Sarah R Pryke

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: 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: Theory predicts that parents should adjust reproductive investment in a current breeding attempt by considering the relative fitness benefits of current and future reproductive attempts. Empirical tests, however, have proved problematic because of the difficulties in isolating variables that yield clear and predictable fitness returns to individuals and because partner compensation in socially monogamous species is likely to confound individual investment strategies. We test the effect of parental investment by males and females in the color polymorphic Gouldian finch (Erythrura gouldiae), a species with mutual mate choice and high fitness costs when breeding with incompatible partners. Using a within-individual experimental design, in which both males and females were forced to breed with mates of the same (matched) and different (mixed) color morph, we show that females, but not males, increased their provisioning effort when breeding with compatible mates. By crossfostering offspring within and between matched and mixed pairs, we also found that foster offspring reared by matched pairs, with increased female provisioning, were healthier, grew and developed faster, and fledged earlier than offspring reared by mixed pairs. Furthermore, due to the experimental design, these effects were directly mediated by differential investment by females and not by male compensation. Thus, our results provide support for maternal (but not paternal) effects in response to mate quality.

Abstract: The captive zebra finch, Taeniopygia guttata, has become one of the key vertebrate model systems for studying a range of behavioural, physiological and neurological phenomena. In particular, this species has played a key role in developing our understanding of sexual selection and sperm competition. In contrast with the large number of studies using domesticated zebra finches, relatively few studies have focused on free-living populations of wild zebra finches. Investigating the incidence of extrapair paternity in zebra finches in the Australian desert, we found a very low level; 1.7% of 316 offspring from four of 80 broods fathered outside the pair bond. These numbers contrast with the high levels of extrapair paternity observed in domesticated aviary populations, and suggest a low level of sperm competition and sexual selection in natural populations. Our finding of such a low rate of extrapair paternity in the wild zebra finch suggests that it is one of the most genetically monogamous of all passerine species and that has important implications for future studies of this model organism in studies of sexual selection and reproductive biology. In addition, we found that 5.4% of 316 offspring were not related to either putative parent and hatched from eggs that had been dumped by intraspecific brood parasites. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

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: Assortative mating is a key aspect in the speciation process because it is important for both initial divergence and maintenance of distinct species. However, it remains a challenge to explain how assortative mating evolves when diverging populations are undergoing gene flow (e g., during hybridization) Here I experimentally test how assortative mating is maintained with frequent gene flow between diverged head-color morphs of the Gouldian finch (Erythrura gouldiae). Contrary to the predominant view on the development of sexual preferences in birds, cross-fostered offspring did not imprint on the phenotype of their conspecific (red or black morphs) or heterospecific (Bengalese finch) foster parents. Instead, the mating preferences of F-1 and F-2 intermorph-hybrids are consistent with inheritance on the Z chromosomes, which are also the location for genes controlling color expression and the genes causing low fitness of intermorph-hybrids. Genetic associations between color signal and preference loci on the sex chromosomes may prevent recombination from breaking down these associations when the morphs interbreed, helping to maintain assortative mating in the face of gene flow. Although sex linkage of reproductively isolating traits is theoretically expected to promote speciation, social and ecological constraints may enforce frequent interbreeding between the morphs, thus preventing complete reproductive isolation.

Abstract: Red coloration has been associated with dominance and aggression in a number of animals. However, it is unclear whether the increased aggression of red individuals or the avoidance of red opponents is an intrinsic or learnt response. By experimentally controlling for genetic and environmental effects, I tested for innate competitive differences and red-enhanced contest success in sexually immature (uncoloured) red and black head colour morphs of the Gouldian finch, Erythrura gouldiae. Despite juveniles being reared by foster parents of the same and different colour morphs, there were no differences in competitive abilities between uncoloured red and black males. However, when I experimentally added a red head mask to uncoloured males, red (but not black and novel blue coloration) was associated with winning contests, irrespective of an individual's underlying genetics or postindependence social experience. In addition, uncoloured opponents expressed higher stress responses (corticosterone) and avoided conflicts with red-painted competitors. The association between red coloration and aggression may be an innate response to aid facultative fight or submissive decisions, and adds to growing evidence suggesting that red coloration may be a general signal of intimidation. (C) 2009 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

