Potential direct fitness consequences of ornament-based mate choice in a butterfly

Ultraviolet signaling in a butterfly is preferred by females and conveys male genetic quality

Indicator models of sexual selection posit that females choose males on the basis of traits that reveal male genetic quality and thereby enjoy increased offspring production. Here, we report that females of the butterfly Eurema hecabe receive indirect benefits from choosing males based on their ultraviolet (UV) wing coloration, a heritable and condition-dependent trait in this species. We first used a large laboratory-bred pedigree to demonstrate a per-family association between inbreeding and male UV trait value. Females exerted choice for UV-bright males within this protocol, and the average male UV trait value increased over six consecutive generations, presumably due to such selection and despite an increasing rate of pedigree-wide inbreeding. We then experimentally imposed a standard strength of inbreeding upon lines of divergent male UV trait values. Inbreeding depressed the siring performance of low UV treatment males more severely and resulted in a marginal reduction of their UV brightness, which rebounded sharply following subsequent outcrossing. These findings are consistent with the ornament-based signaling of genetic quality as a function of underlying individual-level mutational load.

Natural and sexual selection shape the evolution of colour and conspicuousness in North American wood-warblers (Parulidae)

Natural and sexual selection drive colour evolution in animals. However, these different selective forces are often studied independently or without considering environmental variation. We evaluated the roles of natural and sexual selection together on colour evolution in 15 sympatric wood-warbler species, while considering the influence of variation in the light environment and visual background. We tested the influence of each selective pressure on male and female coloration and contrast against the background using avian visual models in phylogenetically controlled analyses. We found natural and sexual selection simultaneously driving cryptic and conspicuous plumage in males by acting on different body regions. For example, we found that ground-nesting species had males with conspicuous under-body plumage and cryptic upper-body plumage, showing how natural and sexual selection can drive colour evolution concordantly. We also found interesting relationships with female plumage, such as nest predation positively covarying with female contrast against the background, suggesting a cost to female conspicuousness. Our findings here showcase the complexity of selection on coloration and illustrate the importance of: (1) accounting for environmental variation when assessing how natural and sexual selection drive colour evolution; and (2) testing how multiple selection pressures are shaping colour diversity among species.

Quantitative characterization of iridescent colours in biological studies: a novel method using optical theory

Iridescent colours are colours that change with viewing or illumination geometry. While they are widespread in many living organisms, most evolutionary studies on iridescence do not take into account their full complexity. Few studies try to precisely characterize what makes iridescent colours special: their angular dependency. Yet, it is likely that this angular dependency has biological functions and is therefore submitted to evolutionary pressures. For this reason, evolutionary biologists need a repeatable method to measure iridescent colours as well as variables to precisely quantify the angular dependency. In this study, we use a theoretical approach to propose five variables that allow one to fully describe iridescent colours at every angle combination. Based on the results, we propose a new measurement protocol and statistical method to reliably characterize iridescence while minimizing the required number of time-consuming measurements. We use hummingbird iridescent feathers and butterfly iridescent wings as test cases to demonstrate the strengths of this new method. We show that our method is precise enough to be potentially used at intraspecific level while being also time-efficient enough to encompass large taxonomic scales.

Mating status correlates with dorsal brightness in some but not all poison frog populations

Sexual signals are important for intraspecific communication and mate selection, but their evolution may be driven by both natural and sexual selection, and stochastic processes. Strawberry poison frogs (Oophaga pumilio) show strong color divergence among populations, but coloration also varies among individuals of the same population. The importance of coloration for female mate choice has been studied intensely, and sexual selection seems to affect color divergence in strawberry poison frogs. However, the effect of coloration on mating success under field conditions has received very little attention. Furthermore, few studies examined how phenotypic variation among individuals of the same color morph affects mate selection under natural conditions. We measured the spectral reflectance of courting and noncourting individuals and their background substrates in three geographically separated populations. In one population (Sarapiquí, Costa Rica), we found that naturally occurring courting pairs of males and females had significantly brighter dorsal coloration than individual males and females not engaged in courtship interactions. Our field observations suggest that, in the wild, females prefer brighter males while the reason for the higher courtship activity of brighter females remains unclear. Overall our results imply that brightness differences among individuals of the same color morph may actually affect reproductive success in some populations of strawberry poison frogs.

Males Become Choosier in Response to Manipulations of Female Wing Ornaments in Dry Season Bicyclus anynana Butterflies

Male investment towards reproduction is substantial in some species, and this leads to the evolution of choosy males. Male choice is often directed towards female phenotypes that are good indicators of fecundity such as body size, age, or virgin status, and often acts in the same direction as fecundity selection. In insects, only a few examples exist where male choice is directed towards female ornaments as proxies Butler of female quality. Here, we use dry season males of the sex-role reversed butterfly species Bicyclus anynana to test for differences in male choosiness and investment towards females of varying attractiveness using ornament-manipulations. Male reproductive investment in this species is in the form of a nuptial gift, a spermatophore, given to females upon mating. Males were placed in cages with either wild-type ornamented females or with nonornamented females (center of the dorsal forewing eyespots painted over), and time to mating, duration of mating, and longevity of males and females after a single mating were measured. Ornament manipulations consisted of blocking the UV-reflective scales in the center of the dorsal forewing eyespots of females, a known sexual ornament. Males displayed lower latency to mate and longer mating durations with ornamented females. The longer mating duration did not, however, translate in the transfer of a nuptial gift that increased female longevity or reduced male longevity. Instead, we propose that longer mating durations with ornamented females may represent increased mate guarding behavior or increased sperm transfer.

The male sex pheromone of the butterfly Bicyclus anynana: towards an evolutionary analysis

Background

Female sex pheromones attracting mating partners over long distances are a major determinant of reproductive isolation and speciation in Lepidoptera. Males can also produce sex pheromones but their study, particularly in butterflies, has received little attention. A detailed comparison of sex pheromones in male butterflies with those of female moths would reveal patterns of conservation versus novelty in the associated behaviours, biosynthetic pathways, compounds, scent-releasing structures and receiving systems. Here we assess whether the African butterfly Bicyclus anynana, for which genetic, genomic, phylogenetic, ecological and ethological tools are available, represents a relevant model to contribute to such comparative studies.

Methodology/Principal Findings

Using a multidisciplinary approach, we determined the chemical composition of the male sex pheromone (MSP) in the African butterfly B. anynana, and demonstrated its behavioural activity. First, we identified three compounds forming the presumptive MSP, namely (Z)-9-tetradecenol (Z9-14:OH), hexadecanal (16:Ald ) and 6,10,14-trimethylpentadecan-2-ol (6,10,14-trime-15-2-ol), and produced by the male secondary sexual structures, the androconia. Second, we described the male courtship sequence and found that males with artificially reduced amounts of MSP have a reduced mating success in semi-field conditions. Finally, we could restore the mating success of these males by perfuming them with the synthetic MSP.

Conclusions/Significance

This study provides one of the first integrative analyses of a MSP in butterflies. The toolkit it has developed will enable the investigation of the type of information about male quality that is conveyed by the MSP in intraspecific communication. Interestingly, the chemical structure of B. anynana MSP is similar to some sex pheromones of female moths making a direct comparison of pheromone biosynthesis between male butterflies and female moths relevant to future research. Such a comparison will in turn contribute to understanding the evolution of sex pheromone production and reception in butterflies.