The Role of the Melanocortin-1 Receptor Gene in Müllerian Mimic Ranitomeya imitator

Abstract

The Peruvian poison dart frog Ranitomeya imitator has undergone a Müllerian mimetic radiation, which means that this species has evolved color patterns that mimic three other poison dart frogs in different geographic regions of north-central Peru, banded for R. summersi (Sauce), orange-headed for R. fantastica (Varadero), and two morphs, striped (lowland) and spotted (montane), for R. variabilis. Even though these morphs have shown strong phenotypic differentiation there are varying levels of other processes between transition zones like reproductive isolation, geographic isolation, and natural selection, that affect the extent to which divergence has occurred. This speciation continuum makes for a useful model to study the relationship between selection and mimicry and how this combination may lead to incipient speciation. Color pattern has been suggested to play a role in this process, so our study focused on the melanocortin-1 receptor gene, which is known to affect color pattern in other species. We found a nonsynonymous single nucleotide polymorphism between the striped and banded morphs in this gene, which codes for eumelanin and black coloration. Genetic analyses revealed significant positive selection acting on multiple codons across sequences from different species of frogs, including the single nucleotide polymorphism we identified, which suggests that the melanocortin-1 receptor gene plays a role in driving divergence between these morphs. Future experiments will study the genetic association of color variation and sequence variation for other color candidate genes to identify main contributors to this unique example of divergence between four morphs from a Müllerian mimetic radiation.