Divergent warning patterns influence male and female mating behaviours in a tropical butterfly

Abstract

Traits under divergent ecological selection that also function during mating can be important in maintaining species boundaries. Few studies have considered mutual mate choice, where both males and females base mating decisions on the same trait. We investigated the contribution of visual preference to assortative mating between an aposematic butterfly Heliconius cydno and its sympatric relative H. melpomene. Wing colouration in Heliconius butterflies evolved as a warning signal but also functions as a mating cue. We predicted that both sexes of H. cydno contributed to assortative mating by exhibiting visual preference towards conspecific wing colouration. We analysed published and new data from preference experiments, in which males were presented with conspecific and H. melpomene females. We also recorded female responses and mating outcomes in choice experiments, involving conspecific males with either the original white or artificially painted red forewing bands. Both sexes of H. cydno responded more positively towards the conspecific colouration, yet male colouration did not predict mating outcomes in female choice experiments. As courtships are initiated by males in butterflies, our findings suggest that female visual preference might be of secondary importance in preventing gene flow between H. cydno and H. melpomene.