Darrell J Kemp

Abstract: Sexual selection is thought to be opposed by natural selection such that ornamental traits express a balance between these two antagonistic influences. Phenotypic variation among populations may indicate local shifts in this balance, or that different stable 'solutions' are possible, but testing these alternatives presents a major challenge. In the guppy (Poecilia reticulata), a small freshwater fish with male-limited ornamental coloration, these issues can be addressed by transplanting fish among sites of varying predation pressure, thus effectively manipulating the strength and nature of natural selection. Here, we contrast the evolutionary outcome of two such introductions conducted in the Trinidadian El Cedro and Aripo Rivers. We use sophisticated colour appraisal methods that account for full spectrum colour variation and which incorporate the very latest visual sensitivity data for guppies and their predators. Our data indicate that ornamentation evolved along different trajectories: whereas Aripo males evolved more numerous and/or larger orange, black and iridescent markings, El Cedro males only evolved more extensive and brighter iridescence. Examination of the El Cedro experiment also revealed little or no ornamental evolution at the control site over 29 years, which contrasts markedly with the rapid (approx. 2-3 years) changes reported for introduction populations. Finally, whole colour-pattern analysis suggested that the greatest visual difference between El Cedro introduction and control fish would be perceived by the two most salient viewers: guppies and the putatively dangerous predator Crenicichla alta. We discuss whether and how these evolutionary trajectories may result from founder effects, population-specific mate preferences and/or sensory drive.

Abstract: Selection should favour coloration in organisms that is more conspicuous to their own visual system than to those of their predators or prey. We tested this prediction in Dickerson's collared lizard (Crotaphytus dickersonae), a sexually dichromatic desert reptile that preys on insects and smaller lizard species, and which in turn is prey for birds and snakes. We modelled the spectral sensitivities of the lizards and their avian and snake predators, and compared the conspicuousness of the lizards' entire colour patterns with each class of viewers. Almost all comparisons involving females strongly supported our prediction for greater chromatic and brightness conspicuousness against local terrestrial visual backgrounds to their own modelled visual system than to those of avian and snake predators. Males, in contrast, exhibited far fewer cases of greater conspicuousness to their own visual system than to those of their predators. Our own perception of spectral similarity between blue C. dickersonae males and a local nonterrestrial visual background (i.e. the Sea of Cortez) prompted a further investigation. We compared sea (and sky) radiance with dorsum radiance of C. dickersonae males and with males from two distantly-related Crotaphytus collaris populations in which males possess blue bodies. In all three visual models, C. dickersonae males exhibited significantly lower chromatic contrast with the sea (and sky) than did their noncoastal, blue-bodied congeners. Among potential explanations, the blue body coloration that is unique to male C. dickersonae may offset, if only slightly, the cost of visibility to predators (and to prey) through reduced contrast against the extensive, local, nonterrestrial blue backgrounds of the sea and sky. (C) 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 749-765.

Abstract: Exaggerated male-limited coloration is widespread among butterflies, yet convincing demonstrations of intraspecific mating preferences for signal brightness and/or chromaticity are relatively rare in this group. Here, I couple behavioral experiments involving manipulations of ambient light environments and male reflectance patterns with observation of wild mating patterns to investigate visual mating biases in the large grass yellow (Eurema hecabe). Males in this species possess exaggerated, limited-view ultraviolet (UV) iridescence across most of their dorsal wing surface that has putative sexual signaling function. In the first experiment, conducted in small (0.7-m(3)) cages, individuals were significantly less likely to copulate when the UV portion of natural ambient illumination (i.e., 300-400 nm) was strongly reduced. In 2 subsequent experiments, conducted under full-spectrum sunlight in small and large (5 x 6 x 4 m) cages, males with their UV signal artificially dulled by 25% consistently copulated with fewer, and smaller, females than sham-control individuals. Importantly, the manipulated levels of UV brightness in these experiments fall well within the naturally occurring bounds of variation in male UV reflectance. These findings therefore unanimously support the presence of a UV signal-based female bias. In apparent contrast, comparison of 161 in-copula and 188 free-flying males from a high-density field assemblage revealed that copulating males were significantly older and henceforth actually possessed (subtly) less UV bright wings. Copulating male UV brightness was, however, positively related to the size of their mate, which echoes the experimental findings and may represent a signature of mutual mate choice. I discuss these results in light of the full complexities of the butterfly mating system and the potential signaling value of iridescent coloration in butterflies and animals generally.

Abstract: Aerial contest competition has proven to be a challenging phenomenon to interpret in many territorial insects. Because the duels often consist of elaborate and/or high speed ascending maneuvers, the hypothesis that they are settled due to asymmetries in flight performance is intuitively appealing. We evaluated this hypothesis by contrasting differences in known morphological determinants of flight performance between (1) residents vs. non-residents of the territorial wasp, Hemipepsis ustulata and between (2) H. ustulata vs. a non-territorial relative, Pepsis thisbe. In the first contrast, resident male H. ustulata were seen to be larger, and had a tendency for reduced wing loading, but they did not possess greater flight musculature or wing aspect ratios (i.e., more elongated wings) than their non-resident counterparts. In the second contrast, male H. ustulata exhibited clearly greater flight musculature and greater sexual dimorphism in this parameter (males more muscular), and also exhibited a slight tendency for greater wing loading and smaller aspect ratios than males of the patrolling species P. thisbe. Interestingly, although size is linked with territorial success in H. ustulata, males of this species were not larger than male P. thisbe, nor did the former species exhibit greater sexual size dimorphism. These results do not support the hypothesis that the repeated ascending contests of H. ustulata require, and select for, a high acceleration design. However, the observed intraspecific patterns of flight musculature suggest that high acceleration is favored in males of the perching species, perhaps for the ability to intercept passing receptive females.

Abstract: Female mate choice has been shown to provide direct mating benefits in several animal groups. In butterflies, for which there are increasing reports of fine-scale color-based mate choice, the evolutionary benefits that accrue from such mating biases, if any, are largely unknown. We addressed this issue in the butterfly Colias eurytheme, a species in which females choose mates on the basis of iridescent ultraviolet (UV) wing ornamentation and in which males donate reproductively beneficial nuptial gifts. In the first experiment, we assessed the mass of gifts donated to 77 virgin females by males sampled directly from a field encounter site. Despite large variance in the male adult phenotype and ejaculate, no single aspect of dorsal wing coloration, including UV brightness, chroma, or hue, was related to ejaculate mass. There was, however, an interesting interaction between the effects of male body size and copula duration upon ejaculate mass, with size scaling positively with ejaculate mass among males involved in shorter copulations (those lasting < 70 min) but negatively among males in longer copulations. In the second experiment, we assessed the lifetime fecundity, fertility, and longevity of 85 females mated under similar circumstances to free-flying wild males. Although several wing color parameters proved subtly informative in more sophisticated multivariable models, no model predicted more than about 20% of the variation in any single female fitness parameter. The duration of copulation, which ranged from 35 min to over 16 h and which carries putative costs for females, was, again, only very weakly predicted by male wing color parameters (i.e., R-2=0.089). Given the overall minor predictive power of male wing coloration in general and of UV brightness in particular, our results do not strongly support the hypothesis that female C. eurytheme prefer bright UV males to obtain direct benefits or to minimize the costs associated with lengthy copulations.

