For its functional significance, diversity, and the relative ease of obtaining comparable measurements, coloration is one of the most tractable traits in evolutionary research. Color phenotypes are often under strong local selection pressures and can be strikingly different among related species or populations. In addition to regulatory differences, we found potential evidence of differential selection acting at the protein sequence level in several color-associated loci, which could contribute to the color polymorphism.Īnimal coloration plays important roles in intra- and interspecific communication, thermoregulation, predator avoidance and other ecological interactions with direct impact on individual fitness. However, the finding of differentially expressed genes across pathways and functional categories suggests that multiple mechanisms are responsible for the coloration differences, likely involving both pigmentary and structural coloration. The strong signal of differential expression in pteridine genes is consistent with a major role of these genes in generating the coloration differences among the three morphs. Gene expression in the skin of the three populations of frogs with differing coloration is highly divergent.
In addition to gene expression differences, we identified 370 outlier SNPs on 162 annotated genes showing signatures of diversifying selection, including eight pigmentation-associated genes. We detected significantly higher expression of the pteridine synthesis gene set in red and green frogs versus blue frogs. Notable upregulated examples include pteridine synthesis genes spr, xdh and pts (in red and green frogs) carotenoid metabolism genes bco2 (in blue frogs), scarb1 (in red frogs), and guanine metabolism gene psat1 (in blue frogs). We found 68 candidate coloration loci with significant expression differences among the color phenotypes. We then measured gene expression in individuals of the three color phenotypes and identified color-associated candidate genes by comparing differential expression results against a list of a priori gene sets for five different functional categories of coloration – pteridine synthesis, carotenoid synthesis, melanin synthesis, iridophore pathways (structural coloration), and chromatophore development. We generated a high quality non-redundant reference transcriptome by mapping the products of genome-guided and de novo transcriptome assemblies onto a re-scaffolded draft genome of O. pumilio from the Bocas del Toro archipelago in Panama.
Here we quantify gene expression and genetic variation to identify candidate genes involved in generating divergence in coloration between populations of red, green and blue O. The strawberry poison frog ( Oophaga pumilio) shows an impressive array of color morphs across its distribution in Central America. Animal coloration is usually an adaptive attribute, under strong local selection pressures and often diversified among species or populations.