Blue-winged, golden-winged warblers not all that different

After over 10 years of trying to determine genetic differences between golden-winged and blue-winged warblers, researchers discovered some surprising information.

In a study published in the journal Current Biology, a research team sequenced complete genomes of both birds and found they were 99.97 percent alike. This could have some implications on the conservation status of the golden-winged warbler (Vermivora chrysoptera), which has declined by 66 percent since 1968, according to the North American Bird Breeding Survey.

The golden-winged warbler is listed as threatened under Canada’s Species at Risk Act. In the U.S., however, the species isn’t federally protected although it has been proposed for listing in the past. There’s some confusion about federal protection due to hybridization with blue-winged warblers (Vermivora cyanoptera), says David Toews, a postdoctoral researcher Cornell University’s Lab of Ornithology and co-lead author of the study.

For a long time, Toews, his co-lead author Scott Taylor and their colleagues from the evolutionary biology group at the Lab of Ornithology tried to find a genetic marker that differed between the two warblers in order to develop a hybrid index for conservation managers. However, the researchers had difficulty finding those differences. In fact, a year and a half ago, Toews and his colleagues carried out what they considered “the latest and greatest genomic analysis of the group.” “And we still came up with nothing,” Toews says. That was surprising because even in populations of the same species such as chickadees, there are often thousands of differences. “At that point, we were getting a little frustrated.”

But recently they made headway in their search for that “needle in the genomic haystack,” Toews says. After catching 20 golden-winged and blue-winged warblers in the spring of 2015 in areas around New York, the researchers took blood samples and completed whole genome sequencing of both species.

Their analysis revealed barely any genetic differences between the two — except for a handful of variations in plumage such as the color of the species’ throats. “We were excited by these results,” Toews said.

Further, the team measured the genomic differences between the two warbler species in a fixation index or FST, which is a measure that ranges from 0-1 where “0” represents no difference in genomes while “1” is the equivalent of 100 percent. The difference between the two types of birds was 0.005, according to Toews.

They then extended the sampling to almost 350 birds including Brewster’s warblers and Lawrence’s warblers, which are hybrids of golden-winged and blue-winged warblers, looking at a smaller portion of the genome. Their research showed that Brewster’s warblers seem to be an expression of dominant traits and Lawrence’s warblers showed more recessive traits.

Toews says these findings may have some conservation implications, especially regarding listing the golden-winged warbler under the Endangered Species Act. “There will likely be challenges to whether these two birds are in fact distinct species,” he said. “And I think when the rubber hits the road this can have conservation implications and funding implications too, just because while in theory money can go to groups below the species level, in many ways the focus is usually on distinct species.”

In fact, researchers recently raised similar conservation questions regarding the hybridization of eastern and red wolves.

Further, while hybridization is often facilitated by anthropogenic habitat change, Toews and his colleagues created a computational model that showed the hybridization of these two birds was likely going on for quite some time.

“The management implications have been to manage habitat to reduce hybridization,” he said. However, Toews says if what they’re saying is true, it’s likely that different dynamics have caused this hybridization to happen before. “It’s tough and we don’t know what’s going to happen in the future. It’s kind of a challenging question going forward.”