Abstract: The evolution of exaggerated sexual ornamentation is classically thought to proceed as a compromise between opposing vectors of sexual and natural selection. In colour-based ornamentation, as exhibited by guppies (Poecilia reticulata), heightened trait expression may be beneficial in promoting attractiveness, but costly in terms of predation. Opportunities to reconcile this compromise will exist if there are differences between conspecifics and predators in their sensory systems; in such situations guppies should evolve to exploit the ways in which their ornamentation would appear maximally conspicuous to conspecifics. In the present study, we addressed this hypothesis via a study of geographic variation employing the most sophisticated colour analysis yet attempted for Trinidadian guppies. We made two paired contrasts, one between two Aripo populations that vary in the presence of the potential predator Aequidens pulcher, and another between Quare and Marianne populations that vary in exposure to a predatory prawn, Macrobrachium crenulatum. We predicted that, if ornamentation is constrained by the presence of either predator, then guppy conspicuousness should change most markedly across each of the two paired populations as viewed by that predator. Although disparity analysis of entire colour patterns indicated significant differences in both contrasts, this prediction was most clearly supported for the Marianne/Quare contrast. Marianne fish, which co-exist with prawns, exhibited larger black spots coupled with less extensive, less bright flank iridescence. The brightness reductions are notable because, as the only potential guppy predator with a dedicated ultraviolet (UV) photoreceptor, prawns may detect passing male guppies via their UV-bright blues, violets and 'UV/oranges'. We discuss our findings in light of the additional insights that might be obtained by combining spectral assessments and visual modeling with more traditional methods of colour pattern appraisal. (C) 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 95, 734-747.

Abstract: Theory predicts that traits subject to strong sexual selection should evolve to be more exaggerated and developmentally integrated than nonsexual traits, thus leading to heightened condition dependence. Until recently, however, efforts to evaluate this prediction have suffered from either a purely correlational (nonmanipulative) approach, or from using manipulations of doubtful ecological relevance. Here I address these issues by integrating observation and manipulation to study condition- and sex-related color variation in a butterfly. The focal species, Eurema hecabe (Pieridae), possesses three sexually homologous and morphogenetically discrete dorsal wing color elements-coherently scattered ultraviolet (UV), pteridine yellow, and melaninic black. The UV is most strongly sexually selected, and is also the only color element with restricted distribution across female wings. Condition dependence and sexual dichromatism were pervasive, characterizing all color traits except the melanic black, and acting such that low condition males resembled high condition females. Although female coloration tended to exhibit greater phenotypic variation, size-scaled UV was more variable and condition dependent in males. Importantly, manipulation of larval resources was sufficient to closely reconstruct the extent and patterns of field-observed phenotypic variation in condition, and color trait expression, which implicates larval resource acquisition as a primary driver of condition dependence. These results support theories regarding phenotypic variation in sexually selected traits.

Abstract: Animal courtship rituals are important for species recognition, and a variety of cues might be utilized to recognize conspecific mates. In this paper, we investigate different species-recognition mechanisms between two sympatric butterfly sister species: the wood white (Leptidea sinapis) and Real's wood white (Leptidea reali). We show that males of both species frequently court heterospecific females both under laboratory and field conditions. The long-lasting elaborate courtships impose energetic costs, since the second courtship of males that were introduced to two subsequent conspecific females lasted on average only one fourth as long as the first courtship. In this paper, we demonstrate that premating reproductive isolation is dependent on female unwillingness to accept heterospecific mates. We studied female and male courtship behavior, chemical signaling, and the morphology of the sexually dimorphic antennae, one of the few male traits visible for females during courtship. We found no differences in ultraviolet (UV) reflectance and only small differences in longer wavelengths and brightness, significant between-species differences, but strongly overlapping distributions of male L. sinapis and L. reali antennal morphology and chemical signals and minor differences in courtship behavior. The lack of clear-cut between-species differences further explains the lack of male species recognition, and the overall similarity might have caused the long-lasting elaborate courtships, if females need prolonged male courtships to distinguish between con- and heterospecific suitors.

Abstract: Many of nature's most striking animal colours are iridescent, exhibiting a high degree of spectral purity and strong angular dependence of intensity and hue. Although a growing number of studies have detailed the intricate mechanisms responsible for producing iridescent colours, few attempts have been made to describe their dynamic appearance in ecologically and behaviourally realistic contexts. We suggest that the optical properties unique to iridescent structural colours are important for understanding how they function as signals during behavioural interactions. Using males of the orange sulphur butterfly, Colias eurytheme, which exhibit an iridescent ultraviolet (UV) reflectance on their dorsal wing surfaces, we develop a holistic framework for inferring the appearance of this signal to conspecifics under field conditions that incorporate data on their spectral sensitivity. We show that, during flight, the UV signal is brightest within a wing beat cycle when viewed from directly above the male. Spectral properties of the signal under natural lighting indicate that male wing colour should be readily perceived and distinguished from that of females and from the dark green visual background of UV-absorbing vegetation. Finally, our analyses permit predictions regarding how signal senders and receivers should orientate themselves for maximal transmission and reception of this ultraviolet iridescent signal. (c) 2007 The Linnean Society of London.

Abstract: In sexual selection, multimodal signals elicit mate choice when more than one sensory modality is activated. However, determining the relative use of each signal is difficult because it requires a comprehensive understanding of the mating system and how this system works under natural conditions. We examined the role of structural ultraviolet (UV) reflectance and pheromones in the butterfly Colias eurytheme. Both traits are important in mediating interspecific interactions and pheromones have been implicated in intra-specific mate choice. UV reflectance, which arises from the presence of a multilayer thin-film interference array, has potential as an honest indicator of male condition, viability and/or age. We investigated the relevance of these signal traits to courtship success by releasing virgin females in the path of free-flying males until each female had rejected and accepted at least one male. This design facilitated a within-subjects (females) analysis of mate choice, thus controlling for potentially confounding variation in intrinsic female receptivity. Principal component analysis indicated that variation across males in UV brightness and pheromones was essentially orthogonal. Females preferred younger males (as subjectively adjudged by wing wear), and while age covaried with UV brightness and almost all pheromone descriptors, UV brightness emerged as the best and most general predictor of male mating success. Our results suggest that this trait serves as an important intraspecific sexual signal in C. eurytheme, and they provide the clearest evidence to date regarding the functional relevance of structural coloration to female mate choice in butterflies. We discuss the preferential use of one secondary sexual characteristic (UV reflectance) over another (pheromones) with regard to evolutionary strategies. (c) 2006 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Abstract: Male mating biases may be a widespread feature of animal mating systems but the phenotypic consequences of these biases are often unclear, especially in species for which the operational sex ratio is strongly male-biased. In Colias butterflies, male choice is thought to be one of the factors responsible for maintaining a female-limited genetic color polymorphism, in which female wings appear either yellowish-orange or white (the "alba" variant). Previous studies have indicated that alba females of two montane Colias species mate fewer times during their lifetime, possibly as a partial consequence of this bias. Here we report the results of a field study of male mating behavior and female mating biology in Colias eurytheme, conducted under conditions of high (summer) and low (spring) population densities. Our data show that despite a substantial male bias in approaching alba vs yellowish-orange phenotypes [ratios of 0.08:1 (spring) and 0.28:1 (summer)], alba females did not contain, on average, fewer or smaller spermatophores. Not one of the 308 sampled females was virgin, but females of both phenotypes accumulated spermatophores with age, and tended to carry fewer, larger spermatophores in spring. These data suggest that significantly fewer (or lighter) spermatophores need not be an obligatory or simple consequence of a strong male bias in butterflies. We discuss these findings in light of the known, thermally and density-dependent complexities of alba reproductive biology and of the Colias mating system.

