captive populations.
Abstract: In socially monogamous animals, mate choice is constrained by the availability of unpaired individuals in the local population. Here, we experimentally investigate the physiological stress endured by a female (the choosy sex) when pairing with a non-preferred social partner. In two experimental contexts, female Gouldian finches (Erythrura gouldiae) socially paired with poor-quality mates had levels of circulating corticosterone that were three to four times higher than those observed in females that were paired with preferred mates. The elevated level of this stress hormone in response to partner quality was observed within 12 h of the experimental introduction and maintained over a period of several weeks. Our findings demonstrate the extent of intra-individual conflict that occurs when individuals are forced to make mate-choice decisions that are not perfectly aligned with mate-choice preferences. The elevated level of corticosterone also suggests a mechanistic route through which females might adaptively manage their responses to intersexual conflict over reproductive investment.
Abstract: Avian plumage colours are some of the most conspicuous sexual ornaments, and yet standardized selection gradients for plumage colour have rarely been quantified. We examined patterns of fecundity selection on plumage colour in blue tits (Cyanistes caeruleus L.). When not accounting for environmental heterogeneity, we detected relatively few cases of selection. We found significant disruptive selection on adult male crown colour and yearling female chest colour and marginally nonsignificant positive linear selection on adult female crown colour. We discovered no new significant selection gradients with canonical rotation of the matrix of nonlinear selection. Next, using a long-term data set, we identified territory-level environmental variables that predicted fecundity to determine whether these variables influenced patterns of plumage selection. The first of these variables, the density of oaks within 50 m of the nest, influenced selection gradients only for yearling males. The second variable, an inverse function of nesting density, interacted with a subset of plumage selection gradients for yearling males and adult females, although the strength and direction of selection did not vary predictably with population density across these analyses. Overall, fecundity selection on plumage colour in blue tits appeared rare and inconsistent among sexes and age classes.
Abstract: Despite decades of research, whether vertebrates can and do adaptively adjust the sex ratio of their offspring is still highly debated. However, this may have resulted from the failure of empirical tests to identify large and predictable fitness returns to females from strategic adjustment. Here, we test the effect of diet quality and maternal condition on facultative sex ratio adjustment in the color polymorphic Gouldian finch (Erythrura gouldiae), a species that exhibits extreme maternal allocation in response to severe and predictable (genetically-determined) fitness costs. On high-quality diets, females produced a relatively equal sex ratio, but over-produced sons in poor dietary conditions. Despite the lack of sexual size dimorphism, nutritionally stressed foster sons were healthier, grew faster, and were more likely to survive than daughters. Although these findings are in line with predictions from sex allocation theory, the extent of adjustment is considerably lower than previously reported for this species. Females therefore have strong facultative control over sex allocation, but the extent of adjustment is likely determined by the relative magnitude of fitness gains and the ability to reliably predict sex-specific benefits from environmental (vs. genetic) variables. These findings may help explain the often inconsistent, weak, or inconclusive empirical evidence for adaptive sex ratio adjustment in vertebrates.
Abstract: 1. Interspecific interference competition for nest-sites among cavity-nesting birds can have important effects on reproductive fitness and the distribution of competing species. 2. We observed interference at nest-sites in free-living populations of the endangered Gouldian finch (Erythrura gouldiae) and sympatric long-tailed finch (Poephila acuticauda), and also experimentally tested the relative strength and effect of interference at nest-sites in captive populations. 3. Levels of competitive interference at nest-sites in the wild were high for Gouldian, but not long-tailed finches, and interference frequency was inversely related to Gouldian finch reproductive success. High levels of interference conferred reduced fledging success but did not affect offspring condition. 4. Captive experiments corroborated the field data, also demonstrating fitness costs of interspecific competition, and that long-tailed finches dominated resources under standardized conditions. 5. Such asymmetrical competition dynamics are likely to constrain reproduction in Gouldian finch populations, potentially affecting recruitment and hindering the recovery of remaining populations of this endangered species.
Abstract: Although the costs of parental care are at the foundations of optimal-parental-investment theory, our understanding of the nature of the underlying costs is limited by the difficulty of measuring variation in foraging effort. We simultaneously measured parental provisioning and foraging behavior in a free-living population of Zebra Finches (Taeniopygia guttata) using an electronic monitoring system. We fitted 145 adults with a passive transponder tag and remotely recorded their visits to nest boxes and feeders continuously over a 2-month period. After validating the accuracy of this monitoring system, we studied how provisioning and foraging activities varied through time (day and breeding cycle) and influenced the benefits (food received by the offspring) and costs (interclutch interval) of parental care. The provisioning rates of wild Zebra Finches were surprisingly low, with an average of only one visit per hour throughout the day. This was significantly lower than those reported for this model species in captivity and for most other passerines in the wild. Nest visitation rate only partially explained the amount of food received by the young, with parental foraging activity, including the minimum distance covered on foraging trips, being better predictors. Parents that sustained higher foraging activity and covered more distance during the first breeding attempt took longer to renest. These results demonstrate that in some species matching foraging activity with offspring provisioning may provide a better estimate of the true investment that individuals commit to a reproductive attempt. Received 3 May 2010, accepted 15 October 2010.
Abstract: Although the zebra finch, Taeniopygia guttata, has been a very important model system for the study of intrafamilial conflict and parental strategies, a detailed understanding of the variation in parental effort that can occur both within and between pairs is lacking. In part this is because many different methods have been used by individual studies to quantify parental care (i.e. nest visit rate, time in the nest and number of feeds per visit), but these have not directly been compared. We used nestbox cameras to monitor parental visit rate and the distribution of food among the nestlings in domestic, captive wild and wild free-living zebra finches. The percentage of nest visits by parents in which they fed the nestlings was consistent, with multiple feeds to different nestlings occurring within a single visit. The quantity of food delivered and its distribution among the nestlings, however, varied greatly both within and between broods. The number of regurgitations a brood received correlated significantly with the number of individual feeds when accounting for environment, but not with nest visit rate or the duration of time parents spent in the nestbox. In captive conditions, parents visited the nest at twice the rate of wild free-living birds, overall providing nestlings with twice the amount of food. Captive conditions also led to food distribution becoming less equitable among the brood, owing to changes in the number of regurgitations per individual feed and the number of overall feeds per nest visit. (C) 2010 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Abstract: The Gouldian Finch (Erythrura gouldiae) has experienced significant decline in population and the extent of its range over the past 40 years, which has generally been attributed to the availability of suitable foraging habitat. Less research, however, has investigated the suitability or availability of breeding habitat of the species. Gouldian Finches are obligate cavity nesters, and a recent study has shown that they select nest-sites non-randomly based on structural characteristics of the cavity. Here we investigated the relative effects of different environmental factors on the spatial distribution of Gouldian Finch nests at two different scales. At the broader, landscape scale (over similar to 60 km(2)), the strongest predictor of nesting density at a site was the abundance of suitable nest-sites. At the finer scale (similar to 1 km(2)), no single factor explained the variation in location of nest-sites. Gouldian Finches require areas of habitat characterised by high densities of suitable nest-sites (tree-cavities). Within these patches, individuals are potentially selecting nest-sites based on the morphometry of cavities rather than landscape features such as topography, vegetation or proximity to water. Our findings should be integrated with studies of feeding and habitat requirements in the non-breeding season, with the aim of constructing holistic and predictive habitat-suitability models for this endangered species.
Abstract: P>1. Interspecific interference competition for nest-sites among cavity-nesting birds can have important effects on reproductive fitness and the distribution of competing species. 2. We observed interference at nest-sites in free-living populations of the endangered Gouldian finch (Erythrura gouldiae) and sympatric long-tailed finch (Poephila acuticauda), and also experimentally tested the relative strength and effect of interference at nest-sites in captive populations. 3. Levels of competitive interference at nest-sites in the wild were high for Gouldian, but not long-tailed finches, and interference frequency was inversely related to Gouldian finch reproductive success. High levels of interference conferred reduced fledging success but did not affect offspring condition. 4. Captive experiments corroborated the field data, also demonstrating fitness costs of interspecific competition, and that long-tailed finches dominated resources under standardized conditions. 5. Such asymmetrical competition dynamics are likely to constrain reproduction in Gouldian finch populations, potentially affecting recruitment and hindering the recovery of remaining populations of this endangered species.
Abstract: We studied the breeding ecology of the Long-tailed Finch (Poephila acuticauda) over three seasons between 2008 and 2010 in the Kimberley region, Western Australia. Breeding took place from February to September, with a peak in laying in March-April. Pairs produced up to three successful broods per season with a mean (+/- s.e.) clutch-size of 4.66 +/- 1.13, mean broods of 3.98 +/- 1.10 young, and an average of 3.87 +/- 1.10 fledged young per successful nest. Nesting failure occurred frequently, with 66.2% of breeding attempts failing to fledge any offspring. In nests where at least one egg hatched (47% of nests), 87 +/- 17% of the eggs hatched. In successful nests, 98 +/- 9% of all nestlings fledged. Annual breeding success was relatively consistent over the three breeding seasons, with 26.8-40.8% of all eggs resulting in fledged young. Successful nesting attempts lasted an average of 39 +/- 3.3 days, with both parents contributing to incubation (duration 13.6 +/- 2.3 days) and brooding and feeding during the nestling period (duration 20.6 +/- 2 days). Site-and mate-fidelity were high, with pairs staying together during and between breeding seasons and 60% of pairs breeding in the same area in a subsequent year.
