PCA coordinates describing dorsal colour pattern variation in 723 Morpho butterflies

Species interactions such as mimicry can promote trait convergence but
disentangling this effect from those of shared ecology, evolutionary
history and niche conservatism is often challenging. Here by focusing on
wing color pattern variation within and between three butterfly species
living in sympatry in a large proportion of their range, we tested the
effect of species interactions on trait diversification. These butterflies
display a conspicuous iridescent blue coloration on the dorsal side of
their wings and a cryptic brownish colour on the ventral side. Combined
with an erratic and fast flight, these color patterns increase the
difficulty of capture by predators and contribute to the high escape
abilities of these butterflies. We hypothesize that, beyond their direct
contribution to predator escape, these wing patterns can be used as
signals of escape abilities by predators, resulting in positive
frequency-dependent selection favouring convergence in wing pattern in
sympatry. To test this hypothesis, we quantified dorsal wing pattern
variations of 723 butterflies from the three species sampled throughout
their distribution, including sympatric and allopatric situations and
compared the phenotypic distances between species, sex and localities. We
detected a significant effect of localities on colour pattern, and higher
inter-specific resemblance in sympatry as compared to allopatry,
consistent with the hypothesis of local convergence of wing patterns. Our
results provide support to the existence of escape mimicry in the wild and
stress the importance of estimating trait variation within species to
understand trait variation between species, and to a larger extent, trait
diversification at the macro-evolutionary scale.