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

Mating Delay Reduces Reproductive Performance but not Longevity in a Monandrous Moth

Age at mating is one of the most important factors that affect mating success and reproductive fitness in insects. The present study investigated how the age of the two sexes at mating determined mating success, reproductive fitness and longevity in Phauda flammans (Walker) (Lepidoptera: Phaudidae), a serious pest of Ficus spp. trees in South and Southeast Asia. The study may provide basic knowledge for the development of mating disruption programs using sex pheromones to control this pest. The species is monandrous and its adults live for only 4-5 d. We show that delayed mating significantly lowered mating success in both sexes, with males being more severely affected than females. Mating delay also reduced reproductive outputs of both sexes but females were more negatively affected than males. We did not find any effect of delayed mating on longevity of either sex. Our findings suggest that mating disruption with sex pheromones can be an effective method to delay mating in P. flammans, reducing reproductive success and thus limit population growth.

Polyphenism of visual and chemical secondary sexually-selected wing traits in the butterfly Bicyclus anynana: How different is the intermediate phenotype?

Polyphenism is a type of phenotypic plasticity supposedly adaptive to drastic and recurrent changes in the environment such as seasonal alternation in temperate and tropical regions. The butterfly Bicyclus anynana shows polyphenism with well-described wet and dry seasonal forms in sub-Saharan Africa, displaying striking morphological, physiological and behavioural differences in response to higher or lower developmental temperatures. During the seasonal transition in the wild, the intermediate phenotype co-occurs with wet and dry phenotypes. In this study, we aimed to characterize the secondary sexually-selected wing traits of the intermediate form to infer its potential fitness compared to wet and dry phenotypes. Among the previously described wing morphological traits, we first showed that the area of the fifth eyespot on the ventral hindwing is the most discriminant trait to identify wet, dry and intermediate phenotypes in both sexes. Second, we characterized the intermediate form for two secondary sexually-selected wing traits: the area and UV reflectance of the dorsal forewing pupil and the composition of the male sex pheromone. We showed that values of these two traits are often between those of the wet and dry phenotypes. Third, we observed increasing male sex pheromone production in ageing dry and wet phenotypes. Our results contrast with previous reports of values for sexually-selected traits in wet and dry seasonal forms, which might be explained by differences in rearing conditions or sample size effects among studies. Wet, dry and intermediate phenotypes display redundant sexually dimorphic traits, including sexually-selected traits that can inform about their developmental temperature in sexual interactions.

Male Bicyclus anynana Butterflies Choose Females on the Basis of Their Ventral UV-Reflective Eyespot Centers

Butterflies often use their dorsal and ventral wing color patterns for distinct signaling functions. Color patterns on hidden dorsal wing surfaces are often used in sexual signaling, while exposed ventral patterns are often used to ward off predator attacks. At rest, however, part of the ventral forewings are often hidden by the hindwings, allowing individuals to also use the patterns on this wing surface for sexual signaling. Here, we test this hypothesis in Bicyclus anynana (Butler, Lepidoptera, Nymphalidae) butterflies by first determining the degree of sexual dimorphism in ventral forewing patterns, focusing on the eyespots, from both wet and dry season forms, and then testing the role of the larger ventral forewing eyespots of dry season females in male mate choice. We also test male investment in reproduction. We show that ventral forewing UV-reflective eyespot centers, in addition to dorsal forewing eyespot centers previously examined in this species, play a role in sexual signaling as males preferentially mated with females with their ventral eyespot centers intact instead of blocked with black paint. This male preference, however, did not translate into a detectable higher reproductive investment via a single mating toward ornamented females. This study provides an example of how ventral forewing patterns, often hidden by hindwings, are used in sexual communication, in this case by females to attract males.

Sexual selection contributes to partial restoration of phenotypic robustness in a butterfly

Phenotypic variation is the raw material for selection that is ubiquitous for most traits in natural populations, yet the processes underlying phenotypic evolution or stasis often remain unclear. Here, we report phenotypic evolution in a mutant line of the butterfly Bicyclus anynana after outcrossing with the genetically polymorphic wild type population. The comet mutation modifies two phenotypic traits known to be under sexual selection in this butterfly: the dorsal forewing eyespots and the pheromone-producing structures. The original comet mutant line was inbred and remained phenotypically stable for at least seven years, but when outcrossed to the wild type population the outcrossed comet line surprisingly recovered the wild type phenotype within 8 generations at high (27 °C), but not at low (20 °C), developmental temperatures. Male mating success experiments then revealed that outcrossed comet males with the typical comet phenotype suffered from lower mating success, while mating success of outcrossed comet males resembling wild types was partially restored. We document a fortuitous case where the addition of genetic polymorphism around a spontaneous mutation could have allowed partial restoration of phenotypic robustness. We further argue that sexual selection through mate choice is likely the driving force leading to phenotypic robustness in our system.