Tempo and mode of diapause evolution in butterflies

Quantifying the tempo and mode via modern phylogenetic comparative methods can provide crucial insights into the role of selection and constraints in trait evolution. Here we elucidate the evolution of diapause, a complex and defining life-history trait that allows temporal escape from unfavorable conditions in many insects, including our model system, butterflies. Using a thorough literature survey, we first scored the developmental stage of diapause (egg, larva, pupa, adult) vs. absence of diapause. We find that larval diapause is most common in temperate lineages while pupal, egg, and adult diapause are relatively rare. Next, we determined that the loss of diapause occurred at a much higher rate than the gain, and its gain primarily occurred from the non-diapause state. While ancestral state estimation at deeper nodes remained uncertain, we found consistent patterns for some families and strong evidence for the convergent evolution of diapause across butterflies. We found no support for the hypothesis that the rate of the gain of diapause should be higher during the Eocene-Oligocene glacial maximum event (~35 MYA). Overall, the evolution of diapause in butterflies has a complex history, has evolved convergently, and has likely evolved much earlier than the Eocene-Oligocene glaciation event consistent with the deep history of diapause evolution in insects. These findings fill a deep gap in much-needed studies for future comparative research.