Research led by the Cornell Lab of Ornithology and the University of Sheffield in the United Kingdom revealed an evolutionary selection mechanism that causes polymorphism (multiple color types of a single species) in Gouldian Finches. The study, published in April in the journal Nature Communications, identified the mechanism that allows this species to produce individuals with red heads, black heads, and yellow heads.
“Most people have heard of natural selection,” says lead author Kang-Wook Kim at the University of Sheffield. “But ‘survival of the fittest’ cannot explain the color diversity we see in the Gouldian Finch. We demonstrate that there is another evolutionary process, balancing selection that has maintained the black or red head color over thousands of generations.”
The researchers independently zeroed in on the gene found on the Gouldian Finch sex chromosome that regulates melanin to produce either red- or black-headed finches. Rather than competing, the two teams decided to join forces and share their data. For the yellow morph, a different gene not located on the sex chromosome is controlling the head pigmentation, but that gene hasn’t yet been found.
Study coauthors David Toews and Scott Taylor, who worked on the research as postdoctoral researchers at the Cornell Lab, had done similar previous research that revealed the genes likely governing the plumage differences between Blue-winged and Golden-winged Warblers. One of those gene regions is in the same spot on the sex chromosome that differs among Gouldian Finches with different head colors.
“The probability that we’d locate the exact gene region that governs plumage differences in both the Gouldian Finch and the two warblers was almost zero,” says Toews, who is now a professor at Penn State University. “But now that we’ve done it, it opens up the possibility that the same region in other species may also be controlling plumage color.”
Kim, K.-W., et al. (2019). Genetics and evidence for balancing selection of a sex-linked colour polymorphism in a songbird. Nature Communications 10:1852.
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