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
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,
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
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.
is quite easy to imagine how promiscuity could spread through the
population if [promiscuous females] leave more descendents," explained
UEA evolutionary biologist Matthew Gage.
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
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.