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: 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: 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: 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: Sexual selection and species recognition both play important roles in mate choice. Typically, females use the relative expression of male sexual traits to select high-quality or attractive mates (sexual selection) of the same species (species recognition). However, when the variation in male trait expression of both conspecifics and heterospecifics overlaps, females potentially face a conflict between sexual selection and mate recognition. Among the highly polygynous and closely related African Euplectes species (widowbirds and bishops), females show a general and open-ended mate preference for extreme male tail length (even in relatively short-tailed species). To evaluate the relative strength and interaction of directional versus stabilizing selection pressures on tail length, we experimentally examined female mating preferences in the red bishop (Euplectes orix), a short-tailed (4 cm) species sympatric with longer tailed widowbirds (tails 7-50 cm). In standardized mate-choice experiments, females preferred naturally long-tailed males (5 cm), were indifferent to controls (4 cm), but discriminated against short-tailed (3 cm) and supernormal-tailed (8 cm) males. Although the naturally small variation in tail length (5%) is unlikely to function as a primary mate-choice cue, these results suggest a generalized female bias for longer tails (within the natural range). However, directional preferences for longer tails may be constrained by selection pressures to avoid heterospecific mating with the closely related and sympatric longer tailed widowbirds.

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: Although the evolution of genetic color polymorphisms has received much theoretical interest, few empirical studies have investigated the adaptive function of alternative color morphs. Furthermore, most studies have focused almost exclusively on the evolution and adaptive expression of male coloration, leaving the role of conspicuous female coloration largely unknown. Using the color polymorphic Gouldian finch (Erythrura gouldiae), this study experimentally tests the status signaling function of head color (red, yellow, and black) among the 3 female color morphs. In standardized dominance contests between unfamiliar females of different head colors, red-headed females dominated both black- and yellow-headed females. During contests between the morphs, red-headed females passively displaced black- and yellow-headed opponents, whereas interactions between red-headed dyads were particularly aggressive and more frequent than interactions within dyads of the other color morphs. This effect of red dominance further persisted when head color was experimentally altered; red-manipulated females (of the other morphs) dominated both black- and yellow-headed females, whereas blackened red-headed females were dominated by naturally red-headed birds. Together with similar dominance-related differences among male morphs, these results suggest that the 3 color morphs may display alternative strategies in dominance behavior.

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: 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: 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 black nuptial plumage of the highly polygynous male red-collared widowbird (Euplectes ardens) comprises a red carotenoid-based collar patch and a long graduated tail (c. 22 em). Tail length was the strongest predictor of male mating success in a previous selection analysis, motivating this experimental test of the relative importance of tail plumes in male contest competition and female choice. Males were assigned to either a short (12.5 cm) or control (20 cm) tail manipulation prior to territory establishment. Male contest competition was unaffected by the tail treatments as the shortened- and control-tailed males were equally successful in acquiring territories of similar size and quality. In contrast, however, although the longer-tailed control males spent less time in flight and courtship displays, they attracted significantly more prospecting and nearly three times as many nesting females to their territories compared to the short-tailed males. In further support of tail length as the primary mate choice cue, none of the other measured and potential female cues (e.g. body size, collar colorimetrics, territorial behaviours or territory quality) influenced male reproductive success. In addition to potentially increasing detectability ('signal efficacy'), the long tail is also a likely indicator of male quality ('signal content'). Despite the higher activities of short-tailed males, control-tailed males showed a steeper decline in condition (relative body mass) during the breeding season. Furthermore, both short- and control-tailed residents lost more condition than did the short- and control-treated floaters (males not establishing territories), suggesting an interaction between tail length and the costs of territory acquisition, defence and courtship displays. These results confirm the role of mate choice and honest quality advertising as the main selection pressures behind elongated tails in widowbirds. (c) 2005 The Linnean Society of London

