Genetic parallelism underpins convergent mimicry coloration in Lepidoptera across 120 million years of evolution

Abstract

Convergent evolution, the repeated evolution of similar phenotypes, is widespread in nature, but there are few studies investigating the genetic mechanisms of convergence across wide evolutionary timescales. The extent to which the same genetic mechanisms contribute to convergent evolution could reveal whether the pathway towards these fitness optima is flexible or constrained to follow a particular route, informing us about the predictability of evolution. Wing color pattern mimicry in Lepidoptera is a well-known example of convergent evolution, but as studies are restricted to a few closely related species, it is difficult to make general inferences about the predictability of evolution in this system. Here we study convergent evolution in multiple mimetic neotropical lepidopteran lineages that diverged between ~1 and 120 Mya, including seven species of Ithomiini and Heliconius butterflies and a day-flying Chetone moth. Across butterfly lineages that diverged up to ~30 Mya, the genetic variants most strongly associated with convergent color pattern switches are located in similar noncoding regions near the genes ivory and optix. In the more distantly related moth species, color pattern variation is associated with a ~1 Mb inversion which also contains ivory, closely mirroring the supergene architecture of the co-mimetic butterfly Heliconius numata. In contrast to previous studies on Heliconius butterflies, we find limited evidence that convergence among closely related Ithomiini species results from alleles shared by hybridization. Repeated parallel evolution of regulatory switches via reuse of the same two genes suggests that convergent color pattern evolution is highly constrained and predictable even across large evolutionary timescales. Such constraints may have facilitated diverse taxa joining this species-rich mimicry ring.