Abstract: Today, the Zebra Finch is Australia's most studied bird and the focus of intensive multi-million dollar research projects throughout the world. Here we briefly summarise the history of the Zebra Finch in science and document the way in which studies of this species have proliferated and dominated a number of quite different fields within the biological sciences. The importance of the Zebra Finch is likely to increase still further after the recent publication of its genome sequence - only the second bird to be the focus of such an intensive research effort - and providing an amazing resource for understanding this species and genome evolution more generally. Finally, we highlight the contribution made by the late Richard Zann with his studies of the ecology, physiology and behaviour of the wild Zebra Finch and his tremendous enthusiasm for the species. Richard would have welcomed the status that the Zebra Finch currently enjoys in science, and looked forward to the many exciting research opportunities that this supermodel species will continue to provide in the future. 'The Zebra Finch is a small Australian Ploceid which is ideally suitable for laboratory observations. It will nest and rear young in small indoor aviaries. New birds, transported to the laboratory in small boxes, will begin to nest-build and court within minutes of their release into an aviary. There are no seasonal difficulties, as it breeds all through the year. The species is exclusively a seed-eater and the nestlings require no special diet in captivity. The birds are not disturbed by the presence of an unconcealed human observer.' Desmond Morris (1954; Behaviour 6, 271-322).
Abstract: Birds are a particularly good group with which to examine the importance of maternal effects, as parental contributions can be relatively easily quantified compared with other groups. There have undoubtedly been more studies on maternal effects in the Zebra Finch than any other single bird species. Studies of this species have examined the importance of maternal effects mediated through sex allocation, size, nutrients and hormones of of eggs, incubation behaviour and provisioning levels. A synthesis of all of this work illustrates some contrasting results (e.g. many high-profile results have failed to be replicated), some very common patterns (e.g. investment shifts through the laying sequence), and potentially interesting and complex interactions between traits (e.g. between sex of offspring and hormonal profiles of eggs). This extensive collection of work on the Zebra Finch provides useful general insight into the patterns of maternal investment in birds and the effects on offspring phenotype. However, wecaution that the literature is probably littered with studies that have overemphasised the importance of some maternal effects and recent studies have highlighted analytical and logical flaws that have probably led to misplaced confidence in some of the findings reported to date. Finally, it is worth considering that the bulk of the literature is based on studies of captive domesticated birds and ecological and physiological data from individuals in the wild is currently lacking. The biological relevance of maternal effects documented in this model species is therefore unclear.
Abstract: Determining the relative access of a species to critical limiting resources requires knowledge of the spectrum of their resource utilisation ( niche space) and that of potential competitors, and the frequency distribution of resources in the environment. We used this theoretical framework to assess the relative access to nesting sites and the potential for interspecific competition between two sympatric cavity-nesting finches. Gouldian (Erythrura gouldiae) and Long-tailed (Poephila acuticauda) Finches are both estrildid finches with similar ecological requirements, gross morphology and geographical ranges. By measuring the characteristics of all tree-cavities in an area of breeding habitat, and identifying those used by each of the two species, we were able to quantify the relationship between total available variation and variation in use by Gouldian and Long-tailed Finches. Using a likelihood-based method, we found that Long-tailed Finches exhibited a broader niche than Gouldian Finches with respect to available variation, and that these niches overlapped. Using these data we estimated that the effective availability of suitable nesting sites for Long-tailed Finches was 38% greater than for Gouldian Finches. Their relatively specialised niche and overlap with a more generalist competitor has the potential to constrain reproduction for Gouldian Finches, and will have implications for the conservation of remaining populations of this endangered species.
Abstract: Individuals in socially monogamous species may participate in copulations outside of the pair bond, resulting in extra-pair offspring. Although males benefit from such extra-pair behavior if they produce more offspring, the adaptive function of infidelity to females remains elusive. Here we show that female participation in extra-pair copulations, combined with a genetically loaded process of sperm competition, enables female finches to target genes that are optimally compatible with their own to ensure fertility and optimize offspring viability. Such female behavior, along with the postcopulatory processes demonstrated here, may provide an adaptive function of female infidelity in socially monogamous animals.
Abstract: Studies of sexual selection have focused mainly on dimorphic and/or polygynous species, where males, typically possess more exaggerated secondary sexual characters. However in many species, receiving far less attention, the expression of ornamental traits by females matches that in males. Several hypotheses have been proposed to explain sexual monomorphism, including mutual mate choice, genetic correlation, weak sexual selection and sexual indistinguishability. The sexual indistinguishability hypothesis suggests that sexual monomorphism is an adaption to avoid competition in monogamous flock-living species. Based on measurements of museum skins and domesticated birds in Europe, the Australian long-tailed finch was classified as a sexually monomorphic species, providing the best empirical support for the sexual indistinguishability hypothesis. Using both domestic and wild long-tailed finches, we have re-evaluated the extent to which the sexes are really indistinguishable. Morphological measurements of wing, tail, tail streamers, tarsus, bill and patch size, and colour spectrometric measurements of the yellow upper mandible and grey crown, were compared between the sexes. While the sexes are similar, males and females nonetheless differed in seven of ten traits in wild populations. In domestic populations, the sexes differed to a lesser extent but were still significantly different at three of ten traits, and discriminant analysis showed that 92% of wild individuals and 89% of domestic individuals could reliably be sexed based on just these morphological traits. Contrary to previous work, this study demonstrates that wild long-tailed finches are sexually dimorphic, and that the similarity between males and females in this species cannot be explained by the sexual indistinguishability hypothesis.
Abstract: The apostlebird (Struthidea cinerea) is an Australian endemic passerine belonging to the Corcoracidae family. The species is highly gregarious throughout the year and the name of the species refers to the apparent prevalence of social groups of around 12 birds. The species is becoming a model system for the study of sociality in vertebrates, which will require the analysis of relatedness, paternity and maternity. We characterize 12 microsatellite loci tested for polymorphism on 25 individuals from a population in western New South Wales, Australia. The number of alleles ranged from 4 to 9 per locus. Expected heterozygosities ranged from 0.69 to 0.88. This microsatellite panel will facilitate future studies that will advance our understanding of dispersal processes, inbreeding avoidance and reproductive skew in social animals.
Abstract: The Australian zebra finch, Taeniopygia guttata, is a widely used model organism, yet few studies have compared domesticated and wild birds with the aim of examining its relevance as an evolutionary model species. Domestic and wild broods hatch over approximately 4 and 2 days, respectively, which is important given that nestlings can fledge after as little as 12 days, although 16-18 days is common. We aimed to evaluate the extent to which the greater hatching asynchrony in domestic stock may effect reproductive success through greater variance in size hierarchies, variance in within-brood growth rates, and partial brood mortality. Therefore, by simultaneously controlling brood sizes and experimentally manipulating hatching intervals in both domesticated and wild birds, we investigated the consequences of hatching intervals for fledging success and nestling growth patterns, as well as trade-offs. Fledging success was similarly high in domestic and wild broods of either hatching pattern. Nonetheless, between-brood analyses revealed that domestic nestlings had significantly higher masses, larger skeletal characters, and longer wings than their wild counterparts, although wild nestlings had comparable wing lengths at the pre-fledging stage. Moreover, within-brood analyses revealed only negligible differences between domestic and wild nestlings, and larger effects of hatching order and hatching pattern. Therefore, despite significant differences in the hatching intervals, and the ultimate size achieved by nestlings, the domestication process does not appear to have significantly altered nestling growth trade-offs. The present study provides reassuring evidence that studies involving domesticated zebra finches, or other domesticated model organisms, may provide reasonable adaptive explanations in behavioural and evolutionary ecology. (C) 2010 The Linnean Society of London, Biological Journal of the Linnean Society, 2010, 100, 763-773.
Abstract: Bird vocal duets are joint displays where two individuals, generally a mated pair, produce temporally coordinated vocalizations. Duets may contribute to pair bond maintenance, mate guarding or collaborative defence of resources. The degree of coordination between mates and the variety of vocalizations, however, vary considerably. Although only 3-4.3% of bird species have been reported to duet, this may be because studies have generally focused on conspicuous duets, and more private forms of duet might have been overlooked. We investigated private vocal communication between mates in wild zebra finches, Taeniopygia guttata, a gregarious Australian songbird that forms life-long pair bonds. The partners are inseparable unless nest building, incubating or brooding. Using microphones inside nestboxes, we monitored interactive communication between partners at the nest and its variation during different stages of breeding. After periods of separation, partners performed coordinated mutual vocal displays involving specific soft vocal elements that fulfilled all the criteria used to define duets. In addition, using playback experiments, we obtained preliminary results suggesting that these soft calls could allow mate recognition. Thus, we propose that mutual displays at the nest in zebra finches represent private vocal duets and may function to mediate pair bond maintenance. (C) 2010 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Abstract: The widespread use of artificial nestboxes has led to significant advances in our knowledge of the ecology, behaviour and physiology of cavity nesting birds, especially small passerines Nestboxes have made it easier to perform routine monitoring and experimental manipulation of eggs or nestlings, and also repeatedly to capture, identify and manipulate the parents However, when comparing results across study sites the use of nestboxes may also Introduce a potentially significant confounding variable in the form of differences in nestbox design amongst studies, such as their physical dimensions, placement height, and the way in which they are constructed and maintained However, the use of nestboxes may also introduce an unconsidered and potentially significant confounding variable clue to differences in nestbox design amongst studies, such as their physical dimensions, placement height, and the way in which they are constructed and maintained Here we review to what extent the characteristics of artificial nestboxes (e g size, shape, construction material, colour) are documented in the 'methods' sections of publications involving hole-nesting passerine birds using natural or excavated cavities or artificial nestboxes for reproduction and roosting Despite explicit previous recommendations that authors describe in detail the characteristics of the nestboxes used, we found that the description of nestbox characteristics in most recent publications remains poor and insufficient We therefore list the types of descriptive data that should be included in the methods sections of relevant manuscripts and justify this by discussing how variation in nestbox characteristics can affect or confound conclusions from nestbox studies We also propose several recommendations to improve the reliability and usefulness of research based on long-term studies of any secondary hole-nesting species using artificial nestboxes for breeding or roosting.
