Under pressure: evidence for selection on color-related genes in poison frogs of the genus Ranitomeya

Aposematic organisms rely on their bright conspicuous coloration to communicate to potential predators that they are toxic and unpalatable. These aposematic phenotypes are strongly tied to survival and therefore make excellent opportunities to investigate the genetic underpinning of coloration. The genus Ranitomeya includes phenotypically diverse members of Neotropical aposematic poison frogs native to South America. Significant progress has been made in elucidating the molecular mechanisms responsible for aposematic coloration in poison frogs, which have paved the way for future studies to test hypotheses of the evolution of coloration across aposematic vertebrates. However, very little is known about whether these color related genes are under positive selection. We assembled transcriptomes from publicly available data reads sets for 9 different color morphs of poison frogs in the Ranitomeya genus that display bright conspicuous coloration (four morphs of R. imitator, two morphs of R. variabilis, two morphs of R. fantastica, one morph of R. summersi) to identify protein-coding genes responsible for color production that are under positive selection. Our results show that there are multiple genes under strong positive selection that are predicted to play roles in melanin synthesis (dct, tyrp1, irf4), iridophore development (fhl1), keratin metabolism (ovol1), pteridine synthesis (prps1, xdh), and carotenoid metabolism (adh1b, aldh2). The identification of positive selection affecting candidate color-pattern genes is consistent with the possibility that these genes mediate (in part) the molecular evolution of coloration. This may be attributed to aposematic phenotypes being directly tied to survival and reproduction in poison frogs.