How capuchino seedeaters have such big differences in plumage despite little genetic diversity

(Bob Yirka 29 May 2017)
A team of researchers from the U.S., Brazil and Argentina has found clues that help explain why southern capuchino seedeaters have such wide differences in plumage despite being so closely genetically matched. In their paper published on the open access site Science Advances, the group describes the genetic analysis they conducted on the South American birds and what they found by doing so.

Southern capuchino seedeaters are a type of song bird, one of a group with familiar finch-like bills. They live in different parts of South America and have evolved in a unique way—the males have widely different plumage coloring and large differences in their songs. Prior research has shown that despite the differences in plumage, the birds are all quite genetically close. This led the team to wonder how or why that might be possible. They devised a theory that suggested that strong selection in an important part of the genome could perhaps lead to such differences. To find out if they were right, they conducted a DNA analysis of 56 individual birds from five species representing different plumages and found their genetic makeup to be nearly identical.

The team then took a closer look at the part of the genome known to be involved in creating melanins, a group of natural pigments. They found that 99 percent of the genome differences between the species occurred in such regions. But because speciation in seedeaters came about quickly, that led the researchers to suggest that it was due to actions by females—by exhibiting certain preferences in plumage or songs, the researchers theorize, the females were causing the males to adapt quickly.

The researchers conclude that natural selection due to female behavior has driven faster-than-normal speciation in the birds, resulting in wildly divergent plumage and song types—similar, they note, to the way the bills of Darwin’s finches have changed to adapt to conditions in the Galapagos. They suggest their work offers new insight into the ways strong genetic processes acting on a few key genes can bring about fast evolutionary changes.

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