Abstract: Extra-pair paternity (EPP) is an important component of avian mating systems and can affect avian biodiversity by contributing to isolation between related forms. Over the past three decades, molecular surveys of more than 100 species have revealed EPP to be widespread in socially monogamous birds, significantly increasing the variance in reproductive success among males and helping to drive sexual selection on traits with which it is often associated (e.g. song, ornamental plumage). In the past 7 years many studies have also demonstrated that the distribution of EPP within a population is related to the level of genetic similarity between the parents. Multiple mating combined with sperm competition that follows a genetically loaded raffle model, would provide a route through which females could target compatible genes and act as an effective post-copulatory isolating mechanism between closely related species or forms in sympatry. EPP can result in significant divergence between an observed social mating system and the true underlying genetic mating system of a population or species, and needs to be considered in our attempts to define and understand species or morphs as genetically isolated populations in many cases.
Abstract: Sperm morphometry (i.e., size and shape) and function are important determinants of male reproductive success and are thought to be under stabilizing selection. However, recent studies suggest that sperm morphometry can be a phenotypically plastic trait, which can be adjusted to varying conditions. We tested whether different behavioral strategies in aggression between aggressive red and nonaggressive black males of the color polymorphic Gouldian finch (Erythrura gouldiae) can influence sperm morphometry. We show pronounced within-individual phenotypic plasticity in sperm morphometry of male Gouldian finches in three different social environments. Both red and black males placed in intermediate to high competitive environments (high frequency of red males) increased the relative length of their sperm midpiece. By contrast, red males placed in low to intermediate competitive environments (higher frequency of black males) increased the length of the sperm flagellum. Significant changes in stress and sex steroid hormone levels (in response to the competitive environment) appear to influence sperm traits in red but not in black males, suggesting that changes in hormonal levels are not solely responsible for the observed changes in sperm morphometry. These findings imply that males can adjust sperm morphometry across social environments.
Abstract: The severe abdominal pain associated with acute adnexal torsion causes physical stress, which may precipitate a clinical syndrome of acute cardiomyopathy mimicking myocardial infarction.
Abstract: Colonial breeding occurs in a wide range of taxa, however the advantages promoting its evolution and maintenance remain poorly understood. In many avian species, breeding colonies vary by several orders of magnitude and one approach to investigating the evolution of coloniality has been to examine how potential costs and benefits vary with colony size. Several hypotheses predict that foraging efficiency may improve with colony size, through benefits associated with social foraging and information exchange. However, it is argued that competition for limited food resources will also increase with colony size, potentially reducing foraging success. Here we use a number of measures (brood feeding rates, chick condition and survival, and adult condition) to estimate foraging efficiency in the fairy martin Petrochelidon ariel, across a range of colony sizes in a single season (17 colonies, size range 28-139 pairs). Brood provisioning rates were collected from multiple colonies simultaneously using an electronic monitoring system, controlling for temporal variation in environmental conditions. Provisioning rate was correlated with nestling condition, though we found no clear relationship between provisioning rate and colony size for either male or female parents. However, chicks were generally in worse condition and broods more likely to fail or experience partial loss in larger colonies. Moreover, the average condition of adults declined with colony size. Overall, these findings suggest that foraging efficiency declines with colony size in fairy martins, supporting the increased competition hypothesis. However, other factors, such as an increased ectoparasitise load in large colonies or change in the composition of phenotypes with colony size may have also contributed to these patterns.
Abstract: Extrapair paternity (EPP) is common in many socially monogamous species, influencing patterns of sexual selection and shaping many aspects of reproductive behaviour. However, factors explaining variation in the occurrence of EPP, both within and between populations, remain poorly understood. One ecological factor that has received considerable attention is breeding synchrony, but the proposed mechanisms remain contentious and the findings from the large number of correlational studies have been inconsistent. Mate guarding, a behavioural tactic to limit paternity loss, may be fundamental to any relationship between EPP and breeding synchrony. However, few studies have investigated how guarding behaviour varies with breeding synchrony, and the theoretical predictions are unclear. We examined how mate-guarding intensity in the colonial fairy martin varied with changes in breeding synchrony. To eliminate likely confounding effects of individual quality, we measured guarding intensity on multiple days during the fertile period of individual females and related this to daily variation in colony-level breeding synchrony. Similarly, we examined whether extrapair interest in fertile females varied with change in breeding synchrony. Both mate-guarding intensity and extrapair pursuit rate increased sharply several days prior to egg laying, before declining once laying commenced. When we controlled for this effect of female fertility status, guarding intensity increased with breeding synchrony. These novel findings suggest that the risk of paternity loss increases with breeding synchrony, at least among colonial species. Moreover, adjustment of guarding intensity to the risk of paternity loss may explain why most correlational studies do not reveal a relationship between EPP and breeding synchrony. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Abstract: Individuals often face trade-offs between investment in parental care and alternative investments of time, energy, and resources into other life-history components, such as dominance, attractiveness, and health. Selection is thought to promote the optimal balance between the costs and the benefits of these conflicting activities by favoring individuals that adopt different tactics to maximize their overall evolutionary fitness in different environments. To test this, we experimentally manipulate both aggression (i.e., competitive environment) and parental effort (i.e., brood size) in red and black morphs of the Gouldian finch (Erythrura gouldiae). Although aggressive red males provide parental effort comparable to that of black males in environments where competition is low, irrespective of their relative brood size, they severely reduce or abandon parental investment in highly competitive environments. In contrast, non-aggressive black males are largely unaffected by the competitive environment and instead adaptively adjust their provisioning effort to the relative demands of their brood. Consequently, in highly competitive environments, although dominant red males defend higher-quality nest sites, they produce fewer and lower-quality offspring (in terms of mass and immunocompetence) than black males do. These opposing effects of frequency-dependent competitive environments on red and black males underlie their differential trade-offs between the costs and the benefits of aggression and parental effort.
Abstract: The endangered Gouldian Finch (Erythura gouldiae) possesses a genetic colour polymorphism in the form of three genetically determined head-colours (yellow, black and red) that coexist in the same population. The spatial and temporal pattern of morph ratios within this species provides insight into the selective pressures acting on and maintaining the different forms. To investigate spatial and temporal patterns in the relative historical abundance of the different Gouldian Finch morphs, we surveyed museum collections around the world, identifying 614 wild-caught skins and obtaining accurate data on the morphs of 552 of these. The yellow morph was found at very low numbers ( only 15 skins), consistent with its rarity in contemporary populations. Red- and black-morph individuals were found at relatively constant ratios across the geographical range over which they were sampled, and across the 140-year period during which these skins were collected, although this differed slightly for males and females ( males: 62.6% black, 37.4% red; females: 79.1% black, 20.9% red). Spatial and temporal stability in the frequency of alternative morphs is extremely rare. These results suggest that the genetic architecture underlying the trait and selective pressures acting on the separate morphs of the Gouldian Finch differ between the sexes, but are fairly constant across highly variable environmental conditions.
Abstract: Divergent selection pressures among populations can result not only in significant differentiation in morphology, physiology and behaviour, but also in how these traits are related to each other, thereby driving the processes of local adaptation and speciation. In the Australian zebra finch, we investigated whether domesticated stock, bred in captivity over tens of generations, differ in their response to a life-history manipulation, compared to birds taken directly from the wild. In a 'common aviary' experiment, we thereto experimentally manipulated the environmental conditions experienced by nestlings early in life by means of a brood size manipulation, and subsequently assessed its short- and long-term consequences on growth, ornamentation, immune function and reproduction. As expected, we found that early environmental conditions had a marked effect on both short- and long-term morphological and life-history traits in all birds. However, although there were pronounced differences between wild and domesticated birds with respect to the absolute expression of many of these traits, which are indicative of the different selection pressures wild and domesticated birds were exposed to in the recent past, manipulated rearing conditions affected morphology and ornamentation of wild and domesticated finches in a very similar way. This suggests that despite significant differentiation between wild and domesticated birds, selection has not altered the relationships among traits. Thus, life-history strategies and investment trade-offs may be relatively stable and not easily altered by selection. This is a reassuring finding in the light of the widespread use of domesticated birds in studies of life-history evolution and sexual selection, and suggests that adaptive explanations may be legitimate when referring to captive bird studies.
Abstract: Alternative genetically determined color morphs within a population or species are believed to successfully interbreed within a population. However, the occurrence of prezygotic or ecological selection in a number of polymorphic systems may lead to nonrandom mating and prevent genetic morphs from fully interbreeding. Here we show that postzygotic incompatibility significantly limits gene flow between the sympatric red and black color morphs of the Gouldian finch (Erythrura gouldiae). Using a balanced within-female experimental design, in which individuals were forced to breed in pure and mixed morph crosses, we found large inviability effects (> 30%) in offspring resulting from genetically mixed genotypes. The consistent mortality effects across different stages of development (e.g., prehatching, juvenile, adulthood), unconfounded by environmentally derived parental effects or social environments, reveal an underlying genetic incompatibility between different genotypes. Furthermore, mortality in mixed morph genotypes was particularly severe (43.6%) for the heterogametic sex (daughters), which is consistent with Haldane's rule predicted for postzygotic incompatibilities between hybridizing species. This significant, but incomplete, postzygotic isolation suggests that the sympatric morphs may represent transient stages in the speciation-hybridization process.
