Golden-crowned and white-crowned sparrows have been hypothesized to have undergone rapid, and relatively recent (~50,000 years ago) speciation because they have nearly identical mitochondrial genomes. Nonetheless, the two species display distinct plumages, breeding behaviours, and songs, and appear to be reproductively isolated in their extensive areas of breeding range overlap.
An alternate hypothesis to explain their similar mitochondrial genomes proposed speciation in the more distant past, but with subsequent hybridization and mitochondrial introgression (where new hybrid individuals mate with individuals from the parental species). Research supporting this hypothesis has previously lacked robust nuclear gene trees to distinguish between introgression and incomplete lineage sorting.
In a recently published paper, former Queen’s Biology postdoctoral fellows Dr. Rebecca Taylor, and Dr. Rute Clemente-Carvalho, former BSc thesis students Ashley Bramwell and Katherine Dares, former PhD Student Dr. Nick Cairns, Associate Professor Dr. Fran Bonier, and Professor Dr. Steve Lougheed investigate opposing hypotheses (rapid speciation hypothesis vs. hybridization hypothesis) regarding golden-crowned and white-crowned sparrow divergence. They investigate speciation and introgression using two different genetic tools, mitochondrial DNA (mtDNA) sequencing and a genome-wide panel of nuclear Single Nucleotide Polymorphisms (SNPs).
Taylor et al. find that golden-crowned and white-crowned sparrows are deeply divergent in their nuclear DNA, and that the difference seen in the mtDNA is best explained by historical hybridization and mitochondrial introgression (supporting the hybridization hypothesis). They also find evidence that the white-crowned sparrow subspecies comprise two distinct clades. The authors conclude that nuclear sequencing (SNPs), or a combination of mtDNA and SNPs, is a more powerful tool for discovering divergence mechanisms.
To learn more, read their article in Molecular Phylogenetics and Evolution.
