Beetles mount a strong case for gay behaviour

Biologists have found an evolutionary explanation for homosexual behaviour - at least in a species of beetle where members of the same sex frequently copulate.

Biologists have found an evolutionary explanation for homosexual behaviour - at least in a species of beetle where members of the same sex frequently copulate.

A study of Diaprepes abbreviatus , an inch-long American beetle known as the sugarcane rootstalk-borer weevil, found "lesbian" behaviour attracts bigger male suitors. Ally Harari, a biologist at Ben-Gurion University in Israel, and Jane Brockman, professor of zoology at the University of Florida in Gainsville, say: "By mounting each other, the females are able to attract more attention from larger males than if they were seeking males alone."

Their study, published in Nature , shows smaller males are apparently put off by the size of the top female, which is usually the larger sex. Biologists have often observed homosexual behaviour in several species. The standard explanation, for instance in domesticated cows which mount each other, is that it is a display of dominance.

The beetle researchers stuck dead females of varying sizes to the backs of living ones and found large males were attracted to larger copulating females. Apparently, male beetles are not good at distinguishing between copulating females and a heterosexual pair.

Professor Brockman said females who mount each other are actually improving their reproductive success. "Larger males are advantageous because their size may indicate their ability to find food, or large males may transfer valuable resources to the female," she added.

Studying the phenomenon in the wild is difficult, because although males will mount females for up to 10 hours, female copulation averages less than 10 minutes - which is why the scientists had to use the glue.

Their next goal is to find out why male beetles engage in homosexual behaviour.