Global population structure in an arctic-breeding bird: Diversifying and
stabilizing selection consistent with local adaptation
Abstract
Environmental variation among isolated populations can drive genetic
differentiation by selection, while isolation alone results primarily in
genetic drift. Genetic analyses can aid in identifying genetically
isolated populations and population structure of a species across its
range. Additionally, such analyses can provide indirect evidence of
local adaptation through the comparison of allele frequencies at neutral
and functional genetic markers, with the aim of identifying outlier loci
consistent with the effects of selection. Here, we examine the genetic
divergence and patterns of functional divergence among six breeding
populations of arctic-breeding snow buntings (Plectrophenax nivalis). We
genotyped 221 birds at 9 microsatellite markers and at 101 single
nucleotide polymorphisms (SNPs) located within known-function genes. We
identified substantial population differentiation using both marker
types with relatively greater divergence and hence finer population
structure using the microsatellite markers. While population structures
resulting from the two marker types were in general agreement,
functional SNPs showed evidence of stabilizing selection at both global
and population pairwise levels, with a few key SNPs showing signatures
of pairwise divergent selection, consistent with expectations of local
adaptation. The observed complex and inconsistent pattern of pairwise
divergence (selection) at key candidate-gene loci may reflect rapid
environmental change decoupling locally adapted genotypes from actual
local environmental conditions. Our work highlights microevolutionary
changes that are likely to be very important not only in arctic-breeding
songbirds, but in Arctic and Sub-Arctic vertebrates in general, which
are experiencing strong environmental effects from accelerated climate
change and human-induced stressors.