Abstract: Most cooperative breeding bird species live in family groups that are formed through the prolonged association of offspring with their parents. Research into cooperative families has in particular investigated the balance between cooperation and conflict over reproductive decisions. As a consequence of this research focus, social interactions among group members outside the breeding season are rarely studied, despite the fact that they are likely to be crucial for social decisions. We investigated the social dynamics and ranging behaviour of the family group living cooperatively breeding apostlebird (Struthidea cinerea) outside the breeding season. Group size changed between, but not within, the seasons, being smaller during the breeding season than in the winter season. This change in group size was a consequence of breeding groups merging after breeding, then splitting again before the next breeding season. While breeding groups used small, non-overlapping home ranges (x = 113 ha) around the nesting site, during winter groups moved up to 1200 ha (x = 598 ha), and interacted frequently with up to four other winter groups. In particular large groups often joined together during winter and spent up to 50% of their time associating with other large winter groups. This apparent fission-fusion system facilitated the exchange of group members, offering the possibility to form new breeding coalitions and new groups. The results of this study suggest that behaviour outside the breeding season can be of considerable importance to the social dynamics of both families and cooperative breeding in such systems.
Abstract: Genetic compatibility may drive individual mate choice decisions because of predictable fitness effects associated with breeding with incompatible partners. In Gouldian finches (Erythrura gouldiae), females paired with genetically incompatible males of alternative color morphs overproduce sons, presumably to reduce investment in inviable daughters. We also observed a reduced overall investment in clutch size, egg size, and care to offspring resulting from incompatible matings. Within-female experimental pairings demonstrate that female birds have the ability to adaptively adjust the sex of their eggs and allocate resources on the basis of partner quality. Female Gouldian finches thus make cumulative strategic allocation decisions to minimize the costs of poor-quality pairings when faced with a genetically incompatible partner.
Abstract: Long-tailed Finches (Poephila acuticauda) breeding in natural cavities and nest-boxes were monitored during the breeding season, between March and September 2008, as part of an ongoing field study near Wyndham, northern Western Australia. Towards the end of the breeding season, two adults and their son, who had fledged 4 months earlier, were observed together over many days feeding nestlings (10-17 days old) produced by the adults in another breeding attempt. This is the first description of cooperative breeding in an Australian estrildid finch. Based on these observations, we do not intend to suggest that the Long-tailed Finch should be considered a cooperatively breeding species, but such data help us to understand the variation that exists with respect to familial relations and parental care and provides a foundation for work addressed at understanding the evolutionary origins of cooperative behaviour in birds.
Abstract: Reproductive success within populations often varies with the timing of breeding, typically declining over the season. This variation is usually attributed to seasonal changes in resource availability and/or differences in the quality or experience of breeders. In colonial species, the timing of breeding may be of particular importance because the costs and benefits of colonial breeding are likely to vary over the season and also with colony size. In this study, we examine the relationship between timing of breeding and reproductive performance (clutch size and nest success) both within and between variable sized colonies (n = 18) of fairy martins, Petrochelidon ariel. In four of these colonies, we also experimentally delayed laying in selected nests to disentangle the effects of laying date and individual quality/experience on reproductive success. Within colonies, later laying birds produced smaller clutches, but only in larger colonies. The general seasonal decline in nest success was also more pronounced in larger colonies. Late laying birds were generally smaller than earlier laying birds, but morphological differences were also related to colony size, suggesting optimal colony size also varies with phenotype. Experimentally delayed clutches were larger than concurrently produced non-delayed clutches, but only in larger colonies. Similarly, delayed clutches were more likely to produce fledglings, particularly later in the season and in larger colonies. We suggest that the reduced performance of late breeding pairs in larger colonies resulted primarily from inexperienced/low quality birds preferring to settle in larger colonies, possibly exacerbated by an increase in the costs of coloniality (e.g., resource depletion and ectoparasite infestations) with date and colony size. These findings highlight the importance of phenotype-related differences in settlement decisions and reproductive performance to an improved understanding of colonial breeding and variation in colony size.
Abstract: An individual's fitness is assumed to be maximised through early dispersal and independent breeding. However, offspring across a diversity of taxonomic groups delay dispersal and remain with at least one of their parents after reaching sexual maturity. Delayed dispersal and resulting family living are expected to arise when constraints exist on independent reproduction and where offspring benefit by remaining philopatric. A first step to elucidating the nature of such constraints and benefits for a given species is to have an understanding of the social organisation and habitat preferences of a species. The present study examined the social organisation, foraging preferences and characteristics of preferred foraging areas during a breeding season in the cooperatively breeding Chestnut-crowned Babbler (Pomatostomus ruficeps). During the study, groups of Babblers bred plurally in breeding units of two to 13 adults that occupied non-exclusive home-ranges averaging 38 ha, with larger groups occupying larger ranges. Babblers spent most of the day foraging, mostly on the ground, and preferred to forage within drainage zones. The preference for such zones probably arose because they offered both greater vegetative cover from aerial predators and biomasses of potential prey. These findings lead to the prediction that the availability of drainage zones within a group's range will influence offspring dispersal decisions in Chestnut-crowned Babblers at the site studied.
Abstract: Despite two decades of research into over one hundred species, the function of extrapair paternity to female birds remains unclear. Recent studies have demonstrated patterns between extrapair paternity and the genetic similarity of females with social partners and extrapair males. We believe that selection on females to gain genetically compatible fathers for their offspring offers a possible general explanation for the function of extrapair paternity. The idea of sexual selection being driven by genetic compatibility is widely considered by workers on other taxa but has been largely ignored by studies of birds. Genetic compatibility could be optimised by females through a behavioural process before copulation or through a postcopulatory process. Postcopulatory processes such as cryptic female choice have been recently demonstrated in birds and would allow female birds to use a 'genetically loaded raffle' to target compatible genes through sperm competition. We discuss the general weaknesses of studies of extrapair paternity to date and suggest a number of avenues for future research that will help to elucidate the function of extrapair paternity and widespread genetic polyandry in birds.
Abstract: A recent study reported the incidence of intraspecific brood parasitism (IBP) in the blue tit, based on differences in pigmentation between eggs within clutches and the appearance of multiple eggs within a nest in a single day. Here we present data from another population of blue tits Cyanistes caeruleus in which we show that such evidence is not necessarily indicative of IBP. As in many other studies of birds, we found that the patterning and degree of pigmentation on eggs is individually highly characteristic of a female. As in the previous study of blue tits, a minority of clutches (about 3% of 904 clutches) contained one, two or three eggs that were distinctly different from the other eggs in the clutch, either in size or patterning, but not both. Molecular genetic analyses of parentage in a sample of these clutches with suspected IBP demonstrated unequivocally that all eggs within each clutch had in fact been laid by a single female, in all cases the social parent. We also found no evidence of IBP from paternity analyses of a sample of 3,529 offspring from 427 broods in this population, adding to previous evidence of the absence of IBP in this species. These findings cast doubt on the utility of purely observational approaches to provide evidence of intraspecific brood parasitism; our study suggests that egg morphology and records of laying patterns are inadequate to enable the identification of IBP.
Abstract: Several studies have found that island populations of passerines exhibit lower levels of extrapair paternity (EPP) than mainland populations. An explanation proposing that lower levels of genetic diversity in isolated populations reduce the indirect genetic benefits of EPP to females has been supported by observational study but not tested experimentally. Here, we present the results of a manipulative study on an island population of house sparrows (Passer domesticus), which previously exhibited a significantly lower frequency of EPP than mainland populations. Fifty adults from a mainland population with significantly more genetic diversity than the island population (across 17 microsatellite loci) were introduced into the island population, and the incidence of EPP was subsequently monitored over 3 breeding seasons. In the year of the introduction, the incidence of EPP rose to approximately the level seen in mainland populations of house sparrows but dropped to an intermediate frequency in the following 2 years. Unexpectedly, parentage assignment showed that in the year of the introduction, all females producing extrapair offspring were native island birds, as were all the extrapair and cuckolded males. These results suggest that EPP in this experimental population was not driven by females trying to maximize the genetic diversity of their offspring.
Abstract: We describe 18 microsatellite markers isolated in the cooperatively breeding chestnut-crowned babbler (Pomatostomus ruficeps). The number of alleles ranged from seven to 16 per locus (mean N-a = 10.4 +/- 0.54 SE) and the expected heterozygosity ranged from 0.732 to 0.889 (mean H-E = 0.836 +/- 0.01 SE). Three of the 18 loci exhibited significant heterozygote deficiency, but the remaining 15 will be used to analyse population genetic structure and the mating system of this highly social species.
