Selection and localised genetic structure in the threatened Manauense Harlequin Frog (Bufonidae: Atelopus manauensis)

Abstract

Knowledge of genome-wide variation and the processes influencing gene flow are critical to managing threatened species. Here, we characterise genetic diversity and the environmental features associated with connectivity for a narrowly distributed and threatened Amazonian frog, Atelopus manauensis. We sampled 94 individuals throughout the upper, middle and lower courses from each of the five major rivers covering the species’ known geographic range and genotyped each individual at 3859 single nucleotide polymorphisms (SNPs). Genetic variation was significantly subdivided into six groups, each mostly containing individuals sampled within the same major river system. The genetic distances among these groups increased with geographic distance, and open forests and the extremities of the altitude gradient were associated with less genetic connectivity. Using F_ST outlier approaches and environmental association analyses, we identified SNPs indicative of localised adaptation, with 28 SNPs significantly associated with forest biomass and altitude. Evidence of divergent selection among the six genetic clusters suggests the presence of six Evolutionary Significant Units (ESUs). Overall, the ESUs were characterized by low contemporary effective population sizes (N_E < 100) suggesting that genetic variation will be lost by random genetic drift. We demonstrate surprisingly high levels of divergence across the limited distribution of A. manauensis and suggest that each of the six adaptively divergent lineages be considered in conservation planning.