When it’s mating season for white-crowned sparrows, even mountains aren’t in the melodious birds’ way.
Populations in British Columbia and Alberta, on the east and west sides of the Rocky Mountains, share a lot of genes, explained Catherine “Cat” Welke, a master of science candidate at the University of Lethbridge. Welke has been researching barriers to gene flow in white-crowned sparrows, and presented her results at Waterton-Glacier Science and History Day last week.
Although east and west side populations have DNA in common, birds separated by large geographical distances don’t have nearly as many of the same genes. This could help explain why the sparrow is already classified into five subspecies.
Welke’s work focused on isolation as mechanism for genetic change in populations. For changes in DNA to occur over time, organisms must be physically separated by distance, landscape features, micro-climates like those found along an alpine slope, or behavioral differences - anything that prevents breeding between discrete populations.
The white-crowned sparrow inhabits much of North America and can be found from sea level to mountain elevations. The three subspecies Welke studied were the Puget Sound type, found in the Pacific Northwest, and the Gambel’s and mountain types, found in Canada and the U.S. Rockies, respectively.
Welke used mist nets to capture the birds in the field, took a few drops of blood, and released them. She used their mitochondrial and nuclear DNA to compare genes, because these types of DNA take thousands of years to be affected by evolution.
Although she also conducted elevation transects in Oregon and Colorado, she found that the populations’ genes didn’t change as elevation increased.
Welke found that physical distance was the greatest barrier to interbreeding between populations, and that genetically, the Oregon and Colorado birds are pulling away from the Canadian birds. The Puget Sound type, particularly, doesn’t migrate as far as other subspecies, she noted.
But as for the British Columbia and Alberta birds, they showed about half of the same DNA, suggesting that the birds easily traverse the mountains to reproduce. However, the southern Alberta birds, mostly those in the Waterton Lakes area, had more unique DNA than the northern Alberta birds or the British Columbia birds.
In future work, Welke hopes to reveal an explanation for why this is, as well as identify specific landscape barriers to gene flow.
Welke noted that her project was inspired by similar work on other bird species. Such studies can help explain the development of new species over time as populations become more genetically isolated. Historical modeling of sparrow habitats is also in Welke’s future, she said, which will allow her to make predictions about new habitats in response to climate change.