Abstract: Structural colors result from an interaction between light and the fine-scale physical structure of a surface, and are often extremely bright, chromatic, and iridescent. Given that these visual features depend upon the aggregate abundance and architectural precision of photonic structures, structurally colored sexual ornaments seem well placed to indicate a range of mate quality characteristics. We tested this hypothesis by investigating the signaling potential of structural coloration in the sexually dimorphic butterfly Colias eurytheme. Males of this species display iridescent ultraviolet (UV) markings (arising from multilayer thin films)that overlay a broad area of yellowish-orange pigmentation on their dorsal wing surface. Only the structural UV has demonstrated function as a sexual signal; hence we predicted that it should contain more reliable phenotypic and/or genetic quality information, which would be indicated by phenotypic and/or genetically mediated condition dependence. in two split-family breeding experiments we manipulated condition by exposing full siblings to different stressors at two different juvenile life-history stages: (1) reduced larval host-plant quality and (2) transient heat/cold shocks during metamorphosis. Both stressors had profound effects on key developmental and life-history traits. Each stressor also significantly affected male dorsal coloration; thus, the expression of both structural and pigmentary coloration is phenotypically condition dependent. As predicted, the strongest condition dependence was evident in the brightness and angular visibility (i.e., iridescence) of the UV. Characteristics of both the iridescent UV and pigmentary orange also exhibited moderate-high and significant heritability (H-2 similar to h(2) similar to 0.4-0.9). However, genetic and residual variances did not increase under stress; thus, the observed condition dependence was not genetically mediated as predicted if wing color trait signals "good" genes for the ability to either withstand or circumvent developmental stress. The heightened stress sensitivity of the iridescent UV suggests that it offers an informative lifetime indicator of juvenile environments and, henceforth, adult male phenotypic condition, which may be salient to females seeking a highly fertile and/or nutritious male ejaculate.

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Abstract: Hypothesis: Heritability estimates of total nightly signalling time will be equal for a contemporary data set in Austin (Texas) and an earlier data set collected 127 km away in San Antonio (Texas). Organism: Texas field cricket, Gryllus texensis (Gryllidae: Orthoptera). Background: A corpus of work has been done on Gryllus texensis in Austin, Texas with the underlying assumption that heritability values from San Antonio, Texas apply. Methods: Previous study - realized heritability estimated using an artificial selection experiment. Current study - narrow sense heritability estimated using parent-offspring, full-sib/half-sib, and restricted maximum likelihood methods. Results: Heritability of total nightly signalling time was previously computed as 0.50 and 0.53 for the San Antonio crickets. However, heritability of total nightly signalling time in the Austin crickets is estimated at only 0.006 +/- 0.045. In Austin, only a small portion (1.5 +/- 11%) of the genetic variance in total signalling time is additive.

Abstract: Butterflies are among nature's most colourful animals, and provide a living showcase for how extremely bright, chromatic and iridescent coloration can be generated by complex optical mechanisms. The gross characteristics of male butterfly colour patterns are understood to function for species and/or sex recognition, but it is not known whether female mate choice promotes visual exaggeration of this coloration. Here I show that females of the sexually dichromatic species Hypolimnas bolina prefer conspecific males that possess bright iridescent blue/ultraviolet dorsal ornamentation. In separate field and enclosure experiments, using both dramatic and graded wing colour manipulations, I demonstrate that a moderate qualitative reduction in signal brightness and chromaticity has the same consequences as removing the signal entirely. These findings validate a long-held hypothesis, and argue for the importance of intra- versus interspecific selection as the driving force behind the exaggeration of bright, iridescent butterfly colour patterns.

Abstract: In some species of sulphur butterflies (Pieridae: Coliadinae) females as well as males display bright structural reflectance on their dorsal wing surfaces, although comparatively little attention has been paid to this coloration in females. We examined the spectral properties of female dorsal coloration and scale structure in three species of sulphurs for which published images show bright UV reflectance in females: the Neotropical Anteos clorinde and two species of Indo-Australian Eurema, E. hecabe and E. candida. In A. clorinde and E. hecabe, female UV reflectance is iridescent and produced by thin film interference in a system of ridges and lamellae, as it is in conspecific males. Female A. clorinde exhibit the same spatial distribution and chromaticity of UV reflectance as seen in males, but the UV reflectance in female E. hecabe is much smaller in area compared to that of conspecific males and is both less bright and less chromatic than observed in males. In contrast, UV reflectance in E. candida females is diffuse. and arises from a lack of pterin pigments in the wings, which permits a broad-band scattered reflection to be seen. This is the mechanism that is known to produce bright UV reflectance in females of the confamilial whites. Our results highlight the diversity of UV reflectances and underlying mechanisms in sulphurs and suggest multiple evolutionary pathways leading to this diversity in female sulphur butterflies. (c) 2007 Elsevier Ltd. All rights reserved.

Abstract: Male-male competition over territorial ownership suggests that winning is associated with considerable benefits. In the speckled wood butterfly, Pararge aegeria, males fight over sunspot territories on the forest floor; winners gain sole residency of a sunspot, whereas losers patrol the forest in search of females. It is currently not known whether residents experience greater mating success than nonresidents, or whether mating success is contingent on environmental conditions. Here we performed an experiment in which virgin females of P aegeria were allowed to choose between a resident and a nonresident male in a large enclosure containing one territorial sunspot. Resident males achieved approximately twice as many matings as non-residents, primarily because matings were most often preceded by a female being discovered when flying through a sunspot. There was no evidence that territorial residents were more attractive per se, with females seen to reject them as often as nonresidents. Furthermore, in the cases where females were discovered outside of the sunspot, they were just as likely to mate with non-residents as residents. We hypothesize that the proximate advantage of territory ownership is that light conditions in a large sunspot greatly increase the male's ability to detect and intercept passing receptive females.

Abstract: 1. Structural coloration is a striking component of sexual ornamentation, and may function as a signal of mate quality. Although the proximate optical mechanisms are often well defined, we know much less about the morphological basis for intraspecific variation in structural colour. 2. Males of the butterfly Colias eurytheme L. possess a thin-film interference array on their dorsal wing scales that generates a bright and iridescent ultraviolet (UV) signal. This signal is used in mate choice. 3. Using scanning electron microscopy, we investigated the covariance between nano-structural architecture and UV reflectance in samples that were variously subject to either nutrient stress (using a larval host-plant manipulation), or thermal stress (using transient heat and cold shocks during the pupal period). We employed these two stressors to mimic natural stressful processes and to accentuate the variance in UV signal characteristics. 4. Two primary structure-reflectance relationships were apparent. First, UV brightness increased with the density of scale ridges that bear the interference reflectors. Second, the breadth of above-wing angles for viewing the UV covaried with a measure of thin-film angular orientation. These relationships were, however, either limited to, or stronger among, males of the nutrient stress sample. 5. Our results are consistent with a causal effect of developmental stress on nano-structural architecture and henceforth UV reflectance, but also suggest that the proximate basis for signal variation may be intimately linked to the nature of prevailing stressors.

