DENVER--The going theory that males couldn't care less with whom they mate may need an overhaul. New research suggests that males--or at least, male fruit flies--are much more selective about their females than standard evolutionary theory predicts. It's not clear what males are looking for in females, especially because they tend to lack flashy traits such as a colorful tail.
Since the late 1960s, scientists have theorized that the parent who invests more heavily in reproduction will be more selective when choosing a mate. Females do tend to be finicky, apparently because they often have large, energy-intensive eggs, and devote lots of time to caring for their offspring. But few studies have tested whether the opposite holds true for males--whether they're naturally promiscuous when sperm are plentiful and parental investment low.
Presenting 17 February at the annual meeting of the American Association for the Advancement of Science, behavioral ecologist Patricia Adair Gowaty of the University of Georgia in Athens described recent experiments in Drosophila pseudoobscura, a species of fruit fly in which the female egg dwarfs the sperm. She and her colleagues presented individual flies of each sex with two flies of the opposite sex. By observing whether the single fly quickly approached a mate and stayed put, they could measure its pickiness. The researchers found that females and males were equally picky, and that it paid off: Flies that mated with their first choice produced fitter offspring than those made to mate with their second choice. The results echo earlier studies with house mice, which also showed the males to be as picky as females, says Gowaty; ongoing studies in cockroaches and ducks seem to agree as well.
The work suggests that factors besides parental investment may affect mate choice much more than evolutionary theory anticipates, says Robert Warner, an evolutionary biologist at the University of California, Santa Barbara. And such selectivity, Gowaty adds, raises plenty of questions--for one, what are males looking for in their females?