Ecologists uncover biological benefits of sleeping around

Females have traditionally been viewed as the choosy, monogamous sex compared to males, but recent genetic studies have revealed that females of many, if not most, animal species also mate multiply with different partners. However, understanding why females should do this has remained something of enigma.

Speaking at the British Ecological Society’s Annual Meeting, Dr William Hughes of the University of Sydney and Professor Jacobus Boomsma of the University of Copenhagen will announce the results of their experiments with Panamanian ants, which show that mating with many different males (polyandry) produces colonies that are more resistant to disease. According to Hughes: “This study shows that genetically diverse groups of social insects are more resistant to disease than genetically homogenous groups.”

Sex is a costly business for most animals, using precious energy and exposing the female to the risks of being predated or of catching a disease, notably those that are sexually transmitted. For many species ecologists don’t yet understand why females should engage in this costly behaviour because it has been hard to identify how the female benefits.

Using colonies of Panamanian leaf-cutting ants, which are highly polyandrous, Hughes and Boomsma used genetic markers to identify the fathers of particular ants. They then created small groups of genetically diverse ants (simulating colonies that result from queens that mate with multiple males) and of genetically homogenous ants (simulating colonies resulting from queens that mate with single males). They then studied which groups survived better after being infected with a virulent fungal parasite.

“The results of our study suggest that social insect queens may benefit from mating with multiple males by making their colonies more genetically diverse and therefore more resistant to disease. This indicates females can get genetic benefits simply by mating with many males, as compared to going through the laborious process of choosing males. The results suggest one reason why some of the largest and most complex insect societies appear to suffer so little from disease,” Hughes says.

Dr Hughes will present their full findings at 09:00 on Wednesday 8 September 2004.