  Generally, genotypes and phenotypes are expected to be spatially congruent,
however, in widespread species complexes with few barriers to dispersal,
multiple contact zones, and limited reproductive isolation, discordance between
phenotypes and phylogeographic groups is more probable. Wagtails (Aves:
Motacilla) are a genus of birds with striking plumage pattern variation across
Eurasia. Up to 13 subspecies are recognized within a single species, yet
previous studies using mitochondrial DNA have supported phylogeographic groups
that are inconsistent with subspecies plumage characteristics. In this study,
we investigate the link between phenotypes and genotype by comparing
populations thought to be at different stages along the speciation continuum.
We take a phylogeographic approach by estimating population structure, testing
for isolation by distance, conducting demographic modeling, and estimating the
first time-calibrated species tree for the genus. Our study provides strong
evidence for species-level patterns of differentiation in wagtails, however
population-level differentiation is less pronounced. We find evidence that
three of four widespread Eurasian species exhibit an east-west divide that
contradicts both subspecies taxonomy and phenotypic variation. Both the
geographic location of this divide and time estimates from demographic models
are overlapping in two sympatric species, indicating that coincident
Pleistocene events shaped their histories.
