Genetic and phenotypic variation in a colourful treefrog across five geographic barriers

Aim  Understanding the patterns and processes underlying phenotype in a polytypic species provides key insights into microevolutionary mechanisms of diversification. The red-eyed treefrog, Agalychnis callidryas, exhibits strong regional differentiation in colour pattern, corresponding to five admixed mitochondrial DNA clades. We evaluated spatial diversity patterns across multiple, putative barriers to examine the fine-scale processes that mediate phenotypic divergence between some regions while maintaining homogeneity between others. Location  We examined patterns of phenotypic diversification among 17 sites that span five putative biogeographic barriers in lower Central America (Costa Rica and Panama). Methods  We tested the extent to which genetic distance (FST) derived from six multilocus nuclear genotypes covaried with measures of phenotypic distance (leg coloration) within and between biogeographic regions. We used linear regression analyses to determine the role of geographic and genetic factors in structuring spatial patterns of phenotypic diversity. Results  The factors that best explained patterns of phenotypic diversity varied among biogeographic regions. We identified one geographic barrier that impeded gene exchange and resulted in concordant phenotypic divergence across the Continental Divide, isolating Caribbean and Pacific populations. Across Caribbean Costa Rican populations, one barrier structured phenotypic but not genetic diversity patterns, indicating a role for selection. In other regions, the putative barriers had no determining effect on either genetic or leg colour structure. Main conclusions  The processes mediating the distribution and diversification of colour pattern in this polytypic, wide-ranging treefrog varied among biogeographic regions. Spatially varying selection combined with the isolating effects of geographic factors probably resulted in the patchy distribution of colour diversity across Costa Rican and Panamanian populations.