UNIVERSITY PARK, Pa. — A new study has narrowed down the region of the genome that drives the black color in throat and face of warblers by studying the hybrid offspring produced when two species mate. The hybrids of golden-winged and blue-winged warblers have a mix of coloration from the parent species, which allows researchers to identify which regions of the genome are associated with which color patterns. The study, led by researchers at Penn State, also reveals a more complex basis for the amount of yellow in warbler bellies and raises concerns about how hybrids of these species are classified.
Their results appear online in the journal The Auk: Ornithological Advances.
“The distinct plumage of these otherwise very similar birds has perplexed ornithologists for more than a hundred years,” said Marcella Baiz, postdoctoral researcher at Penn State and first author of the paper. “Our research team previously compared the genomes of golden-winged and blue-winged warblers and identified 6 regions that differed between them, some of which may control color. In this study, we used hybrid birds of these species, which mix and match the features of their parent species, to help identify which regions of the genome are associated with which color patterns.”
Color is an important cue for warblers and is prominently displayed during mating and other behaviors. Blue-winged warblers have yellow throats and bellies, while golden-winged warblers have white bellies and a black throat patch and face mask. Hybrids of these species vary in amounts of yellow and whether they have a black face mask and throat, and these characteristics are commonly used to categorize birds into different classes of hybrids.
The research team rated hybrid birds based on their plumage color and genetic likeness to the two parental species. They found that the amount of yellow in hybrids, which is produced by pigments called carotenoids, is not directly related to a bird’s genetic likeness to the parent species — for example, hybrids with more yellow were not genetically closer to blue-winged warblers. Additionally, the extent of yellow in hybrids re-captured in subsequent years appeared to decline over time.