Abstract: We present the first quantitative data on the genetic breeding system of a lark (Alaudidae), the Skylark Alauda arvensis. Using a set of eight microsatellite loci isolated in a variety of passerine species, we genotyped 171 offspring from 52 broods of Skylark and detected 35 extra-pair offspring (20%), in 14 different broods (27%). All offspring matched their putative mother, so there was no evidence of intraspecific brood parasitism. Previous non-genetic studies had suggested that the species was predominantly socially monogamous, with only rare occurrences of social polygyny and polyandry, although some behaviours, such as mate guarding, did suggest the possibility of extra-pair copulations. The relatively high level of extra-pair paternity in this species is likely to affect the variation in male reproductive success because extra-pair paternity was non-randomly distributed amongst males, with those with shorter wings more likely to be cuckolded.
Abstract: A growing number of studies highlight the nontransitive properties of ejaculates when they are in competition to fertilize a female's eggs. Increasingly, these studies suggest that postcopulatory processes act as a filter against sperm from closely related males or those with similar genotypes, limiting the deleterious effects of inbreeding on offspring fitness. We investigated the potential for such postcopulatory mechanisms of inbreeding avoidance in the guppy (Poecilia reticulata), a promiscuous livebearing fish. We used artificial insemination as a method of delivering to a female the combined ejaculates from a first cousin (relatedness coefficient r = 0.125) and an unrelated male. This method of sperm delivery controls behavioral processes of pre- and postcopulatory female choice, which can bias paternity toward unrelated males. Our genetic analysis revealed no effect of parental relatedness on paternity outcomes. The observed mean paternity share for related males (0.47) and associated variance did not differ significantly from an expected binomial distribution that assumes no biased use of sperm with respect to relatedness (0.5). Although our data provide no evidence for postcopulatory mechanisms of inbreeding avoidance, the ability of female guppies to influence ejaculate transfer and retention offers an alternative and easily testable mechanism of inbreeding avoidance in this species.
Abstract: Nest-boxes have been used widely and for many decades in Europe and North America to increase avian reproductive success in species management and conservation programs and to increase the amenability and efficiency with which a species can be studied. Here we describe the establishment of a breeding population of Zebra Finches using nest-boxes in semi-arid, far-western New South Wales, over three breeding seasons (2005-07). The nest-boxes were used readily by Zebra Finches, with a total of 572 breeding attempts recorded in this study. After the introduction of nest-boxes, nearly all breeding attempts were made in these artificial cavities. Zebra Finches breeding in natural nests are prone to high levels of nest predation (>60% in previous studies), but such predation was almost completely eliminated with nest-boxes, with <2% of nests being depredated. Not surprisingly, the reproductive success of pairs breeding in nest-boxes (58% of nests successfully fledged at least one young) was significantly higher than in the natural nests monitored at the same sites in a previous year, and by comparison with previous studies of the same species in other localities across Australia. Our study of the Zebra Finch, a laboratory model used throughout the world, shows the effectiveness of artificial nest-boxes at decreasing levels of predation in the wild and increasing the capacity for research.
Abstract: Finding reliable ways of assessing female mate choice is an essential prerequisite to understanding variation in female preferences and its impact on sexual selection. The zebra finch, Taeniopgyia guttata, is a classic avian model species for investigating mate choice and sexual selection, but to date virtually all work has been carried out using domesticated birds, and there are inconsistencies in the findings between studies. We tested three different methods for measuring female preferences in this species using both wild and domesticated birds. The first method was a traditional two-way mate choice chamber, where we measured the time spent with each male. The second method was a no-choice chamber where a single male and female were placed in the same cage for 5 min, such that the pair could physically interact, and the female's sexual response was recorded. The third method was an aviary set-up, comprising eight birds (four males and four females), and we recorded the number of pair-bonding behaviours observed over a 24-h period. In the aviary, we found that birds formed pair bonds almost exclusively with their own type (wild males paired with wild females, and domestic males paired with domestic females). In the two-way choice chamber, this assortative mating preference was only shown by domestic females, and in the no-choice test, only wild females showed this assortative mating preference. We discuss the possible reasons for these differences between mate choice tests and make recommendations for future studies on mate choice. (C) 2007 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Abstract: We characterized 14 polymorphic microsatellite loci in the house sparrow Passer domesticus. Four loci were isolated from house sparrow genomic libraries and 10 loci were identified by testing 100 loci that had been originally isolated in other passerine species. Loci were characterized in 37-54 unrelated sparrows from British and Norwegian populations. Each locus displayed between two and 31 alleles, with the observed heterozygosity ranging between 0.30 and 0.91.
Abstract: During the past 30 years, many species of farmland birds have declined dramatically in numbers in Northern Europe, a trend coinciding with a tremendous intensification of agriculture, although the exact causes of these declines remain unclear. One of the worst affected species is the Tree Sparrow (Passer montanus). We studied two Swedish Tree Sparrow populations during the years 1996-2004 and found that in both populations, almost half of all laid eggs remained unhatched. This led us to investigate whether the eggs failed to hatch because of: (1) eggs not being fertilised or (2) embryo mortality. Our analyses showed that all of the eggs investigated contained sufficient number of sperm for fertilisation and that they also had other visible signs indicating that fertilisation had occurred. Hatching failure was instead shown to result from embryo mortality. Using molecular techniques, we were able to determine that embryo mortality is more likely to affect male embryos than females and that the fledgling sex ratio was consequently highly female biased. The cause of this sex-biased embryo mortality remains unknown, but various potential explanations are discussed.
Abstract: A recent study by Goran Arnqvist and Mark Kirkpatrick in the American Naturalist (165:S26-S37) suggested that female polyandry in birds is not driven by females because quantitative genetic approximations of selection demonstrated that indirect selection for female infidelity is weaker than natural selection against it. Instead, it was argued that extrapair copulations are the result of antagonistic selection on male behavior driving female coercion. While the approach and framework of the study were very good, the conclusions of the study were premature because a number of potential adaptive components of polyandry were unaccounted for, and several critical assumptions are unsupported by the current empirical data. Our understanding of extrapair paternity in birds, and perhaps polyandry in general, will be improved by a better empirical understanding of the direct benefits of fertility assurance and postcopulatory cryptic female choice and the relationship between polyandry and male investment. In addition, we need to develop a greater awareness of the limitations of trying to study behavior by proxy in the molecular laboratory. Together, these challenges and the framework recently presented should improve our understanding of the true function of extrapair paternity in birds.
Abstract: Nestling birds solicit food from their parents with vigorous begging displays, involving posturing, jostling and calling. In some species, such as canaries, begging is especially costly because it causes a trade off against nestling growth. Fitness costs of begging like this are predicted by evolutionary theory because they function to resolve conflicts of interest within the family over the provision of parental investment. However, the mechanism that links these costs with nestling behaviour remains unclear. In the present study, we determine if the relationships between nestling androgen levels, nestling begging intensities and nestling growth rates are consistent with the hypothesis that testosterone is responsible for the trade-off between begging and growth. We test this idea with a correlational study, using fecal androgens as a non-invasive method for assaying nestling androgen levels. Our results show that fecal androgen levels are positively correlated with nestling begging intensity, and reveal marked family differences in each trait. Furthermore, changes in fecal androgen levels between 5 and 8 days after hatching are positively associated with changes in nestling begging intensity, and negatively associated with nestling growth during this time. Although these correlational results support our predictions, we suggest that that experimental manipulations are now required to test the direct or indirect role of testosterone in mediating the trade-off between begging and growth.
Abstract: Mate choice has important evolutionary consequences because it influences assortative mating and the level of genetic variation maintained within populations. In species with genetically determined polymorphisms, nonrandom mate choice may affect the evolutionary stability and maintenance (or loss) of alternative phenotypes. We examined the mating pattern in the colour polymorphic Gouldian finch (Erythrura gouldiae), and the role of mate choice, both female and male, in maintaining the three discrete head colours (black, red and yellow). In both large captive and wild populations, Gouldian finches paired assortatively with respect to head colour. In mate choice trials, females showed a strong preference for mates with the most elaborate sexually dimorphic traits (i.e. more chromatic UV/blue plumage and longer pin-tail feathers), but did not discriminate assortatively. Unexpectedly, however, males were particularly choosy, associating and pairing only with females of their own morph-type. Although female mate choice is generally invoked as the major selective force maintaining conspicuous male colouration in sexually dichromatic species, and is typically thought to drive nonrandom mating, these findings suggest that mutual mate choice and male mate choice in particular, are an important yet neglected component of selection.
Abstract: Evolutionary theory suggests that alternative colour morphs (i.e. genetically controlled phenotypes) may derive similar fitness under frequency-dependent selection. Here we experimentally demonstrate opposing effects of frequency-dependent social environments on plasma hormone levels (testosterone and corticosterone) and immune function between red- and black-headed male morphs of the Gouldian finch (Erythrura gouldiae). Red-headed males are highly sensitive to changes in the social environment, especially towards the relative density of their own aggressive morph, exhibiting high stress responses and immunosuppression in socially competitive environments. In contrast, the non-aggressive black-headed males follow a more passive strategy that appears to buffer them against social stresses. The differential effect of hormones on aggressive behaviour and immune performance reinforces the contrasting behavioural strategies employed by these colour morphs, and highlights the importance of the social environment in determining the individual basis of behavioural and physiological responses.
