Researchers have claimed that promiscous females act in that manner as nature's way of dealing with inbreeding.

The scientific team from the University of

East Anglia said it witnessed a change in mating behaviour when they bred female flour beetles with their close relatives.

The study, published in Science, helps explain why females throughout the animal kingdom often mate with several males, even though just one is usually enough.

The paper's lead author Professor Matthew Gage said: "These

exciting results show how this common but paradoxical mating pattern

can evolve if females use it to avoid reproducing with genetically

incompatible males."

The researchers showed that

living in a highly inbred population lowers females' breeding success

by about half. But taking lots of mates lets them overcome this

disadvantage, breeding just as successfully as those from a healthy,

diverse population.

Scientists call the behaviour 'polyandry' and say mating

with several males is common in many animals.

Usually, it has

clear costs – reducing reproductive success or even shortening a

female's life – and offers little benefit. In normal circumstances, one

male is enough to let a female make the most of her fertility.


experiment suggests promiscuous behaviour can help females avoid the

harmful effects of belonging to an inbred population – often the result

of a 'genetic bottleneck' in the past, in which all but a small

proportion of a population has been killed off before it can pass on

its genes.

Attempting to explain why unbridled mating was on the

increase, the researchers went on to show that inbred females left

twice as many descendents as those that mated with just one male.

Highly magnified Tribolium sperm fight it out within the female reproductive tract.


is quite easy to imagine how promiscuity could spread through the

population if [promiscuous females] leave more descendents," explained

UEA evolutionary biologist Matthew Gage.

When a

population is inbred, the chances of mating with a genetically similar

male are heightened, so hedging your bets and mating with more suitors

is a sensible strategy, he explained.

Dr Gage suspects

that promiscuous females amass a large pool of sperm, and select ones

that are more genetically dissimilar to them to fertilise their eggs.

Mating with more males gives females a larger range of sperm from which

to select.

However, Dr Gage warned that he and his colleagues might not have witnessed "the evolution" of a new mating behaviour.


than changing genetically, he explained, the females might simply have

been adjusting their behaviour to their new environmental conditions.

Dr Gage and his team are now looking into this.