An incredibly rare hybrid warbler with mismatched color patterns allowed researchers to unravel the genetic factors of two traits that typically come as a package: the black face mask and the black patch on the throat in blue-winged and black-winged warblers. golden wings. New study describing the particular bird and locating the location in the genome that controls the face mask and throat patch appears online in the journal Ecology.
“Golden-winged warblers have both a black face mask and a black throat patch, while blue-winged warblers have neither,” said Marcella Baiz, postdoctoral researcher at Penn State and first author of the study. “When individuals of each species mate, almost all of their hybrid offspring have paired traits, so either both black plumage traits are present or both are absent. But we have captured this very strange bird that looks almost entirely like a golden-winged warbler but lacks the black patch on the throat. “
Researchers believe this unique combination occurs in less than 0.5% of hybrid warblers. To their knowledge, this type of hybrid had only been previously documented in a bird collected in 1934 and described in 1951 in a museum collection.
“We originally found this bird on advice from a local bird watcher who works at Shaver’s Creek Environmental Center,” said David Toews, a professor of biology at Penn State and author of the study. “He suggested that a nearby area appeared to be good habitat for warblers and also uploaded warbler sightings to the eBird app, which scientists can use in their research. We went to explore the location when we got there. spotted this unique and exciting bird. We carefully captured the bird so that we could document its plumage, take a blood sample to sequence its genome, and then release it. “
In a previous study, researchers sequenced the genomes of blue and golden-winged warblers and their hybrids and identified a small region that causes black staining in these birds upstream of the Agouti signaling protein (ASIP) gene. But since the two traits are almost always inherited together, it was not clear whether ASIP regulated the traits together or separately.
“Because we already had genome sequencing data from parental species and hybrids with matching face and throat color, sequencing of the unpaired bird genome allowed us to separate the underlying genetic regions. of the face mask versus the throat patch, âBaiz said.
The team confirmed that the previously identified region is connected to the black throat patch, and also identified a new location – nearby, but further upstream in the genome – that they believe is connected to the black face mask. In order for the black pigment to occur in these birds, both copies (one on each chromosome) must originally come from the Golden-winged Warbler, suggesting that these are “recessive” traits. Having one or both copies of the Blue-winged Warbler in these locations does not result in any face masks or throat patches.
âOver a hundred years ago, a biologist named John Treadwell Nichols hypothesized that the black throat stain was a recessive trait,â Toews said. “Later, when Kenneth Parkes described the rare hybrid in 1951, he suggested that if the throat and mask color were controlled separately, they should be related in some way or located very close to each other. on the genome. Parkes described his theory as a “genetic problem for future study,” and we were able to confirm both theories using modern genetic tools. “
The researchers suggest that the locations they identified could be located in two separate promoter regions for the ASIP gene, which turn the gene on or off in different contexts. Because they are located so close to each other on the chromosome, promoters would generally be inherited together, even if genetic material is mixed between chromosomes during reproduction, which would explain why most hybrids carry both or neither. of those features of black plumage. The mismatched bird, however, was likely the result of an extremely rare case where this was not the case, followed by several generations of backcrosses with golden-winged warblers.
“If the staining genes in warblers have a similar genetic architecture, with multiple promoters controlling where the pigment is deposited, it is easy to see how a few mutations could produce a variety of different color patterns among these species. ‘songbirds,’ Baiz said. “It may help explain why there are so many different species of warblers with such diversity in color.”
Since the coloring of a warbler is an important clue to behaviors such as mating, it is possible that the incompatible hybrid carries only one of the traits. For example, it may be attractive to females of both species because it possesses the qualities of both or one or the other. Researchers hope to observe this bird in the future and determine if it has a mate, and future research linking plumage traits to reproductive success would clarify these implications.
âWe have now observed this bird for two years in a row, so it has survived at least two migration events,â Toews said. “This study and the story of how we found this bird is a great example of how birders and citizen scientists can make a real difference in research.”
What determines the colors of a warbler?
Marcella D. Baiz et al, Rare hybrid solves the “genetic problem” of related plumage traits, Ecology (2021). DOI: 10.1002 / ecy.3424
Provided by Pennsylvania State University
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