Some female mammals turn promiscuous to protect offspring

In mammal species among which infanticide by males is common, females turn promiscuous as part of strategy to confuse paternity and protect their offspring, a new study says.

Infanticide by males is widespread in many mammal species.

When a rival male takes over a group, he will kill the infants of previously dominant males to render the females "sexually receptive" again, so that he can sire his own offspring.

In some species of mammals, females do not come into season again while they are lactating and nursing young ones.

However, the females of some species - such as the mouse lemur - have evolved a highly-effective counter-strategy to stop males from killing their offspring: They mate with as many males as possible in a short time, the study noted.

By confusing the paternity of the infants with the help of a process known as "paternity dilution", any act of infanticide committed by the male raises the possibility of he killing his own offspring.

In such species, reproductive competition shifts to after copulation, not before - so that the most successful male is the one whose sperm outcompetes those of the others.

This leads to males producing ever larger quantities of sperm, leading in turn to increase in testes' size. The testes of male mouse lemurs swell 5-10 times larger during the breeding season.

"In species in which infanticide occurs, testicles size increases over generations, suggesting that females are more and more promiscuous to confuse paternity," said lead author Dieter Lukas from the University of Cambridge in Britain.

"Once sperm competition has become so intense that no male can be certain of his own paternity, infanticide disappears - since males face the risk of killing their own offspring and might not get the benefit of siring the next offspring," Lukas added.

The study appeared in the journal Science.