Abstract: Hypothesis: Structural coloration (iridescent ornamentation) should vary more greatly among individuals and with age than pigment coloration. Structural coloration requires nano-scale precision and might thus more honestly signal male age and condition than pigment-based colours. Organism: A natural population of the orange sulphur butterfly, Colias eurytheme. C. eurytheme females prefer young males, choosing them on the basis of an unknown signal. Site: Cultivated alfalfa (Medicago sativa) fields near Avondale, Arizona, August-September 2004. Methods: I randomly sampled 70 'pristine' males and an additional 98 males in five age classes. I then measured key reflectance characteristics (brightness, hue and chroma) of the dorsal structural ultraviolet markings and of the coincident pigmentary yellowish-orange. Conclusions: Consistent with the sexual selection hypothesis, structural reflectance parameters are more phenotypically variable. Structural reflectance also fades more with age. However, the higher phenotypic variance of structural colour renders it a less precise indicator of male age than pigment colour.

Abstract: Although empirical studies of life history effects upon sexually selected phenomena have largely overlooked contest behaviour, recent research suggests that territorial contest participation in butterflies may be mediated by ageing per se. Verbal and mathematical arguments predict lifetime increases in the expression of risky male reproductive behaviours, such as fighting, under a range of ecological conditions. Here we explored the relevance of ageing per se to contest dynamics in two phenologically distinct populations of the speckled wood butterfly, Pararge aegeria. We established 160 experimental like-population contests among naive south Swedish and Madeiran dyads, 112 of which we varied the age difference between combatants by 3-4 d. Although this age asymmetry did not influence contest outcome in either population, we found weak positive covariance between the loser's age and contest duration amongst Madeiran males. This is consistent with a slight lifetime increase in aggression because the duration of these aerial persistence contests is a sensitive measure of the losing male's level of aggressive intent. However, the size of this effect (semi-partial correlation = 0.281) suggests age is not as strongly relevant to contest behaviour in P. aegeria as in other territorial butterflies. We discuss the ways in which ecological differences between butterfly species, particularly with respect to predation risk, may have influenced the evolution of lifetime aggressive strategies in this group.

Abstract: Although contemporary animal contest theory emphasises the importance of physical asymmetries in resolving disputes, such asymmetries do not obviously settle fights in all groups. Territorial male butterflies, for example, compete via elaborate non-contact aerial interactions in which success is determined by relative persistence. Prior research suggests that the resolution of these contests is not clearly related to physical variables such as body size or energy reserves. However, given that the contests involve elaborate aerial manoeuvres, one long-standing suggestion is that asymmetries in flight performance, and thus flight morphology, may be important. We addressed this hypothesis via a manipulative investigation into the biophysical correlates of contest success in the speckled wood butterfly, Pararge aegeria. This species possesses the ability for significant adaptive phenotypic plasticity in relevant flight morphological parameters. We took advantage of this plasticity to rear 90 individuals of markedly varying flight morphologies, which we then pitted against each other in a semi-controlled experimental fashion. Multiple logistic and lognormal analyses provided little evidence for the relevance of morphological parameters, including relative flight musculature, wing loading and wing aspect ratio (wing length relative to area), to the outcome and/or duration of experimental contests. Instead, we found a positive effect of age upon contest success. Given that ability for high acceleration is strongly linked to variation in these morphological parameters, our findings suggest that flight performance is not a strong determinant of resource-holding potential in this notably territorial butterfly.

Abstract: Large males of the tarantula hawk wasp Hemipepsis ustulata appear to have an advantage in the competition for mates. Large males are more likely to acquire perch territories used to scan for incoming receptive females and territorial males appear more likely to mate than non-territorial males. In addition, among the males that do secure a mate, those that intercept a female on a territory are larger than those that do so elsewhere. Despite the mating advantages apparently enjoyed by larger males of this species, average male size has remained essentially constant over the last 25 yr. Moreover, larger males are not seen to employ certain competitive tactics that might otherwise enhance their reproductive success. Thus, larger males did not preferentially visit the most popular landmark territory compared to a site that attracted fewer visitors overall. Nor were larger males more likely to return to potential territories after marking, capture, and release, either immediately or on a subsequent day. Finally, although large males made up a significantly greater proportion of the males captured at two territories as the 2005 flight season progressed, over all the years of the study, receptive females have not been concentrated in the latter part of the flight seasons.

Abstract: In aerial conflicts among territorial insects, injury costs are not obviously high and contestants cannot physically 'force the issue'. Resource-holding potential in these cases usually relates to morphological and/or biophysical determinants of flight performance and endurance rather than traditional parameters such as size and strength. However, success is sometimes related to body size. Males of the landmark-defending wasp Hemipepsis ustulata compete via elaborate noncontact aerial duels in which large individuals enjoy an advantage. We evaluated the hypothesis that size is important because of a correlation with high-performance flight. We used a residency manipulation to establish 92 escalated contests in which some individuals had the outer 16-18% of their forewings removed to reduce flight performance (independently of body size). Initial residents won most (78%) contests, but logistic analysis indicated that no other parameter, including size, wing treatment and age, could explain the pattern of contest outcome. Survival regression analysis implicated size, age and site location, but not wing treatment, as significant predictors of nonresident contest persistence. We also found evidence of assessment of relative body size. Since our wing treatment had no measurable effect, the importance of body size does not appear as an emergent property of a system in which contest ability is determined primarily by flight performance dynamics. We conclude that aerial contests in H. ustulata are mediated by complex multicomponent decision rules, in which contest role, relative body size, age and perception of resource value collectively determine a contestant's persistence time. (c) 2005 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Abstract: Ultraviolet (UV) colour patterns, particularly those deriving from surface structures, serve a role in sexual signalling and mate choice in a range of animal groups. In the butterfly Colias eurytheme (Pieridae), male-limited iridescent UV functions in species recognition, and has potential as an intraspecific sexual signal of mate quality. I compared the dorsal colouration and body size of males discovered 'in-copula' (N = 95) with a random sample of free-flying individuals (N = 129), both collected from a high density agricultural population located in Chandler, U.S.A. Despite reasonable variance in each trait, I found no among-group differences in UV characters (brightness, hue and angular visibility) or in the coincident pigmentary yellowish-orange (brightness and saturation). Statistical power was sufficient to detect all but the smallest among-group differences, and there was a marginally significant tendency for in-copula males to be larger. These data do not support the hypothesis for intraspecific female choice upon male dorsal colouration. However, I discuss how the density and apparently very young age of individuals in the sampling population may have pre-disposed this result, and thus, how sexual selection on male colouration may operate in a density dependent manner.

Abstract: Males of the tachinid fly Leschenaultia adusta perch on small trees and shrubs on the highest parts of Usery Peak in central Arizona. Individuals select twig perches on the downwind side of these plants and fly out spontaneously from time to time or in response to another passing insect. Conspecific males elicit chases that on occasion escalate into elaborate, high-speed pursuit flights that go back and forth near the plant for several minutes. Although several males sometimes perch together briefly in the same plant, typically only one individual remains at a site for more than an hour on any given day. These site-faithful males can be considered territorial residents; they constituted about one-quarter of the males marked during the study. More than half of these residents returned to the same perch plant for two or more days. Perch plants varied in their attractiveness to male flies; male preferences were largely consistent across two years of study. Given that females were occasionally observed mating at male-occupied plants, we place the mating system of L. adusta within the hilltopping territorial category in which males compete for landmark perching sites attractive to receptive females. As is trite for other hilltopping insects, receptive females of L. adusta appear to be rare and widely distributed.

