A study from scientists in the University of Exeter shows the changes happen over generations.
Males and females who have too much sexual intercourse could see a change in the shape of their genitals, according to a new study.
The research involves burying beetles, and offers evidence that mating can cause males to grow longer penis-like organs and females larger ‘claws’ on their genitalia.
The changes can show within ten generations of beetles, according to scientists at the University of Exeter .
Genital shape varies enormously across the animal kingdom compared, for instance, to body shape.
The paper, published in the journal Evolution, suggests this is because shapes of male and female genitalia co-evolve as a result of what they term 'sexual conflict'.
Author Dr Megan Head said: “It takes two to tango, so when changes in shape in one sex leads to corresponding changes in the other sex this is known as co-evolution.”
Although males benefit from mating, as it increases the number of offspring they are likely to produce, it's negative for females, because they only need to mate a few times to fertilise all their eggs.
In addition too much sex can be costly for female burying beetles as it reduces their ability to provide parental care.
To test whether sexual conflict could lead to co-evolutionary changes in the shape of genitals, researchers artificially selected pairs of burying beetles for either high mating rates or low rates for ten generations.
The research found that this artificial selection resulted in changes in the shapes of both male and female genitalia.
It also found that changes in one sex were reflected by changes in the shape of the other sex, showing there was co-evolution.
The greatest changes in shape occurred in beetles selected for high mating rates, where sexual conflict was greatest: males evolved to have longer intromittent organs - penis-like structures - and females responded by evolving more pronounced ‘claws’ on their genitalia.
Dr Paul Hopwood, of the University of Exeter, reveals: “Although we don’t know the ins and outs of how these genital structures relate to the reproductive success of each sex, our results show that sexual conflict over mating can lead to co-evolutionary changes in the shape of the genitals of burying beetles.”
“Our research demonstrates the general importance of conflicts of interest between males and females in helping to generate some of the biodiversity that we see in the natural world.
"It’s fascinating how genital evolution can happen so fast – in ten generations – showing how rapidly evolutionary changes can occur.”