Male and female fruit flies have a common interest in reproduction, but they're at odds on one key point: While every male wants his sperm to fertilize the female's eggs, the female wants only certain males to succeed.
A new study co-authored by a biologist at the University of California, Davis, suggests that the conflict provokes continual tit-for-tat changes in the flies' genes -- a male-female game of leapfrog that could have important evolutionary consequences.
In the study, which appears in the Jan. 8 issue of the journal Science, UC Davis professor emeritus Timothy Prout and two collaborators arranged 6,200 fruit-fly matings and charted the paternity of the 125,000 subsequent offspring. The results revealed a new factor controlling sperm success: The male's genes had to match in certain ways with the female's genes.
In theory, under those conditions, males with the most successful genetic makeups would soon evolve to dominate the population. The researchers suggest that to forestall that happening, females frequently change their genetic profiles to alter the males' competitive odds.
"This sort of interaction could be an important factor for maintaining variation among the successful males," says Prout. "There's a lot of scientific interest in these issues of sexual selection, which occur not just in many insects, but also in some birds and mammals."
Prout's co-authors are Andrew Clark, professor of biology, Pennsylvania State University, and David Begun, assistant professor of zoology, University of Texas at Austin.