Abstract: Physical prowess, a key determinant of fight outcomes, is contingent on whole-organism performance traits. The advertisement of performance, via display, is poorly understood because it is unclear how information about performance is encoded into display characteristics. Previous studies have shown that weapon performance (i.e., bite force) predicts dominance and reproductive success in male lizards. We tested the hypothesis that gaping displays by adult male collared lizards (Crotaphytus) can provide an index of weapon performance by exposing the major jaw-adductor muscle complex and that white patches at the mouth corners amplify this index. For territorial adult males, the breadth of the muscle complex, which is not correlated with body size, was a strong predictor of bite force. For nonterritorial yearling males and females, however, measures of body and head size predicted bite force. The patches are highly conspicuous, exhibit UV-reflecting properties within the visual range of lizards, and provide size-independent information about bite force only in adult males. We conclude that exposure of the muscle complex during gaping displays can provide rival males with a reliable, body-size independent, biomechanically based index of weapon performance, an index that the mouth-corner patches amplify. Indexes that transmit information through mechanistic links to performance are expected to be widespread among animals.

Abstract: Many butterflies exhibit structurally coloured wing patches that are stunningly bright and iridescent in their appearance, yet functionally obscure. These colours are often exaggerated in males, which suggests a sexually selected origin. We studied the visual properties, morphological basis, and interindividual variation of structural wing colouration in the common eggfly, Hypolimnas bolina L. (Nymphalidae). Males of this territorial species possess highly directional UV/violet colouration that fully overlaps smaller white patches on their dorsal wing surfaces. We sampled 56 males, including territorial residents and non-resident 'floaters' and assessed the properties of their structural colour using reflectance spectrometry and scanning electron microscopy. The patches reflect strongly in the UV range ( 300 - 400 nm), with a peak of similar to 360 nm, and the wing scales in these regions exhibit a ridge-lamellar surface architecture that has known function in other species as a multiple thin-film interference mirror. Peak UV brightness was variable, and both brightness and peak hue varied systematically across age classes. UV brightness was also related to hue independently of the age-related variation. Territorial residents possessed duller UV markings than their non-resident contemporaries, which is not consistent with exaggeration due to male - male competition. The high phenotypic variance is, however, consistent with a putative role for this male-limited trait as a sexual ornament.

Abstract: The study of sexual selection has recently been enriched by an explicit life history focus. This lifetime perspective has much to offer the field; however, most existing interdisciplinary exchanges have restricted themselves to the context of mate choice and associated phenomena. The present study explores the consequences of an explicit life history view upon the evolution of male-male contest competition. Key to this view is the fact that fighting typically has lifetime consequences, and thus the costs involved with contests are best considered in lifetime currencies such as residual reproductive value. The rate of contemporary contest cost accrual may vary among contestants due to differences between them in what they 'stand to lose', in terms of future reproductive opportunities. It is also suggested that it may be fruitful to partition key life history parameters into components that are either dependent or independent of future choice of mating strategy. Using a simple simulation, it is demonstrated that the optimum pattern of lifetime contest participation may vary depending upon lifetime variation in 'strategy-independent' components of reproductive value (such as the rate of mortality experienced in contexts unrelated to mating behaviour). In line with previous models of age-specific sexual advertisement, increasing lifetime aggression appears as the most favoured strategy; however, young age aggression is predicted if resource holding potential is expected to decline with age irrespective of prior contest participation. The model is discussed, along with key concepts surrounding the life history viewpoint, in light of prior life history/sexual selection models and the existing empirical data regarding lifetime fighting strategies in the wild. (c) 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 88, 565-578.

Abstract: The males of many butterflies are more brightly coloured than conspecific females and this sexual dichromatism often extends into ultraviolet (UV) wavelengths. Sexual selection, acting either in the context of intra- or intersexual interactions. is thought responsible for the relative brightness of the male visage: however, this hypothesis has been difficult to test experimentally. In this study, we undertake an indirect evaluation of this idea by analysing the phylogenetic distribution of two elements of male colour pattern - UV reflectance and melanic markings - in North American sulphur butterflies. Only the UV element, which derives from nanometre-scale surface structures and is extremely bright and spectrally pure, is expected to be of sexually selected origin. We therefore predicted, based upon prior theoretical treatments. that UV colour pattern should exhibit a polyphyletic distribution typical of a sexually selected trait, whereas melanic patterns should not. We charted the distribution of each colour element across the dorsal hind- and fore-wing surfaces of 26 species (spanning four genera), and summarized the resulting intraspecific variation in colour pattern using principal components analysis. Analysis of among- versus within-sister species group variance confirmed, as predicted, a largely polyphyletic distribution for UV but not melanic patterns. We also found that variation in fore-wing UV patterning could be considered orthogonal of hind-wing variation. These findings shed interesting light on the evolution of structural coloration in this group and add strength to the idea that brilliant male coloration is principally of sexually selected origin.

Abstract: Males of the wasp Palmodes praestans engage in non-territorial patrolling behaviour within a scramble competition mating system, showing great fidelity to their wide-ranging patrolling routes without attempting to monopolize the areas covered. Scramble competition appears adaptive given that mating opportunities are not spatially aggregated in this species, whose females build isolated, single-celled nests. Because of the female distribution pattern, a male's reproductive success in P. praestans probably depends upon the ability to find highly scattered, unmated females. The females of some close relatives of this sphecid wasp form fairly dense nesting aggregations. As mating system theory predicts, the males of some (but not all) of these species focus their searching at these concentrated nesting/emergence sites where potential mates are clustered spatially.

Abstract: Territorial behaviour is widespread among insects and serves as an important constituent of male reproductive success. In butterflies, competition for perching sites is mediated through aerial persistence duels in which the mechanisms of resolution have remained obscure. There is evidence in some species for an effect of age upon contest outcome, which could arise due to individuals adopting lifetime strategies of reproductive risk taking, or as a consequence of lifetime changes in resource-holding potential (RHP). RHP in territorial insects is often equated to the ability for sustained or high-performance flight, and if the morphological and/or energetic determinants of flight performance vary with age then this may explain putative age effects. I addressed this possibility by charting the correlates of residency in two nymphalid species, Hypolimnas bolina L. and Melanitis leda L., at popular perching sites in tropical Australia. Among samples of 55 male H. bolina (20 residents paired to 35 non-residents) and 36 male M. leda (13 residents paired to 23 non-residents), I found moderately sized relationships (effect sizes, d = 0.46-0.79) between residency and the studied biophysical variables (body size, absolute and relative lipid stores, and relative flight musculature). However, differences in age were always much larger (effect sizes, d = 1.23-1.52), with old male H. bolina and young male M. leda favoured for residency. The most parsimonious logistic model of residency in each case proved to be the model containing age only; hence, this study supports the notion of primarily age-based competitive strategies in these two butterflies.

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Abstract: Adaptations that enhance fitness in one sex may be harmful to members of the opposite sex and lead to antagonistic coevolution between the sexes. In fruit flies, for example, selection for fertilization success has rendered the male ejaculate slightly toxic to females. Here we investigated whether mating imposes a cost upon female fitness in a polyandrous pierid butterfly (Colias eurytheme) by comparing life history traits between once-mated females and virgins. Mated females laid relatively more eggs early in their adult life, but suffered a reduction in longevity relative to virgins held under identical experimental conditions. The effect of mating on female survivorship was statistically independent of lifetime and early life fecundity. Moreover, lifetime fecundity co-varied positively with longevity across all females, and across females within each treatment group, hence there was no phenotypic trade-off between survival and reproduction. These results suggest that the observed longevity difference between virgin and mated females represents a true cost of mating, possibly arising from a toxic side effect of the male ejaculate. However, irrespective of this cost, virgin and mated females laid an equivalent lifetime number of eggs. Female C. eurytheme are also known to use nutrients from the male ejaculate to supplement their reproductive output, hence it is presently unclear how the observed longevity cost may have influenced the evolution of lifetime mating schedules in this polyandrous species.

