New research out of the University of Missouri shows that when it comes to female mate preference in a certain species of tree frog, there may be more than meets the eye. Females may actually prefer the calls of males that share the same number of chromosomes.
Carl Gerhardt, curators professor of biology at MU, and his graduate student, Mitch Tucker, study two closely related species of tree frog: the Cope's grey and the eastern grey. The latter species has twice as many chromosomes as the Cope's, but the two remain nearly identical. And the only real way to tell them apart is through their calls. The Cope's grey tree frog has a faster call, while the eastern grey's is slower.
"A great comparison is a fast talking New Yorker, compared to a southern Georgia drawl," says Tucker. "Saying the same sentence, saying the same word, just the words come out of the mouth at a slower repetition."
From a previous experiment, Gerhardt knew that increasing the chromosome number in male Cope's grey tree frogs made their calls more closely resemble the eastern grey's. But would females respond to that call?
To find out, Tucker took female Cope's grey tree frogs with an extra chromosome set, and tested a series of artificial calls: one resembled the slower call of the eastern grey, while the other was faster, similar to the Cope's. And what he discovered was that females actually preferred the calls corresponding to a higher chromosome number.
Gerhardt says that this dual shift in male calls and female preference may have contributed to the success of the eastern grey when it first emerged as a species. He says he hopes to study the mechanisms underlying this shift in female mate preference.
Correction: The audio version of this story suggests that humans underwent polyploidy. It actually occured in the early history of the vertebrates.
