Variations in the physical appearance of male barn swallows plays a role in their choice as mates for females — and also fills a gap in understanding how species evolve, led by University of Colorado Boulder researchers.
The experiment, run simultaneously in Colorado and Israel, captured barn swallows and used clippers and non-toxic markers to vary the appearance of males’ breast color and the length of outer tail feathers, while a control group remained unaltered.
Then scientists used DNA testing to measure subsequent reproductive success to determine whether the males’ “new outfit” had an impact. They found that it did: the Colorado birds with darkened plumage and shorter outside tail feathers were most successful, while researchers in Israel found that to be the case in birds with dark breast feathers and longer tail feathers.
“We’ve long known that ecological differences play a role in speciation,” said CU associate professor Rebecca Safran, lead author of the study. “But this is the first experimental evidence to demonstrate the important role of mate selection.”
The “new twist,” added Safran, of CU’s Department of Ecology and Evolutionary Biology, is that trait differences in closely related populations are driven by female choice. Results of the study, funded in part by the National Science Foundation and the Israel Science Foundation, were published in the journal Evolution.
CU researchers collaborated with those at Tel Aviv University in Israel.