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Abstract: The bot fly Cuterebra austeni exhibits year-to-year consistency in its landmark-based hilltopping mating system. Flies were found on some of the same localized ridgetop perching areas that were known to be mate encounter sites 22 years previously. In both 1980 and 2002, males were drawn preferentially to locally elevated, largely vegetation-free sites. In addition, a substantial proportion of individuals exhibited site fidelity in both years, as demonstrated by their willingness to return to the site where marked after being captured and handled. In both years of observation, a smaller proportion returned the second day after marking and only 10-20% of marked males were seen on the third day. Thus males apparently have only a very limited window of opportunity to secure a given perching territory. In both years, a number of males ("residents") succeeded in monopolizing a perching area over a substantial part of the brief morning flight period. One unexplained difference across the decades: residents appeared on a lower proportion of days of observation in 2002 than in 1980.

Abstract: The evolutionary significance of body size variation in male insects is often obscure. One way in which this parameter could affect reproductive success is via its relevance to thermoregulation. In this study we investigated the relevance of body size to heat exchange rates in a tropical nymphalid, the common eggfly (Hypolimnas bolina) (L.). Males of this territorial species elevate their body temperature above ambient levels via a series of basking postures coupled with strategic choice of perching microhabitat. In an experiment with dead butterfly models we found, as expected, heightened rates of heat exchange (heating and cooling rates) in smaller individuals. There was also a significant interaction between basking posture and body size, with smaller individuals exhibiting significantly greater variation in heating rate with increasingly open wing postures. This suggests that smaller males would have greater control over their rate of basking heat gain ( by having at their disposal a greater potential range of heating rates), but they would also radiate body heat at a higher rate than their larger conspecifics. Using 'grab and stab' techniques, we found no evidence that smaller individuals are closer to their putative thermal optimum under a range of ambient conditions in the field. However, a more substantive field program, incorporating a more precise characterisation of the ambient thermal environment, will be required to fully evaluate the thermal significance of body size variation in males of this territorial butterfly.

Abstract: The question of why territorial residents usually win asymmetrical owner-intruder contests is critical to our understanding of animal contest evolution. Game theory suggests that, under certain conditions, residency could be used as an arbitrary means of contest settlement in a manner analogous to tossing a coin. Key empirical support for this idea is provided by a study on the speckled wood butterfly (Pararge aegeria); however, this result has proven controversial. We show conclusively that residency does not serve as an arbitrary cue for contest settlement in this species. By means of a series of manipulative experiments, conducted on two phenotypically divergent populations of P. aegeria, we also rule out the recently presented alternative that contests are settled due to resource-correlated asymmetries in thoracic temperature. Our results instead suggest that more intrinsically aggressive males accumulate as residents and continue to win due to the self-reinforcing effect of prior winning experience. Truly arbitrary contest settlement may be rare or non-existent in the wild.

Abstract: Butterflies are conspicuous among animals that fight for mating opportunities because it is not clear how contest costs could accrue. Nevertheless, the bulk of research in this group suggests that contests are settled on the basis of asymmetries in fighting ability (the superior competitor hypothesis). There is also a consistent effect on contest escalation due to apparent 'confusion' over residency, which could result from resident butterflies playing different tactics than non-residents, or from a causal link between residency and fighting ability. I addressed these hypotheses by studying contest behavior in the crepuscular species Melanitis leda (L.) (Nymphalidae) over a 5-month period in tropical Australia. Males competed via conspicuous two-stage maneuvers of a form unique among butter-flies. Prior residents won 77% of all contests. Non-resident males arrived and perched in occupied sites until challenged by incumbent residents, and the aggressiveness of these interlopers increased as a function of the time before they were detected. Contest winners also tended to be younger than losers, and contest escalation was negatively related to both the age of the losing, male and the magnitude of the between-combatant age asymmetry. These results are consistent with the superior competitor hypothesis based upon age as a determinant (or correlate) of fighting ability, but also suggest residency has a unique influence on contest behavior. Further research is clearly required to unravel the effects of age, residency and other potential biophysical determinants of fighting ability in this species.

Abstract: Adaptationist analyses of animal contests have contributed much to our understanding of behavioral evolution. One class of contest, however, the war of attrition, has proven difficult to interpret. In wars of attrition involving aerial displays, there is evidence that asymmetries in performance parameters such as flight energetics may be important determinants of contest resolution. This paradigm is not universal, however, and we presently lack a framework for understanding why certain biophysical parameters are important only in some cases. One possibility is that the relevance of these parameters is determined by evolutionarily conserved life-history-scale patterns of resource allocation and acquisition. We evaluated this hypothesis by investigating the correlates of competitive success in two territorial insects that exemplify markedly different lifetime patterns of resource utilization. We found that in the bot fly Cuterebra austeni, an extreme capital breeding species that depends entirely on energy acquired during its immature stages, territorial residency was most strongly correlated with a size-independent measure of energetic availability. In contrast, residency in the tarantula hawk wasp Hemipepsis ustulata was best predicted by variation in body size per se. Adult H. ustulata are able to supplement their larval-derived nutrient capital in the manner of an income breeder, and fuel reserves were independent of age and actually correlated negatively with residency in this species. These results underscore how the study of sexually selected phenomena may be enriched by an explicit consideration of life-history principles.

Abstract: Most colour in nature arises from pigments, but the most brilliant, deeply saturated visual signals have structural origins. These colours are generated from nanoscale structural arrays that interact with incident light to produce specific optical effects. Perhaps the most dazzling of nature's signals, the iridescent colours of tropical butterflies, have long been known to originate from such structures. However, new research by Vukusic and colleagues reveals the true depths to which evolution has crafted these fascinating optical devices.

Abstract: The males of many butterfly species compete for territories via conspicuous aerial wars of attrition, in which the determinants of persistence ability are largely unclear. Flight performance features, such as stamina, acceleration, and maneuverability, are often assumed to be important in this context, yet there is no direct evidence by which to evaluate these possibilities. Recent research has indicated that competitive ability increases with age in notably territorial species, Hypolimnas bolina, which could arise from lifetime morphological or physiological changes that directly affect flight muscle ratio (FMR), and wing condition change with age in this species. Males in five age categories (spanning the functional life span of territorial individuals) were sampled from encounter sites in tropical Australia. Analysis of body composition with respect to an estimate of eclosion mass (forewing length) indicated that total body mass, abdomen mass, and wing area decrease throughout an individual's lifetime, but thorax mass remains unchanged. Wing loading (the ratio of wing area to body mass) is lowest in intermediately aged individuals, but FMR and energetic status remain largely similar regardless of age. On average, therefore, the energetic cost of sustained flight should first decrease, then increase, with age in a male H. bolina (of standardized body size), while available energy reserves decline slightly. Acceleration and maneuverability should remain relatively constant. These results, coupled with the fact that body size is unrelated to contest success in this territorial butterfly, fail to support the idea that age-related competitive ability is mediated simply by energetics or flight performance.

