Data from: Extensive phenotypic diversification coexists with little genetic divergence and a lack of population structure in the White Wagtail subspecies complex (Motacilla alba)

Geographically clustered phenotypes often demonstrate consistent patterns
in molecular markers, particularly mitochondrial DNA (mtDNA) traditionally
used in phylogeographic studies. However distinct evolutionary
trajectories among traits and markers can lead to their discordance.
First, geographic structure in phenotypic traits and nuclear molecular
markers can be co-aligned but inconsistent with mtDNA (mito-nuclear
discordance). Alternatively, phenotypic variation can have little to do
with patterns in neither mtDNA nor nuclear markers. Disentangling between
these distinct patterns can provide insight into the role of selection,
demography and gene flow in population divergence. Here we examined a
previously reported case of strong inconsistency between geographic
structure in mtDNA and plumage traits in a widespread polytypic bird
species, the White Wagtail (Motacilla alba). We tested whether this
pattern is due to mito-nuclear discordance or discrepancy between
morphological evolution and both nuclear and mtDNA markers. We analyzed
population differentiation and structure across six out of nine commonly
recognized subspecies using 17 microsatellite loci and a combination of
microsatellites and plumage indices in a comprehensively sampled region of
a contact between two subspecies. We did not find support for the
mito-nuclear discordance hypothesis: nuclear markers indicated a subtle
signal of genetic clustering only partially consistent with plumage
groups, similar to previous findings that relied on mtDNA. We discuss
evolutionary factors that could have shaped the intricate patterns of
phenotypic diversification in the White wagtail and the role that repeated
selection on plumage “hotspots” and hybridization may have played.