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.

Maternal age affects offspring nutrient dynamics.

The internal physiological state of a mother can have major effects on her fitness and that of her offspring. We show that maternal effects in the parasitic wasp Eupelmus vuilleti become apparent when old mothers provision their eggs with less protein, sugar and lipid. Feeding from a host after hatching allows the offspring of old mothers to overcome initial shortages in sugars and lipids, but adult offspring of old mothers still emerged with lower protein and glycogen quantities. Reduced egg provisioning by old mothers had adverse consequences for the nutrient composition of adult female offspring, despite larval feeding from a high-quality host. Lower resource availability in adult offspring of old mothers can affect behavioural decisions, life histories and performance. Maternal effects on egg nutrient provisioning may thus affect nutrient availability and fitness of future generations in oviparous animals.