Abstract: The requirement for efficient thermoregulation has directed the coevolution of specialized morphological and behavioural traits in ectotherms. Adult butterflies exhibit three thermoregulatory mechanisms, termed dorsal, lateral and reflectance basking. In this study, we investigate a potential fourth mechanism whereby individuals perch with their wings fully spread and angled downwards such that the margins are appressed to the substrate. We find that mate-locating male Hypolimnas bolina (L.) (Nymphalidae) adopt this posture when operational thoracic temperatures are lowest (less than approximately 34 C). As thoracic temperature increases, males perch with wings increasingly closed and ultimately select shaded microhabitats. Using thermocouple-implanted dead models, we show that appressed posture individuals warm faster than those adopting the conventional dorsal-basking (horizontal wing) posture. This thermal advantage is not mitigated by shading of the outer 60-70% of the wing area, which suggests that - as with the conventional dorsal posture only the basal wing surfaces contribute to heat gain via the absorption of solar irradiation. These investigations suggest that appression represents a novel extension of conventional dorsal basking behaviour in butterflies.

Abstract: Trait evolution via sexual selection has traditionally been viewed as isolated from life-history constraints. Recent theoretical treatments, however, predict that costly sexually selected characters should be mediated by the same allocational trade-offs that apply to more conventional aspects of reproductive investment. Participation in risky competitive behaviours, for example male-male combat, should therefore increase as the opportunity for future reproduction declines. However, the demonstration of such trade-offs has proven to be elusive due to concomitant age-based variation in the physical determinants of fighting 'ability'. Here, I exploit the unique nature of a butterfly contest system to provide compelling evidence for lifetime partitioning of risky and aggressive sexually selected behaviours. I show that male Hypolimnas bolina become more willing to persist in contests over mating territories, and more generally accepting of injury risks, as they age. Contest persistence in this species is not mediated simply by physical condition, and I experimentally isolate the effect of ageing per se from resource ownership and previous contest experience. These results demonstrate how sexually selected behaviours can be ultimately mediated by a shifting trade-off between contemporary reproductive effort and future opportunities.

Abstract: As in most animals, male butterflies are generally the more proactive sex with respect to seeking out mating opportunities. In most cases, males conduct their search sometime between mid-morning and mid-afternoon, but a few species are active only before dawn or after sunset. These crepuscular species offer a good opportunity to study how males deal with markedly different visual and thermal conditions. Here, I present data from a 5-month behavioural study of male Melanitis leda (Nymphalidae) at a mate-encounter site in tropical Australia. Males of this species defended perching locations along a forest edge in a similar manner to other diurnally active territorial nymphalids. They generally arrived at these sites after sunset and arrived earlier on evenings that darkened earlier. Actively mate-locating males were only seen at the site during a 25-35 min evening period, during which ambient light levels ranged between 50 and 2600 lux. Only 27% of marked territory residents were recorded again at their location of capture, but fidelity in this 'resighted' group ranged up to 23 days. A sample of males, captured under ambient temperatures of 24.0-27.2degreesC, maintained a mean thoracic excess of 8.25 +/- 0.73degreesC, but did not appear to 'shiver' in the manner of other crepuscular species. Males courted conspecific females and one mating was observed. This species is an excellent candidate for further research into the evolution of mating tactics in crepuscular butterflies.

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Abstract: The study of butterfly behavior has afforded valuable insights in to the evolution of alternative mating tactics Two hypotheses derived from this area of research contend that (1) territoriality is only viable under low to moderate conspecific densities (due to the costs of site defence) and (2) perching may be employed only when thermal conditions constrain flight activity. These hypotheses were evaluated by investigating mate locating behavior in Hypolimnas bolina, a territorial species that is naturally subject to variation in population density and weather conditions. Male behavior was charted throughout the day during a period of high population density at art encounter site in tropical Australia. Perching was the primary tactic, although a small proportion of individuals patrolled nonaggressively in the afternoon. Population-level male behavior failed to support predictions drawn from either the "territory economics" or "thermal constraint" hypotheses. First, the proportion of perching males and the number of aggressive conspecific interactions (per male) increased with increasing male density at the site. Second few males patrolled at the honest, brightest rime of day (approximately midday), and the diel distribution of perchers did not emulate the "U-shaped" distribution shown by the occurrence of dorsal basking behavior. These results show that perching in this species is not a suboptimal tactic employed when temperatures constrain flight activity but may represent the best method of locating receptive females. Ar this stage the reproductive significance of the observed patrolling behavior remains obscure.

Abstract: Phenotypic plasticity may enable organisms to maximize their fitness in seasonally variable environments. However, in butterflies, seasonal polyphenism is often striking but functionally obscure. This paper addresses the possible adaptive significance of phenotypic variation in the tropical butterfly Hypolimnas bolina (L.) (Nymphalidae). Plasticity in body size and wing coloration can be elicited in this species under laboratory conditions, however it is not known how this plasticity is expressed in the wild. Moreover, adult H. bolina spend the winter dry season in a reproductive diapause, which allows certain predictions regarding the occurrence of seasonal plasticity. Based on consideration of the requirements of diapausing and directly developing individuals, we predicted that if seasonal plasticity in phenotype were adaptive, then overwintering individuals should be larger and darker than their directly developing counterparts. This prediction was largely - although not entirely - fulfilled. Dry season butterflies were duller and darker than their wet season counterparts (this plasticity was superimposed on a genetic colour polymorphism), however size plasticity varied geographically. Dry season adults were consistently larger than wet season adults in the tropical north, but not in the south. We use these findings to discuss the possible adaptive significance of seasonal variation in the colour and size of this tropical butterfly. (C) 2001 The Linnean Society of London.

Abstract: The males of many territorial animals exhibit significant interindividual variation in site fidelity. A general Prediction from theoretical models is that site fidelity should increase as a function of male age. In this study, I investigated the relationship between age and site fidelity in the territorial nymphalid butterfly Hypolimnas bolina (L.). A total of 144 males from a population in tropical Australia were captured and marked over two seasonal rounds in 1998. Sampling of the subsequent fidelity of these marked individuals provided two related lines of evidence in support of the age-based prediction. First, older males were more likely to be resighted at their territories on at least one occasion following their capture and marking. Second, the subsequent site fidelity of the group of males that was resighted at least once was related to age, with older males showing greater average fidelity. Both results were consistent across seasons. Taken in concert, these findings strongly support the hypothesis that fidelity is linked to age in this territorial butterfly. At this stage it is not possible to distinguish between increased competitive ability and increased motivation for fidelity as the underlying cause of this relationship.

Abstract: The males of many butterfly species compete via pair-wise intrasexual contests, yet lack any obvious morphological traits conventionally associated with animal aggression. The evolution of contest behavior in this group is therefore interesting because the means by which individuals are able to inflict costs upon each other during combat are unclear. Here we review the relevant empirical information within a game-theoretical context in order to analyze contest-related costs and mechanisms of dispute settlement. Territorial butterfly contests carry obvious role asymmetries, and individuals in the 'resident' role are more likely to win across all studied species. We use this phenomenon as a framework for gaining further insight into the evolution of contest settlement in this group. Four principal hypotheses are evaluated: (1) that residency is used as an arbitrary convention, (2) that residents stand to gain a greater payoff if successful, (3) that residency bestows higher resource-holding potential (RHP) on males in that role, and (4) that residents are males of intrinsically higher RHP. We found most support for the latter explanation (the 'superior-competitor' hypothesis), partly because the alternatives require a restrictive set of ecological conditions, but also due to positive support for the idea of intrinsic RHP. The strongest evidence is provided by species in which repeated interactions (between the same individuals) always have the same outcome, regardless of changes in residency status. However, we also found a consistent effect on contest duration due to apparent 'confusion over residency,' which suggests a conventional element to contest behavior. Although butterfly contests must be costly in some way, the literature provides limited insight into how costs accrue, and hence the determinants of contest RHP remain obscure. We suggest that careful experimentation, using 'natural' manipulations where possible, should prove most beneficial in identifying costs and exploring schedules of contest settlement in this group. Moreover, future investigations should be sensitive to the fact that butterfly territoriality and associated male-male interactions are seated within a broader ecological and life-historical context.

