Correlated evolution of multiple traits gives butterflies a false head

Many butterflies possess a combination of characters at the posterior hindwing end, superficially resembling their head. This <i>false head</i> has been hypothesized to deflect predator attacks towards the false head area. A clear understanding of the diversity and evolution of false head traits across butterflies is lacking. Here, we tested whether false head traits evolved from simple to complex in order to achieve a greater resemblance to a head. We also tested if false head traits form an adaptive constellation and, thus, evolved correlatedly. Using a phylogenetic framework with 928 lycaenid species, our results illustrate evolutionary patterns of five false traits: (i) false antennae; (ii) spot; (iii) conspicuous colouration in the false head area; (iv) false head contour in the false head area; and (v) convergent lines. We found that false traits (i)-(iv) evolved in a correlated fashion across the phylogeny, likely driven by a common selective pressure. Our findings support the idea that a false head functions as an adaptive constellation for predator attack deflection.