Abstract: A large number of coloured sexually selected ornamental traits in the animal kingdom are based on carotenoid and melanin pigments. The biochemical differences between these two classes of pigment, together with their different physiological roles, have led to the general belief that there will be a fundamental difference in the way in which they are used in animal signals. Specifically, it has been argued that carotenoid-based colours will have higher levels of condition dependence and that melanin-based traits will be under tighter genetic control. We present a meta-analysis of studies that have experimentally investigated the signalling quality of the two kinds of colour in birds and show that there is no evidence of a difference between them. Furthermore, we show that the available data are currently very limited, both in the number of studies and in the quality of many of the studies that have attempted to examine this question, and we suggest directions for future work. (c) 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Abstract: Sexually selected traits are often hypothesized to signal male condition or quality, though empirical evidence is mixed, and a number of alternative models of sexual selection do not require condition dependence. We examined the relationship between various measures of condition and dawn songs in male blue tits (Cyanistes caeruleus). We detected 6 largely independent measures of variation (i.e., variables) in these songs. None of these variables were related to blue tits' ultraviolet-blue plumage, a demonstrated sexual signal, thus failing to support the redundant signal hypothesis. We found some evidence that the song variables we measured signaled male quality. There were correlations between body size and certain song traits, though neither male age nor male recapture in the subsequent breeding season (apparent local survival) predicted any song variation. We combined our results with published effect sizes comparing blue tit song with male quality variables using meta-analysis and found that a few song measures are correlates of male quality, though as in our field data, neither male age nor survival appeared related to song. Our relatively large sample sizes (> 60), combined with our meta-analytical integration of 89 effect sizes, make the results regarding the signaling value of our measured components of blue tit song robust. These results demonstrate that 1) only certain aspects of signal variation may be condition dependent and 2) even when components of a sexual signal appear correlated with condition in some studies, these signal components may be unrelated or inconsistently related to a variety of condition indices.
Abstract: Qvarnström et al. test whether the preference of female collared flycatchers (Ficedula albicollis) for males with large forehead patches could have evolved as a by-product of selection acting on male patch size. They find that the crucial genetic correlation between female choice and male patch size is not significant, and conclude that preference for large patches must have been shaped directly by selection. However, their use of the patch size of a female's social partner as a measure of choice is incomplete, and will result in low estimates of the potential for direct selection to shape female preference. Their study is therefore unable to resolve the question of how female preference for large forehead patches has evolved.
Abstract: Recent sexual selection studies on the evolution of bird colouration have mainly focused on signals with a high level of condition-dependent variation, with much less attention given to colour traits whose expression is genetically controlled. Here, we experimentally tested the relative importance of a genetic colour polymorphism in determining male dominance in the Gouldian finch (Erythrura gouldiae), a species displaying three completely discrete but naturally co-occurring genetically inherited phenotypes; yellow-, red- (carotenoid) and black-headed (melanin) morphs. First, in staged dominance contests between unfamiliar birds of different head morphs, red-headed males dominated black-headed males, both of which dominated the yellow-headed birds. Second, within morphs, the intensity and size of the strongly ultraviolet-blue collar determined the outcome of these contests, and among the red-headed males, redder males dominated less chromatic birds. Lastly, when the dominance signal of red-headed birds was experimentally destabilized (i.e. blackened or reddened), naturally red-headed morphs continued to dominate both the black-and yellow-headed morphs. Together, these results suggest that intrinsic dominance-related behavioural differences between the three colour morphs, which are likely to influence the relative fitness of each morph, contribute to the complex selective patterns maintaining these three discrete phenotypes in relatively stable frequencies in wild populations.
Abstract: The extent to which two parents are related to each other can strongly influence the fitness of the offspring. Although females should choose mates based on the level of genetic similarity, current evidence suggests that behavioural kin discrimination in birds is limited and may preclude this possibility. We investigated the potential for cryptic sperm selection in the polyandrous, lek-breeding ruff, Philomachus pugnax. In direct sperm competition between two males, the one that fertilized the majority of offspring was most often least genetically similar to the female. This was not due to intrinsic male qualities such as sperm mobility or ejaculate size, because the predictive variable is the genotype of one male relative to that of the female and of the other competing male. This is an extrinsic quality and an individual male may be favoured in one competitive triad (a female and two competing males) but not in another. This finding has implications for the extent to which birds can adaptively optimize outbreeding, even in the absence of the behavioural ability to discriminate genetic similarity and has broad implications for sexual selection in birds, a taxon in which high levels of genetic polyandry are the norm. (c) 2004 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Abstract: Our view of avian mating systems has been revolutionised by the use of molecular tools that have provided evidence supporting theoretical predictions that extrapair paternity (EPP) and intra-specific brood parasitism (IBP) would be widely observed alternative mating strategies in socially monogamous species. Quasi-parasitism (QP) is a third type of alternative mating strategy, where a female lays an egg in another female's nest and that egg is fertilised by the male partner at the parasitised nest. In contrast to both EPP and IBP, QP has been reported in only 12 species to date. We explore reasons for the apparent rarity of QP in birds and conclude that it is only likely to be adaptive in a fairly restrictive set of circumstances. We also review all of the evidence for the occurrence of QP in birds and find that it is far more limited than generally believed, as many apparent examples may be explained by rapid mate--switching or errors in molecular analysis of parentage. We suggest a number of criteria that need to be met for an unequivocal demonstration that QP has actually occurred.
Abstract: 1. In this study we relate variation in lifetime reproductive success (LRS) of male and female house sparrows Passer domesticus to morphological characteristics. 2. Our analyses demonstrated no sex-specific difference in the distribution of LRS. The variance in LRS was influenced mainly by variation in individual annual reproductive success, and to a lesser extent by variation in individual lifespan. 3. Phenotypic traits explained a significant proportion of the variation in LRS in males, but not in females. The effect of male morphology on LRS operated mainly through an effect on the number of recruiting daughters. 4. The size of the patch of black feathers on the chest of males (badge size) and male bill length were both positively associated with LRS. Lifespan and bill length were positively related and reproductive success increased with badge size. In females, number of recruiting daughters was positively related to bill length, body mass and body condition index due to the positive effect of these traits on annual production of daughters. 5. These results indicate that identifying factors causing the large individual variation in LRS, which is likely to be closely related to fitness, will be important to understand microevolutionary processes in this metapopulation, and hence their demographic feedbacks.
Abstract: Sex allocation theory predicts that females should bias the production of offspring towards the sex that will maximize maternal fitness. Here we demonstrate evidence for nonrandom sex allocation by female ruffs (Philomachus pugnax), at both the individual and population level in relation to female condition. At the population level, female condition varies significantly across 3 years and is mirrored by population sex ratio, such that in years when females are in poor condition the population offspring sex ratio is female-biased, while in years when females are in better condition there was little or no bias. In the year when females were in overall poor condition, females in better condition produced more daughters. The same relationship is also revealed by comparing the sex ratios of individual females breeding in two consecutive years in different condition. As the condition of an individual female improves (across years) she tends to produce more female offspring. Although we have shown that, as in other birds, female condition is an important determinant of sex allocation, our results also suggest that such nonrandom allocation does not occur in every year, being particularly strong in a year when females, on average, are in poorer condition. We suggest that our results are consistent with the idea that skewing the sex ratio is likely to carry a cost to females and that it is adaptive only when the fitness differential between sons and daughters is sufficient to outweigh probable costs.
Abstract: Estimates of genetic components are important for our understanding of how individual characteristics are transferred between generations. We show that the level of heritability varies between 0.12 and 0.68 in six morphological traits in house sparrows (Passer domesticus L.) in northern Norway. Positive and negative genetic correlations were present among traits, suggesting evolutionary constraints on the evolution of some of these characters. A sexual difference in the amount of heritable genetic variation was found in tarsus length, wing length, bill depth and body condition index, with generally higher heritability in females. In addition, the structure of the genetic variance-covariance matrix for the traits differed between the sexes. Genetic correlations between males and females for the morphological traits were however large and not significantly different from one, indicating that sex-specific responses to selection will be influenced by intersexual differences in selection differentials. Despite this, some traits had heritability above 0.1 in females, even after conditioning on the additive genetic covariance between sexes and the additive genetic variances in males. Moreover, a meta-analysis indicated that higher heritability in females than in males may be common in birds. Thus, this indicates sexual differences in the genetic architecture of birds. Consequently, as in house sparrows, the evolutionary responses to selection will often be larger in females than males. Hence, our results suggest that sex-specific additive genetic variances and covariances, although ignored in most studies, should be included when making predictions of evolutionary changes from standard quantitative genetic models.
Abstract: We studied the correlations between offspring sex ratio, UV coloration and overwinter survival in a population of blue tits, breeding in Gotland, Sweden, over three consecutive breeding seasons. In 2 of 3 years, we found that females paired to males with relatively brighter UV-coloration produced a greater proportion of sons in their broods, and that this effect was significant with all 3 years combined, despite a significant year by male UV interaction. In addition, we found other correlates of sex ratio (breeding time, female age and clutch size) in some, but not all years, and some of these showed significantly different relationships with sex ratio between years. In both years for which data were available, there were indications that males with relatively brighter UV coloration, and that paired with females that produced male-biased clutches, were more likely to survive to the next year. In addition, we also found that in both males and females, individuals produced similar sex ratios in consecutive years. Because correlations with the sex ratio may be expected to be weak, variation in results between years within the same population may be explained by low statistical power or genuine biological differences. Our results suggest that conclusions about sex ratio variation in birds should be based on multiple years. The correlations that we found in some years of this study are consistent with models of adaptive sex ratio adjustment in response to mate quality. However, careful experimental work is required to provide tests of the assumptions of these models, and should be a priority for future work.
