May 20, 2016
Sexual conflict between males and
females can lead to changes in the shape of their genitals, according to
research on burying beetles by scientists at the University of Exeter.
The study, published today in the
journal Evolution, provides new evidence that conflict over how often
mating takes place can lead to males evolving longer penis-like organs
and females larger
'claws' on their genitalia, within ten generations.
Genital shape varies enormously
across the animal kingdom compared, for instance, to body shape. One reason for
this may be that the shapes of male and female genitalia co-evolve as a result
of sexual conflict. Dr Megan Head, one of the authors of the new study 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."
Sexual conflict over mating
occurs because, whilst having lots of sex is usually good for a male—as it
increases the number of offspring he is likely to produce—it is not so good for
a female because she only needs to mate a few times to fertilise all her eggs.
In addition too much sex can be costly for female burying beetles as
it reduces their ability to provide parental care.
In order to test whether sexual
conflict could lead to co-evolutionary changes in the shape of genitals the
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.
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