RESULTS
We generated genomic data for 9 individuals breeding in coastal North
Carolina (putative S. v. waynei) , and 20 individuals from the
nominate subspecies, S. v. virens , which were distributed across
their breeding range. Genome-wide F ST indicated
low (0.027) overall differentiation across the S. virens complex.
However, principal component analysis revealed three highly clustered
groups, one of which consisted of only S. v. waynei (Figure 2).
Samples from coastal North Carolina (S. v. waynei) were distinct
along PC1, which explained 8% of the total variance in the data, and
strongly separated from S. v. virens . Samples of S. v.
virens from the Uwharrie National Forest in central North Carolina
separated along PC2 (4.1% variance) with the remaining group composed
of S. v. virens samples from Arkansas, Tennessee, Indiana, and
New York (Figure 2).
Differentiation was not homogenous across the genome (Figure 3A). We
identified two regions of the genome, one on chromosome 6 (Figure 3B)
and one on the sex (Z) chromosome (Figure 3C) that showed elevated
differentiation above the background. On chromosome 6, the elevated
region spanned 16,950,000bp and 17,040,000bp (a length of 80,000bp) and
had six windows with F ST above 0.15 (the maximum
windowed F ST in this region was 0.28). The region
on the Z chromosome, between 11,910,000bp and 12,150,000bp (a length of
240,000bp) contained 10 windows above F ST 0.15
(the maximum windowed F ST in this region was
0.32). The chromosome 6 region included five annotated genes that were
bounded by the region of elevated divergence; the Z chromosome region
had four annotated genes, and one gene of unknown function (Figure 4).
Phylogenetic relatedness among the samples clustered most samples by
geographic locality (Figure 5). The initial split within the species
occurred between samples from New York and other samples from southern
populations. Samples from putative S. v. waynei formed a
monophyletic group, which was sister to birds breeding in the Uwharrie
National Forest of central North Carolina.