Abstract: Females of many species choose to mate with old rather than young males, possibly because older males pass superior genes on to their offspring. Recent theoretical and empirical investigations have rejuvenated interest in the evolution of mating preferences based on age, and in the relationship between longevity and fitness. If the cost of signalling is a reduction in future survival and reproduction, mate choice based on age is one possible outcome when males signal their genetic quality. These recent investigations highlight the importance of understanding sexual selection from a life-history perspective.

Abstract: Many male insects aggressively defend specific perching sites containing larval resources. There are three main explanations for how this behaviour could contribute to increased matings: perching males may aim to encounter (1) eclosing or freshly eclosed virgin females, (2) previously mated, ovipositing females, or (3) receptive females that visit these sites either specifically to mate or for other reasons. I evaluated these hypotheses by investigating the timing of post-eclosion female receptivity and the extent of polyandry within an Australian population of the butterfly Hypolimnas bolina (L.) (Lepidoptera: Nymphalidae). This species represents the group of butterflies in which males defend specific, geographically prominent, sites that overlap with the distribution of larval resources. Freshly emerged female H. bolina refrained from mating until their ovaries were close to maturation, resulting in a pre-mating period of 4-8 days. The presence of this substantial refractory period rules out the hypothesis that males defend pupation sites with the aim of mating with eclosing or freshly eclosed females. Secondly, almost 90% of females within the studied population carried only one spermatophore, a finding that mediates against the possibility that most perching males target (already mated) ovipositing females. The 'rendezvous-site' hypothesis is the most likely general explanation for territoriality in H. bolina; however, it remains unclear whether the distribution of larval hostplants per se has a primary influence on territory selection by males in this species.

Abstract: Male Hypolimnas bolina (L.) (Lepidoptera: Nymphalidae) defend perch sites as a method of visually locating receptive females. In this study we charted the spatio-temporal activity of perching males in tropical Australia to investigate (a) the extent to which male activity is thermally constrained, and (b) the physical attributes of selected perching sites. Butterflies were surveyed along two 5-15 m wide open corridors through dense vegetation, and this allowed the prediction that males should favour narrower corridor sections in order to maximize their visual search capability. This prediction was supported. Beyond corridor width, the distribution of favoured perches was not explained any further by patterns of shading, larval food plant distribution, or the presence of nectar resources. Males were active from 0800 to 1700 h. but the number of perching individuals varied throughout the day, and this pattern varied between the two transects. Most individuals perched along one transect in the morning (0900-1100 h), whereas activity along the other peaked around midday (1100-1300 h). This between-transect difference in male activity followed changes in shading between the transects, however this variable did not predict male distribution at the territory scale. Although ambient and black body temperatures were significantly related to population-level activity. these variables only predicted 15-55%, of the variance in male counts in individual transects. This result, viewed in conjunction with the limited available information on female receptivity, suggests that the timing of mate location in H. bolina may be primarily influenced by the daily pattern of female availability.

Abstract: Because seasonality in tropical environments is driven by variation in rainfall, phytophagous tropical organisms are expected to exhibit mechanisms of escape in space and time that allow them to synchronize their breeding efforts with suitably wet periods of the year. This hypothesis was addressed by studying the breeding phenology of the nymphalid butterfly Hypolimnas bolina (L.) in the Australian wet-dry tropics. This species favours small, herbaceous larval foodplants that either die off annually or exhibit marked declines in leaf quality during the dry season. As expected, reproductive activity in H bolina was broadly correlated with both rainfall and humidity, with individuals spending part of the dry season (early April to late August) sheltering in overwintering sites in a state of reproductive diapause. The timing of the overwintering period was similar between the 2 years, which suggests that individuals respond to seasonally predictable cues such as photoperiod. At least in 1998, the exit of butterflies from overwintering sites was relatively sudden and coincided with the first spring rainfall event. These findings suggest that H. bolina copes with seasonal adversity in the tropics by means of a regularly timed diapause.

Abstract: The common eggfly, Hypolimnas bolina (L.) (Lepidoptera : Nymphalidae), is an adult-diapausing tropical and sub-tropical species that exhibits seasonal plasticity in adult body size. Here I investigated (a) whether size plasticity in this species is due solely to variations in rearing temperature, or whether photoperiod is also involved, and (b) whether rearing photoperiod affects the timing of ovarian development in adults. Individuals were cultured at temperatures ranging from 21 degrees C to 30 degrees C, and under daylengths of 11.5, 12.5 and 13.5 h in two separate experiments. Significant plasticity in juvenile developmental traits was detected in response to both variables, with cooler temperatures and shorter daylengths both leading to decreased developmental rates and increased size at maturity. Although juveniles grew more slowly with decreasing temperature, they grew faster with decreasing daylength. The timing of ovarian maturation was also related to rearing photoperiod; whereas 'long day' adults (13.5-h photoperiod) had gravid ovaries after 10 days, the ovaries of 'short day' adults (11.5-h photoperiod) were either regressed or nearly so. These preliminary results suggest that size variation observed in field populations of H. bolina may not be wholly accounted for by variations in developmental temperature and, furthermore, that photoperiod may be used by this tropical species as an environmental cue for the seasonal timing of reproduction.

Abstract: Although intrasexual contests generally favor bigger or stronger individuals, the relevance of body size to war of attrition-type disputes between weaponless animals such as butterflies is unclear. In this study I aimed to investigate the significance of size in this context by studying territorial contests in Hypolimnas bolina (L.), a species that exhibits consistent seasonal plasticity in body size. In this species adult age is positively correlated with large size in spring but with small size in autumn. This shift allowed independent evaluation of the relevance of each variable (size and age) to intrasexual contest success. Observation of a population of marked individuals indicated that only age appeared important, with the winners of pair-wise contests significantly older than losers in both seasons, and with contests lasting longer when the age difference between the combatants was small. Age was also linked to residency; residents won 99% of all contests. This study suggests that size does not matter in these aerial disputes, but age and residency do. It is not yet possible to determine whether older butterflies are intrinsically better competitors, or whether they simply have greater opportunity to find a vacant territory.

Abstract: Observations were made on the oviposition behaviour of post-diapause adults of Hypolimnas bolina (L.) at a site in Townsville, Australia (19 degrees 15'S, 146 degrees 45'E). Females most often laid one or two eggs on freshly emerged seedlings (<10 mm height) of Synedrella nodiflora a (L.) (Asteraceae). Mature foodplants of S. nodiflora, Sida rhombifolia (L.), Sida acuta (Burm. f) and Malvastrum coromandelianum (L.) (all Malvaceae) were present, and occasionally sampled by females, but were ignored as oviposition substrates. Females were present at the site from 0900 to 1500 hours, and were more persistent than their male counterparts under adverse environmental conditions (i.e, reduced temperature and solar radiation). The relatively high number and apparent selectiveness of ovipositing females in this situation indicates the importance placed on utilising fresh growth of the larval foodplant. This behaviour may serve to maximise the rate of return per unit reproductive effort of post-diapause females.