The Influence of Environmental Variation on the Genetic Structure of a Poison Frog Distributed Across Continuous Amazonian Rainforest

Biogeographic barriers such as rivers have been shown to shape spatial
patterns of biodiversity in the Amazon basin, yet relatively little is
known about the distribution of genetic variation across continuous
rainforest. Here, we characterize the genetic structure of the
brilliant-thighed poison frog (Allobates femoralis) across an 880-km-long
transect along the Purus-Madeira interfluve south of the Amazon river,
based on 64 individuals genotyped at 7609 single-nucleotide polymorphism
loci. A population tree and clustering analyses revealed 4 distinct
genetic groups, one of which was strongly divergent. These genetic groups
were concomitant with femoral spot coloration differences, which was
intermediate within a zone of admixture between two of the groups. The
location of these genetic groups did not consistently correspond to
current ecological transitions between major forest types. A multimodel
approach to quantify the relative influence of isolation-by-geographic
distance (IBD) and isolation-by-environmental resistance (IBR)
nevertheless revealed that, in addition to a strong signal of IBD, spatial
genetic differentiation was explained by IBR primarily linked to dry
season intensity (r2 = 8.4%) and canopy cover (r2 = 6.4%). We show
significant phylogenetic divergence in the absence of obvious
biogeographical barriers and that finer-scaled measures of genetic
structure show patterns that are associated with environmental variables
also known to predict the density of A. femoralis.