Correlated evolution of multiple traits gives butterflies a false head

Abstract

Many butterflies possess a complex set of characters at the posterior hindwing end, superficially resembling their head. This 'false head' (FH) has been hypothesised to deflect predator attacks towards the FH area. The presence of the traits constituting a false head varies across butterflies, and a clear understanding of the diversity and evolution of FH traits across butterflies is lacking. Here, we tested whether FH traits evolved from simple to complex, more elaborate traits to achieve more head-like characteristics. We also tested if FH traits formed an adaptive constellation and, thus, evolved correlatedly. Using a phylogenetic framework with >900 lycaenid species, our results illustrate evolutionary patterns of five FH traits - (i) false antennae, (ii) spot, (iii) conspicuous colouration in the FH area, (iv) false head contour in the FH area, and (v) convergent lines. We found that FH traits (i)–(iv) evolved in correlated patterns across the phylogeny, likely driven by a common selective pressure. Our findings support the idea that FH functions as an adaptive constellation for predator attack deflection.