Genomic and Mitonuclear Patterns of Divergence Among Recently Diverged White-Crowned Sparrow Subspecies

Genetic divergence and subsequent speciation are possible within the range and habitat of a population. White-crowned sparrows are comprised of five subspecies that thrive in a wide range of habitats, latitudes, and elevations across North America, suggesting the ability for local adaptation and rapid divergence. We assessed genome-wide genetic differentiation in four populations of white-crowned sparrow (Zonotrichia leucophrys gambelii, Z. l. oriantha (northern and southern), and Z. l. pugetensis) and compared patterns of genetic structure using outlier single nucleotide polymorphisms (SNPs), including mitochondrial (255 SNPs) and Z chromosome (580 SNPs) loci. When these four populations are assessed using the full SNP dataset, three genetic clusters are identified: pugetensis, southern oriantha, and northern oriantha grouped with gambelii. However, four genetic clusters are supported by the Z chromosome outlier SNPs corresponding to three subspecies and a north-south split in Z. l. oriantha. Our analyses pointed to consistent divergence of Zonotrichia leucophrys pugetensis from other populations and mitochondrial SNPs showed overlap of southern Z. l. oriantha and Z. l. gambelii. Interestingly, northern Z. l. oriantha populations are more genetically similar to Z. l. gambelii as opposed to its sister population, the southern Z. l. oriantha. We found a region on the Z chromosome with highly elevated F _ST among all the populations. The genetic clusters identified in our study may be suggestive of evolutionary events such as selection on the Z chromosome, and this may be driving divergence in white-crowned sparrows.