Abstract: The role of genetic variation in determining fitness in natural populations has been enigmatic for decades. Both theoretical and empirical work suggest that additive genetic contributions to fitness variation are small, whereas observations of inbreeding depression suggest that non-additive genetic contributions to fitness can sometimes be large. We analysed associations between genetic variability at a small number of microsatellite loci and fitness in a natural population of the collared flycatcher Ficedula albicollis, and related these to estimates of additive genetic contributions to the same traits. We found strong single-locus associations between an intra-locus measure of variability (d(2)) and variables related to fitness. These heterotic effects were sex-specific, being found only in mates, and variation at this locus explained as much as 11% of the variance in male lifetime reproductive success. The size of the heterotic effect on a trait depended on how closely that trait was related to fitness, and there was a negative relationship between the size of the heterotic effect and the proportion of a trait's variance due to additive genetic variance. One possibility is that the heterosis results from introgression due to hybridization with the closely related pied flycatcher F. hypoleuca. Our results provide evidence that genetic contributions to fitness can be important in outbred populations.
Abstract: Estimates of genetic components are important for our understanding of how individual characteristics are transferred between generations. We show that the level of heritability varies between 0.12 and 0.68 in six morphological traits in house sparrows (Passer domesticus L.) in northern Norway. Positive and negative genetic correlations were present among traits, suggesting evolutionary constraints on the evolution of some of these characters. A sexual difference in the amount of heritable genetic variation was found in tarsus length, wing length, bill depth and body condition index, with generally higher heritability in females. In addition, the structure of the genetic variance-covariance matrix for the traits differed between the sexes. Genetic correlations between males and females for the morphological traits were however large and not significantly different from one, indicating that sex-specific responses to selection will be influenced by intersexual differences in selection differentials. Despite this, some traits had heritability above 0.1 in females, even after conditioning on the additive genetic covariance between sexes and the additive genetic variances in males. Moreover, a meta-analysis indicated that higher heritability in females than in males may be common in birds. Thus, this indicates sexual differences in the genetic architecture of birds. Consequently, as in house sparrows, the evolutionary responses to selection will often be larger in females than males. Hence, our results suggest that sex-specific additive genetic variances and covariances, although ignored in most studies, should be included when making predictions of evolutionary changes from standard quantitative genetic models.
Abstract: Resource allocation from parents to their offspring can be modulated by inter-sexual size dimorphism. High dimorphism promotes differential costs in rearing male and female offspring and unequal competitive ability among siblings. We examined whether any of these types of biases occur in Eurasian kestrels, Falco tinnunculus, in which females are larger than males. We measured begging behaviour of nestlings during the second week after hatching to establish how parents respond to begging signals. In addition, we looked for possible costs of begging as a trading function with T-cell-mediated immune response or growth. Begging display was higher in nests suffering from food shortage. Parents (mothers in 98% of the cases) allocated more food to chicks begging more intensely. Female chicks obtained more food from parents than males, but only in nests in which parents provided the chicks with prey items small enough to be swallowed whole (without dismembering) by the chicks. No difference in begging calls was observed between male and female nestlings. However, female chicks were closer to the parent in non-dismembering nests. Begging display was not associated with T-cell-mediated immunity or growth. Our results show a clear response of food provisioning by parents to begging display of nestlings, and suggest that the advantage of female nestlings in food acquisition was due to their competitive superiority over male sibling nest-mates in scramble competition for monopolizeable prey.
Abstract: The application of molecular genetic techniques has revolutionized our view of avian mating systems. Contrary to prior expectations, birds are only very rarely sexually monogamous, with 'extra-pair offspring' found in approximately 90% of species. Even among socially monogamous species, over 11% of offspring are, on average, the result of extra-pair paternity (EPP). Based on over 150 molecular genetic studies of EPP in birds, we review two topical areas: (i) ecological explanations for interspecific variation in the rate of EPP; and (ii) evidence bearing on the adaptive function of EPP. We highlight the remaining challenges of understanding the relative roles of genes and ecology in determining variation between taxa in the rate of extra paternity, and testing for differences between extra-pair offspring and those sired within-pair.
Abstract: Recent work on wild birds has revealed the importance of sperm competition as a source of sexual selection, but behavioral and paternity studies have previously provided only indirect evidence for mechanisms of sperm competition in wild birds. In a field study of collared flycatchers Ficedula albicollis we used a previously uncharacterized method to determine the frequency and timing of extra-pair inseminations. By counting the number of sperm trapped on the perivitelline layer of eggs, we determined the timing of inseminations and estimated, on a day-to-day basis, the amount of sperm females stored. Our results showed that female collared flycatchers preferentially engaged in extra-pair copulations when mated to an unattractive male with a small white forehead patch. These copulations were timed for the middle part of their fertile period, at least 2 days after the last within-pair insemination. Although the mean number of extra-pair insemination events was only 1.33 per cuckolding female, the ratio between the number of sperm from extra-pair and pair inseminations was at least 5 to 1. Thus a single, well timed extra-pair insemination caused by female behavior could greatly bias fertilization probability in favor of an attractive extra-pair male. Our results suggest a possible behavioral mechanism for female control of sperm competition.
Abstract: Recent studies of blue tits, Parus caeruleus, have found sexual selection and a viability-indicating function of the structural ultraviolet and blue crown plumage, but the reasons for this signal variation are not understood. Furthermore, studies in England and Sweden have yielded somewhat different results (particularly with regard to the spectral position of the reflectance peak). Here we investigate whether the blue tit UV/blue ornament varies with time of year since such variation might be relevant to the signalling function as well as the apparent difference between populations. From 400 blue tits captured at two different localities in Sweden, we found that objective measures of 'hue' (spectral location), 'chroma' (spectral purity) and 'brightness' (spectral intensity), varied substantially with season. Just after moult (October), crown 'hue' is maximally UV-shifted (359 nm for males and 373 nm for females). Thereafter the peak drifts upwards and by the time of nestling feeding (June) male reflectance peaks at 404 nm and female at 413 nm. This change is probably due to feather wear as well as fat and dirt accumulation, which might constitute an additional male quality cue. Our results suggest that it is important to consider plumage age when exploring variation in structural plumage coloration, and that it can largely explain the difference between the British and Swedish studies. (C) 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002,76, 237-245.
Abstract: Recent work on wild birds has revealed the importance of sperm competition as a source of sexual selection, but behavioral and paternity studies have previously provided only indirect evidence for mechanisms of sperm competition in wild birds. in a field study of collared flycatchers Ficedula albicollis we used a previously uncharacterized method to determine the frequency and timing of extra-pair inseminations. By counting the number of sperm trapped on the perivitelline layer of eggs, we determined the timing of inseminations and estimated, on a day-to-day basis, the amount of sperm females stored. Our results showed that female collared flycatchers preferentially engaged in extra-pair copulations when mated to an unattractive male with a small white forehead patch. These copulations were timed for the middle part of their fertile period, at least 2 days after the last within-pair insemination. Although the mean number of extra-pair insemination events was only 1.33 per cuckolding female, the ratio between the number of sperm from extra-pair and pair inseminations was at least 5 to 1. Thus a single, well timed extra-pair insemination caused by female behavior could greatly bias fertilization probability in favor of an attractive extra-pair male. Our results suggest a possible behavioral mechanism for female control of sperm competition.
Abstract: There are numerous studies of between-individual variation in the expression of sexually selected traits, but relatively few of variation within individuals. We investigated within-individual variation, both between and within years, in the size of the sexually selected white forehead patch of the male collared flycatcher, Ficedula albicollis. Patch size was determined from direct measurements of maximum height and width and by image analysis of photographs. Measures obtained by the two methods were highly correlated with each other. Male patch size showed significant repeatability both within and between years, but repeatability was lower for patch width than for patch height. Recent reanalysis of published data suggests that sexual selection acts mostly on the width of the patch rather than the height, suggesting that the component of patch size subject to sexual selection is most plastic. We found that, within individuals, forehead patch width changed in a predictable manner within years, becoming significantly smaller later in the breeding season. This effect was more pronounced in males with an initially larger patch. Patch size also changed predictably between years: males whose parental effort we manipulated experimentally showed corresponding changes in patch size between years, confirming an earlier finding from this population. Our results show that the size of sexually selected traits can vary within individuals, both in response to trade-offs with other life history traits, and also over short timescales. Such variation in the expression of sexually selected traits is important not only for the information it may provide about the processes controlling variation in such traits, but also because failure to account for it will reduce the accuracy of any attempt to quantify-selection on them. (C) 2001 The Association for the Study of Animal Behaviour.
Abstract: Hybridization in natural populations is strongly selected against when hybrid offspring have reduced fitness. Here we show that, paradoxically, pairing with another species may offer the best fitness return for an individual, despite reduced fitness of hybrid offspring. Two mechanisms reduce the costs to female collared flycatchers of pairing with male pied flycatchers. A large proportion of young are sired by conspecific male collared flycatchers through extra-pair copulations, and there is a bias in favour of male offspring (which, unlike females, are fertile) within hybrid pairs. In combination with temporal variation in breeding success, these cost-reducing mechanisms yield quantitative predictions about when female collared flycatchers should accept a male pied flycatcher as a mate; empirical data agree with these predictions. Apparent hybridization may thus represent adaptive mate choice under some circumstances.
