Lausanne, Switzerland - Playing the field apparently has evolutionary advantages.

According to a study by two biologists at the University of Lausanne in Switzerland, male fruit flies from a long line of monogamous sires show less intelligence than those whose progenitors competed with rivals for multiple females' favours.

They said the results provide “direct experimental evidence for the hypothesis that competition for mates is a major force driving the evolution and maintenance of cognitive performance in animal species.”

Brian Hollis, a postdoctoral researcher, and Tadeusz Kawecki, an associate professor, imposed strict monogamy on three replicate populations of the fruit fly Drosophila melanogaster for over 100 generations by randomly pairing virgin males and virgin females in vials, where they were allowed to spend two days mating.

In three polygamous control populations, meanwhile, the scientists placed groups of five virgin females and five virgin males for two days in vials.

From the mated females' eggs came each successive generation of fruit flies, which have a life cycle of less than two weeks at room temperature.

Females are able to mate about 12 hours after emergence from their pupal case and lay hundreds of eggs within a few days.

After more than 100 generations, Hollis and Kawecki compared the mating behaviour of the monogamous and polygamous populations, the study, published in the British Royal Society's biological-research journal Proceedings B, reports.

When they got access to females that behaved like ordinary wild flies, males from a monogamous population sired far fewer offspring than males from a population that had remained polygamous.

The scientists found the males were not even good at spotting females that had already mated and were no longer receptive.

They not only took up to 75 percent longer to achieve copulation, but flunked a test of whether they could learn to associate a certain smell with danger. - Sapa-dpa