Abstract: We explored characteristics and patterns of nest distribution, and their putative costs and benefits to breeding females, in polygynous Red-collared Widowbirds (Euplectes ardens). Red-collared Widowbirds differ from most other Euplectes species, in that male nest-building is reduced to simple nest-rings used in courtship; females alone position and build nests in the territories. Females used only 37% of available territory area for nesting and aggregated at the centers of territories, possibly to take advantage of male vigilance from prominent central perches or to avoid harassment by neighbors. However, irrespective of territory size or number of females on the territory, females maintained relatively even spacing, with nests similar to15 m apart. Nest predation rates were higher (28.2% day(-1)) during the nestling period than during incubation (14.6%), but independent of the number of actively nesting females on a territory. During synchronous nestling stages, however, birds nesting close to other birds incurred higher predation costs. Females may; therefore, centrally clump their nests on a territory but maintain enough distance between nests to reduce nest predation. Females choosing unmated males (monogamous) received no greater costs or benefits than females settling with mated males (polygynous). Taken with our earlier finding of strong female preference for longer-tailed males (Pryke et al. 2001a), our results here suggest that females may gain indirect genetic benefits of higher-quality offspring without incurring the high costs of sharing territories. Received 20 August 2003, accepted 24 June 2004.

Abstract: In breeding plumage, the African male red-shouldered widowbirds (Euplectes axillaris) are black except for red carotenoid-based epaulets ('shoulder patches'), similar to the well-studied American red-winged blackbirds (Agelailis phoeniceus). To experimentally test the signal function of the red epaulets in male red-shouldered widowbirds, we manipulated epaulet colour and size (within natural variation), and observed the effects in two competitive contexts. First, in captivity, unfamiliar males with epaulets of different size or redness were staged in dyadic contests over food. Only epaulet manipulations significantly affected contest outcome; red epaulet males out-competed orange and control males, which in turn dominated blackened (no epaulet) males. Epaulet size manipulations had particularly strong effects; enlarged epaulet males vigorously defeated smaller epaulet males within colour treatments, whereas the independent effect of 'redness' (i.e., within size treatments) was much weaker. Second, in a field experiment, epaulets were manipulated prior to territory establishment. Males with enlarged epaulets acquired territories, whereas most males with blackened or reduced signals failed to obtain territories. Furthermore, among the territorial males, birds with enlarged epaulets defended larger territories and spent less time in boundary signalling, yet they received fewer intrusions from conspecifics. In contrast, epaulet manipulations had no effect on either female visitation rates or subsequent female settlement. These results concur with recent studies and suggest that the carotenoid-based epaulets of red-shouldered widowbirds are status signals, sexually selected through male contest competition for territories.

Abstract: Retention of interconnected, remnant grassland linkages is proposed here to reduce the adverse effects of alien pine afforestation in Afromontane grasslands. Adult butterflies were sampled at 38 grassland sites, representing increasing levels of disturbance both within the afforested area and outside it. Butterfly species richness and abundance in the lesser disturbed grassland remnants within the afforested area were similar to those of the surrounding natural grasslands. In contrast, butterfly species richness, but not necessarily abundance, decreased significantly in the highly disturbed sites, both in the grassland linkages and outside. Although some highly disturbed sites were relatively rich in species, most were visited by geographically widespread and vagile species. In contrast, wide, relatively undisturbed grassland linkages, as well as grasslands outside, were important for localised, sedentary and local endemic butterfly species. Nectar plants, especially the alien Verbena bonariensis, were the most significant variable explaining local butterfly distribution. In addition, tall grasses, hills, topographical landmarks, thermoregulatory sites, shelter and water features were also vital for particular species. It did not matter how deep the grassland linkages were situated inside the afforested area, as long as they were made up of good habitat. Retention of wide, quality grassland linkages are a way forward to maximise biodiversity alongside agroforestry.

