Seasonal plasticity in sympatric Bicyclus butterflies in a tropical forest where temperature does not predict rainfall

Abstract

While variation in temperature appears to be the main environmental cue for plasticity in adult traits in many species of Mycalesina, relying on temperature would result in a mismatch between adult phenotype and environment in some regions. We measured phenotypes of six species of Bicyclus butterflies (Nymphalidae: Satyrinae: Mycalesina) in a humid tropical forest with two rainy seasons per year and modest unimodal seasonal temperature variation, such that temperature does not predict rainfall and butterflies can reproduce year-round. The butterflies showed subtle temporal variation in body size and relative eyespot size, while relative androconia length was robust to temporal environmental variation. After higher temperatures, body size tended be smaller, and relative eyespot size was larger for some species-eyespot combinations. This indicates that these butterflies follow the “hotter is smaller” rule, and show developmental plasticity in eyespot size that is typical in this clade. Eyespot sizes tended to be correlated with each other, except Cu1 in B. auricruda and some eyespots that always remained very small. Androconia length was not related to eyespot size. This pattern of correlations suggests conserved cue-use and shared mechanisms for eyespot size using both temperature and rainfall-related cues, with some exceptions.