'Female promiscuity nature's way of dealing with inbreeding'

Researchers at the University of East Anglia found that in inbreeding populations the female becomes more promiscuous to screen out sperm from genetically incompatible males.

In a study of flour beetles, the team found the breeding success of females in regular populations was identical, whether mating with one male or five.

However, when they conducted the same tests with an inbred population, females mating with just one male showed a 50 per cent reduction in the number of surviving offspring produced, the Daily Mail reported.

"Polyandry" -- where a female's eggs are fertilised by multiple fathers  -- is the norm in most species, from chimpanzees to chickens, the scientists said.

The results, they said, showed that females possess mechanisms that allow them to filter in the genetically most compatible sperm to produce more viable offspring.

The team then deliberately created "genetic bottlenecks" of inbred beetles and found that after 15 generations the females began to mate more frequently and with more partners.

Lead researcher Prof Matthew Gage said: "By generating inbred populations, we were able to create real risks of high genetic incompatibility between reproducing males and females, and expose the mechanisms that females possess to promote fertilisation by the most compatible males and their sperm.

"These exciting results show how this common but paradoxical mating pattern can evolve if females use it to avoid reproducing with genetically incompatible males."

According to Prof Gage, exactly how females filter the most compatible sperm is not yet understood.

He said: "They might simply mate more frequently, and allow the 'best sperm to win', which would work if winning sperm are from males who have themselves avoided inbreeding depression.

"Or they might choose to mate most with the less related males, perhaps using olfactory cues, thereby concentrating their sperm stores from those males.

"We think that the process occurs most likely at the gamete level, because females mate with most of the males they are exposed to and only store for fertilisation a tiny proportion of the sperm they are actually inseminated with."

Prof Gage pointed out that in many breeding programmes females are made to mate with different males individually to ensure genetic diversity.

But he said it may be better to let nature take its course, as the study indicated females adapted their behaviour to maximise the chances for their offspring.