Abstract: Many birds display carotenoid-based ornaments, which are typically considered to be honest indicators of individual health and condition. Experimental work on male red-shouldered widowbirds, Euplectes axillaris, has demonstrated a function of the carotenoid-based epaulettes in male contests and territory acquisition. Using two experiments, we investigated whether the natural variation in this colour signal reveals male competitive ability. Males with larger and redder (more longwave) epaulettes established territories to the exclusion of males with smaller and less red signals, which formed a large population of 'floaters'. In an experiment in which we removed 42 resident males, these floaters rapidly filled up vacant territories. Among removed birds held in captivity, residents strongly dominated floaters in dyadic contests over access to an easily monopolized feeder (i.e. outside the context of territory defence). Only epaulette size predicted the outcome of these male contests. In addition, when competitors were experimentally given similar epaulette signals (removed or painted red to the average population size), the males were involved in more aggressive interactions than during unmanipulated contests, but residents continued to outcompete floaters. On release (after 8 days) to the breeding grounds, most residents (88%) rapidly reclaimed their territories from replacements. Combined, these results suggest that some intrinsic 'resource-holding potential', associated with the variation in epaulette signal, is primarily responsible for residents dominating nonresidents. (C) 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.

Abstract: Tail elongation in the polygynous widowbirds (Euplectes spp.) has evoked both adaptive and non-adaptive explanations. Female choice has been shown in the three longest tailed species (20-50 cm), whereas an agonistic function was proposed for a medium-tailed (10 cm) widowbird. To test the generality and directionality of sexual selection on tail length in widowbirds, we experimentally investigated selection in the relatively short-tailed (7 cm) red-shouldered widowbirds (E. axillaris). Prior to territory establishment, males were assigned to four tail-treatment groups; control, short, long and supernormal (similar to a sympatric long-tailed congener). No effects on male competition were detected as the groups were equally successful in acquiring territories of similar size and quality. However, mating success among the 92 territorial males was strongly skewed in favour of supernormal-tailed males (62% of active nests. 5.2 +/- 1.3 nests per territory). Long-tailed males also acquired more nests (1.9 +/- 0.7) than control (0.7 +/- 0.5) and short-tailed (0.5 +/- 0.3) males, while the latter two groups did not differ significantly. These results support a general, open-ended female preference for long tails in widowbirds and may represent a receiver bias that arose early in their divergence from the short-tailed weaverbirds (Ploceinae).

Abstract: Carotenoid-based plumage ornaments are typically considered to be sexually selected traits, functioning as honest condition-dependent signals of phenotypic quality, but few studies have addressed the function of carotenoid color variation in male contest competition. Using two experiments, we investigated the status signaling function of the variable (ranging from yellow to red) carotenoid throat patch (collar) in the polygynous, sexually dimorphic red-collared widowbird (Euplectes ardens). First, we tested if the red collar functions as a dominance signal by painting spectrometrically controlled collar patches onto the brown plumage of nonbreeding males and staging dyadic male contests over food resources. Red-collared males dominated orange males, which in turn dominated the control brown and novel blue collars. Red dominance persisted when the collar manipulations were reversed within dyads and also when tested against testosterone implanted males. In the second experiment the collar size and color of breeding males were manipulated in the field before and after territories were established. All males with enlarged red and most with enlarged orange or reduced red collars obtained territories, whereas most males with reduced orange and all with blackened (removed) collars failed to establish or retain territories. In addition, among the territorial males, those with reduced signals defended smaller territories, received more intrusions, and spent more time in aggressive interactions. Redness and, to a lesser extent, size of the carotenoid ornament both seem to independently indicate male dominance status or fighting ability in male contest competition.

Abstract: Sexual displays often involve several different ornamental traits. Yet most indicator models of sexual selection based on a single receiver (usually a choosy female) find that multiple handicap signals should be unstable. Here we study reasons for this contradiction, analyzing signal function, signal content, and trade-offs between signals in the polygynous red-collared widowbird Euplectes ardens. Males have both a long, graduated tail and a red carotenoid collar badge. Territory-holding "residents" have slightly shorter tails than the nonbreeding "floaters," but their carotenoid collars are 40% larger, and they have (on the basis of reflectance spectrometry and objective colorimetry) a 23-nm more long-wave ("redder") hue than floaters. This corroborates experimental evidence that the red collar is selected by male contest competition, whereas female choice is based almost exclusively on male tail length. Tail length is negatively correlated with the carotenoid signal, which together with body size and condition explains 55% of the variation in tail length. The trade-off in tail length and carotenoid investment is steeper among residents, suggesting an interaction with costs of territory defense. We propose that the "multiple receiver hypothesis" can explain the coexistence of multiple handicap signals. Furthermore, the trade-off between signal expressions might contribute to the inverse relation between nuptial tail elongation and coloration in the genus Euplectes (bishops and widowbirds).