Abstract: Sex allocation theory predicts that parents should manipulate brood sex ratio in order to maximise the combined reproductive value of their progeny. Females mating with high quality males should, therefore, be expected to produce brood sex ratios biased towards sons, as male offspring would receive a relatively greater advantage from inheritance of their father's characteristics than would their female siblings. Furthermore, it has been suggested that sex allocation in chicks fathered through extrapair fertilizations should also be biased towards sons. Contrary to these predictions, we found no evidence that the distribution of sex ratios in a sample of 1483 chicks from 154 broods of blue tits (Parus caeruleus) deviated significantly from that of a binomial distribution around an even sex ratio. In addition, we found no significant effect on brood sex ratio of the individual quality of either parent as indicated by their biometrics, feather mite loads, time of breeding, or parental survival. This suggests that females in our population were either unable to manipulate offspring sex allocation or did not do so because selection pressures were not strong enough to produce a significant shift away from random sex allocation. The paternity of 986 chicks from 103 broods was determined using DNA microsatellite typing. Extrapair males sired 115 chicks (11.7%) from 41 broods (39.8%). There was no significant effect of paternity (within-pair versus extrapair) on the sex of individual offspring. We suggest that, in addition to the weakness of selection pressures, the possible mechanisms responsible for the allocation of sex may not be sufficiently accurate to control offspring sex at the level of the individual egg.
Abstract: The Noisy Miner Manorina melanocephala (Meliphagidae) is a cooperatively breeding bird species in which sons often remain on their natal home ranges and help one or both of their parents. In a population of Noisy Miners in SE Queensland, Australia, a molecular technique was used to explore adult and offspring sex ratios. and also hatching sequences. Among the adult population, there were 2.31 males for every female, and roughly 99% of helping was performed by males. At hatching and fledging, the population sex ratio was even, with exactly 57 males and 57 females. However, in 17 out of 18 broods the first egg to hatch was male, First-hatched males were significantly larger and heavier than their sisters just prior to fledging. Through their helping behaviour, large healthy sons could clearly enhance the future reproductive success of parents. and benefit the entire group. Sex-biased hatching sequences could potentially provide cooperatively breeding birds with a subtle and precise way of varying investment in the helping sex.
Abstract: Recent evidence has revealed an apparently high degree of control by female birds over the physiological aspects of their reproduction and offspring sex allocation, consistent with adaptive hypotheses of sex allocation and differential investment in their offspring. In the house sparrow, we investigated possible mechanisms that may be used by females to enhance the fitness returns from a reproductive effort. Using molecular techniques, we demonstrate that house sparrow eggs containing male embryos are significantly larger than those containing female embryos. We also found that male embryos were laid randomly with respect to laying order. We speculate that this sexual dimorphism of eggs is adaptive, because male house sparrows show greater variance in condition-dependent reproductive success than females. More important, the result provides further evidence of the ability of females to detect or control ovulation of either male or female ova and to differentially invest in one sex over the other.
Abstract: Reproductive effort was manipulated in a free-living population of house sparrows (Passer domesticus) to investigate the trade-off between reproductive investment and the expression of a condition-dependent sexually selected ornament. Phenotypic plasticity in the expression of this trait was related to the experimentally manipulated size of the brood reared by a male. Males that invested more in current reproduction subsequently became more attractive to females in this population as they showed a preference for males with smaller badges. This supports the argument that direct benefits are a primary focus for mate choice by females. Trade-offs between reproductive effort and the expression of sexual ornaments are a potentially important source of phenotypic variation in both sexual ornaments and life-history traits.
Abstract: It is commonly assumed that the intensity of sexual selection is lower in island populations. Extrapair paternity (EPP) is widespread within passerine birds and is indicative of sexual selection. A conservative analysis of the levels of EPP in island and equivalent mainland populations of passerines reveals that insular populations are indeed characterized by low levels of EPP. This supports the idea that the intensity of sexual selection is lower on islands. This relationship has previously been predicted, based on the assumption of low levels of genetic variation for fitness in such populations. The evidence from this analysis suggests that this is just one of several nonmutually exclusive hypotheses that may explain the high fidelity of island-living females.
Abstract: Females are known to benefit from male choice in several different ways but the relationship between these benefits has received little attention. The quality of resources provided by males, such as nest sites; and paternal care are often assumed to covary positively. However, because the location of the nest affects the cost of parental care, these two benefits from mate choice can easily be confounded. To investigate the provisioning ability of successful competitors while controlling for differences in territory quality rye removed early-settled pairs of collared flycatchers (Ficedula albicollis) and allowed replacement by later-arriving males or floaters (i.e. 'poor competitors'). A control group of early-settled males (i.e. 'good competitors') had their females removed. Females paired to good competitors enjoyed a significantly higher reproductive success and tended to receive more parental assistance from their mates compared with females mated to poor competitors. Thus, some males seem able not only to compete successfully over resources but also to feed their offspring at a relatively higher rate. An alternative explanation, that poor competitors invested less in offspring quality in response to a lower share of paternity could be rejected. The rate of extra-pair paternity did not differ between the two treatment groups. Our results suggest that male-male competition can sometimes facilitate female choice of superior care-givers. Thus, a female's benefit from choosing a competitive male may not be restricted to the quality of the resource he defends but can also include superior paternal care.
Abstract: Brilliant blue and violet structural colours are common plumage ornaments in birds, but their signalling functions are poorly understood(1). This may be because birds also communicate in ultraviolet (UV-A) wavelengths (320-400 nm)(2-5), invisible to humans, but a strong spectral component of many structural colours(6). From a wild population of blue tits-Parus caeruleus, sexually dimorphic primarily in the ultraviolet(7,8)-we report experimental evidence that females skew the sex ratio of their offspring in response to the ultraviolet plumage ornamentation of their mates. Masking male ultraviolet reflectance reversed a positive correlation between reflectance and brood sex ratio observed in control pairs, demonstrating a causal effect of male ultraviolet ornamentation on offspring sex ratio. Ultraviolet reflectance also predicted male survival to the following breeding season, suggesting that it serves as a viability indicator. When taken together with ecological effects (laying date, nesting area), our experiments reveal that an unexpected amount of control exists over the primary sex ratio in birds, suggesting that chromosomal sex determination may not constrain the sex ratios of multiparous vertebrates.
Abstract: We used a PCR-SSCP assay to sex 288 nestling Corn Buntings Milaria calandra from 113 clutches studied between 1988 and 1990 in the Western Isles, Scotland. In each year the sex ratio was not statistically different from 1:1. Brood sex ratios did not deviate significantly from the binomial distribution when tested by robust randomisation tests. Although the effect was not strong, the proportion of males in broods declined as the breeding season progressed in 1989, although the opposite trend was observed in 1988 and 1990. Overall, we found no effect of year, timing of breeding, levels of polygyny, brood size or female size on brood sex ratios although several terms had significant interactions with year due to the effects of the data collected in 1989. Independently of brood size, the feeding rates of males, females or both combined did not vary in relation to brood sex ratios. However, the proportion of feeds provided by fathers was highest at male-biased broods when brood size was small (1-3 young) but at female-biased broods when brood size was large (4-5 young).
Abstract: Despite the many studies that have investigated the genetic mating system of socially monogamous birds, very little is known about the underlying causes of extra-pair paternity and few studies have attempted to test those hypotheses which have been suggested. This study describes the analysis of the genetic mating system of two populations of the house sparrow (Passer domesticus), and uses the results from four other populations to test existing hypotheses using an intra-specific comparative approach. The parentage analysis was conducted using a combination of published and newly presented microsatellite loci isolated from the house sparrow. One population in Kentucky, U.S.A. was found to contain what may be considered to be a typical level of extra-pair paternity for this species (10.5%, 19/ 185 offspring). The second, a population on the island of Lundy, UK, exhibited a ver) low level (1.3%, 4/305 offspring), significantly lower than that in all the other populations studied so far. The finding of such diverse rates of extra-pair paternity, along with the existing estimates from other populations, has allowed us to test the effects of breeding density and genetic variation on the level of extra-pair paternity. We found no effect of either factor on the frequency of extra-pair paternity in the house sparrow, leaving the cause of this variation open to fresh ideas. (C) 1999 The Linnean Society of London.
Abstract: Models of sexual selection usually assume that variation in the expression of sexual ornaments is determined largely by genetic, rather than environmental, factors(1). However, empirical support for this assumption conies from studies of species with little parental care(1,2), in which the influence of environmental factors may be limited(3,4), and from studies of just two species(5,6) with parental care, in both of which heritability estimates vary hugely between years or populations(7,8). In the remaining studies of species with parental care, it is not known whether resemblance in sexual ornamentation between relatives was due to shared genes or shared patterns of care(3,4,9-15). Here we use cross-fostering experiments in house sparrows, Passer domesticus, to examine the relative roles of these effects. We demonstrate that, although sons resemble their fathers with respect to sexual ornamentation, this resemblance is mainly due to post-hatching environmental effects rather than shared genes. We also show that sons hatching early in the year have the largest ornaments. These results support models that emphasize the importance of environmental sources of variation(16-18), such as direct paternal effects(4,19,20), on the expression of sexual ornaments, and agree with the general observation that sexually selected traits tend to be condition dependent(1). We urge the incorporation of gene-environment interactions into future models of sexual selection.
Abstract: Theories of sexual selection usually assume that female preferences for male ornamental traits are fixed and always likely to favour the largest or most extravagant sexual ornaments. This is not, however, always necessary or likely, particularly in resource-based monogamous systems. Here we show that in a closed population of house sparrows, small-badged males were preferred by females as both social and genetic mates and produced a higher number of viable offspring. Previous studies of other house sparrow populations have shown females to prefer large-badged males. Given the likely trade-offs operating between different male behavioural and morphological traits, we propose that female choice is a flexible adaptive strategy through which females can select those males likely to supply the male-acquired benefits that are locally most important.
