New research has shown that the presumed extinct Bachman's Warbler was a full species.
Bachman's Warbler was last seen in North America some 40 years ago, with the last widely accepted sightings in the 1960s. Although not yet officially recognised as Extinct by IUCN, the species is widely believed to have been lost for good.
The species was closely related to Blue-winged Warbler and Golden-winged Warbler. A new study, published in Current Biology, has confirmed via genome sequencing that Bachman's Warbler was a distinct species.
Bachman's Warbler is one of the most enigmatic North American birds. It is widely considered to be extinct (Louis Agassiz Fuertes).
During the research the full genomes of seven museum specimens of the bird were sequenced. The genome comparisons of Bachman's Warbler with Golden-winged and Blue-winged Warblers also helped researchers identify a new candidate gene involved in feather pigmentation in the group.
"Bachman's Warbler is the only songbird known to have recently gone extinct in North America," said David Toews, assistant professor of biology in the Penn State Eberly College of Science and the leader of the research team. "It is one of three species in the genus Vermivora. Our lab studies the two living species of this genus, which are known to mate with each other producing hybrid offspring."
Golden-winged and Blue-winged Warblers produce a spectrum of hybrids, but two distinct types of hybrid offspring, each with a unique combination of the parent species' colouration, have been the focus of ornithologists. This is because these two hybrids were once thought to be distinct species themselves – Brewster's Warbler and Lawrence's Warbler – until careful study of wild hybrids and, now, modern genetic analysis has confirmed their hybrid origins.
The extinct Bachman's Warbler resembles one of these hybrid offspring in colouration, so there was some question as to whether the Bachman's Warbler was itself a distinct species or if it might also have been a hybrid.
The research team collected seven specimens of Bachman's Warbler from museum collections and extracted DNA from the birds' toepads. They then performed whole-genome sequencing to compare the warbler genome to existing genomes for the two living species in the genus. The genomes of Golden-winged and Blue-winged Warblers are very similar to each other, except for a few regions that are involved in determining the colouration patterns of the bird's feathers. In comparison, the Bachman's Warbler genome was very different, which indicated to the researchers that it was, in fact, a distinct species.
The researchers also compared the genomes of the three species to look for regions of the genome that may have evolved differently in each lineage. These differences can be indicators that a particular region of the genome evolved via natural selection for a particular trait or because of another evolutionary process. Having a third species' genome to compare allowed the researchers to identify a region that contained a new candidate gene involved in warbler pigmentation.
Reference
Wood, A W, Szpiech, Z A, Lovette, I J, Smith, B T, and Toews, D P L. 2023. Genomes of the extinct Bachman's warbler show high divergence and no evidence of admixture with other extant Vermivora warblers. Current Biology, 2023; DOI: 10.1016/j.cub.2023.05.058