Abstract: Although sexual selection through female choice explains exaggerated male ornaments in many species, the evolution of the multicomponent nature of most sexual displays remains poorly understood. Theoretical models suggest that handicap signaling should converge on a single most informative quality indicator, whereas additional signals are more likely to be arbitrary Fisherian traits, amplifiers, or exploitations of receiver psychology. Male nuptial plumage in the highly polygynous red-collared widowbird (Euplectes ardens) comprises two of the commonly advocated quality advertisements (handicaps) in birds: a long graduated tail and red carotenoid coloration. Here we use multivariate selection analysis to investigate female choice in relation to male tail length, color (reflectance) of the collar, other aspects of morphology, ectoparasite load, display rate, and territory quality. The order and total number of active nests obtained are used as measures of male reproductive success. We demonstrate a strong female preference and net sexual selection for long tails, but marginal or no effects of color, morphology, or territory quality. Tail length explained 47% of male reproductive success, an unusually strong fitness effect of natural ornament variation. Fluctuating tail asymmetry was unrelated to tail length, and had no impact on mating success. For the red collar, there was negative net selection on collar area, presumably via its negative relationship with tail length. None of the color variables (hue, chroma, and brightness) had significant selection differentials, but a partial effect (selection gradient) of chroma might represent a color preference when tail length is controlled for. We suggest that the red collar functions in male agonistic interactions, which has been strongly supported by subsequent work. Thus, female choice targets only one handicap, extreme tail elongation, disregarding or even selecting against the carotenoid display. We discuss whether long tails might be better indicators of genetic quality than carotenoid pigmentation. As regards the evolution of multiple ornaments, we propose that multiple handicap signaling is stable not because of multiple messages but because of multiple receivers, in this case females and males.

Abstract: Flight behaviours of 23 butterfly species were mapped to establish the effect of both pine afforestation and different-sized grassland linkages on localised butterfly movements. Blocks of pine trees caused most butterflies to change direction and move away from the pine edge. Only four species crossed the grassland/pine edge, and of these, only two flew farther than 20 m into the pine forest. The adjacent grassland/indigenous forest edge had a higher number of species, but very few of these entered the forest. Movement rates were significantly faster in the narrow and highly-disturbed linkages, than in the wide and open grasslands, with the linkages acting as conduits between the preferred grassland patches. However, only highly vagile and eurytopic species actually entered the narrower grassland linkages. In contrast, the wider linkages hosted a significantly higher species diversity and functioned as habitats per se and not just as movement corridors, with butterflies frequently stopping to nectar, oviposit, drink and sunbask. Knowledge of butterfly responses to different landscape structures has important conservation and management implications. From the results here, it is recommended that, for these butterflies, the natural grassland linkages should be wider than 250 m. (C) 2001 Elsevier Science Ltd. All rights reserved.

Abstract: Carotenoid colour displays are widely assumed to be honest indicators of individual health or quality, primarily in mate attraction. Here we show that sexually dimorphic carotenoid ornamentation functions as an agonistic signal in male red-collared widowbirds, Euplectes ardens. Mounted mate models differing (within natural limits) in the intensity of carotenoid signalling were presented to wild resident males as simulated intruders, perched or made to 'fly' across the territory with the elongated tail folded or keeled. Perched mounts were generally ignored, and stronger aggression towards 'flying' models with a keeled tail (i.e. as in courtship display) than a folded tail suggests the tail display is used to assess the intention of intruding males. Territory owners were less aggressive towards models with intense collar display, suggesting that carotenoid coloration functions as a badge of status in this species. The level of aggressive response was also related to the resident's own badge in that males with larger, redder collars responded more aggressively to the models. In addition, males with a larger collar signal defended larger territories and spent less time in territory defence. Apart from the collar size and 'redness', no other morphological variable predicted the aggressive response of territorial males. Given the previously demonstrated insignificance of the collar in female mate choice, we suggest that the nuptial carotenoid coloration is an honest signal of dominance or fighting ability, sexually selected through male contest competition over territories. (C) 2001 The Association for the Study of Animal Behaviour.