Creating hybrids by crossing closely related species of plants is common pratice in horticulture, but when it comes to chorus frogs such hybridizations can be maladapative, a new study shows.

At the ongoing Evolution 2010 meeting in Portland, Oregon, evolutionary biologist Emily Moriarty Lemmon from Florida State University in Tallahassee impressed her colleagues with the results of her chorus frog hybrid study. She and her husband/collaborator Alan Lemmon (collectively they are known as “the Lemmons”) estimated the fitness of hybrids of the chorus frogs Pseudacris feriarum and Pseudacris nigrita, who coexist in the southeastern US. They crossed these two species and raised the offspring in the lab until sexual maturity. The Lemmons studied the viability, mating success, and fertility across the life cycle of their hybrids and found their fitness was reduced by 44% compared to their parent species. The decline was the result of females selecting against hybrid males as well as natural selection on male fertility. In other words, fewer females wanted to mate with the male hybrids, and those that did often got poor results. Ultimately, says Lemmon, this drives the two closely related speices toward reproductive isolation. “Hybridization is costly,” she says.

Nearly 2,000 researchers coverged on the Evolution 2010 meeting this year where, unlike most professional gatherings, enthusiastic conversations about animal sex are quite all right.

Image: chorus frog / John White