Evolutionary tradeoffs between male secondary sexual traits revealed by a phylogeny of the hyperdiverse tribe Eumaeini (Lepidoptera: Lycaenidae)

Male butterflies in the hyperdiverse tribe Eumaeini possess an unusually
complex and diverse repertoire of secondary sexual characteristics
involved in pheromone production and dissemination. Maintaining multiple
sexually selected traits is likely to be metabolically costly, potentially
resulting in trade-offs in the evolution of male signals. However, a
phylogenetic framework to test hypotheses regarding the evolution and
maintenance of male sexual traits in Eumaeini has been lacking. Here, we
infer a comprehensive, time-calibrated phylogeny from 379 loci for 187
species representing 91% of the 87 described genera. Eumaeini is a
monophyletic group that originated in the late Oligocene and underwent
rapid radiation in the Neotropics. We examined specimens of 818 of the
1096 described species (75%) and found that secondary sexual traits are
present in males of 91% of the surveyed species. Scent pads and scent
patches on the wings and brush organs associated with the genitalia were
probably present in the common ancestor of Eumaeini and are widespread
throughout the tribe. Brush organs and scent pads are negatively
correlated across the phylogeny, exhibiting a trade-off in which lineages
with brush organs are unlikely to regain scent pads and vice versa. In
contrast, scent patches seem to facilitate the evolution of scent
pads, although they are readily lost once scent pads have evolved. Our
results illustrate the complex interplay between natural and sexual
selection in the origin and maintenance of multiple male secondary sexual
characteristics and highlight the potential role of sexual selection
spurring diversification in this lineage.