The patterns – and paradoxes – of female
infidelity was at the centre of the Macquarie
study of the Gouldian finch.
Image: courtesy of Macquarie University
For years, researchers studying the mating behaviour of birds have been stymied by one question: Why would females cheat on their mate – especially when she has a lot to lose if her infidelity is discovered.
Macquarie University biologists Dr Simon Griffith and Dr Sarah Pryke
recently solved this long-standing puzzle and have published their
findings this week in the prestigious international journal Science.
While
most birds, like humans, form partnerships to rear their offspring,
researchers have long known they have the occasional fling. But why they
do it has previously been difficult to establish because females are
especially sensitive to being caught out and will go to great lengths to
hide their behavior from their male mates, according to Griffith.
“They
have a lot to lose if caught with another male so we were intrigued to
find out why the female would run such a risk since the costs of
cheating are quite high,” he said.
As in humans, male partners
play an active role in assisting a female bird to raise her young,
contributing up to 50 per cent of care involved in incubating the eggs
and feeding the offspring. A male who feels he has been cheated on can
reduce the care that he gives or even desert an unfaithful female.
To
solve the puzzle of how and why females gain from a little bit of
infidelity, Griffith and Pryke focused their attention on the Gouldian
finch, a species which they are studying in the tropical savannahs of
Northern Australia and also in captivity.
During a regular
breeding season, the female Gouldian finch will copulate two to four
times a day with her partner. However when given the opportunity in an
experiment, all females willingly engaged in one copulation with an
extra-pair male, irrespective of the quality of their own mate.
Whilst
this does not appear very discerning, the important part was what
happened after that copulation, Griffith said. If the extra male was
genetically better than her own partner then, with just one copulation,
he could fertilise over 75 per cent of her eggs.
“The female is
apparently able to select out genetically good sperm from bad sperm very
effectively. This means that by occasionally cheating, she is
maximizing her chances of having healthy offspring because one
copulation with good male sperm is better than 30 copulations with bad
sperm. So even a little cheating can have big benefits,” he said.
The
intriguing explanation Griffith and Pryke finally confirmed in their
research was that the female finch is actually quite selective in her
infidelity – and from a genetic standpoint, for good reason.
“Our
work suggests that with this mechanism, it would pay most female animals
to cheat on their partner once or twice to insure against any genetic
incompatibility or infertility that their partner might have,” Griffith
said.
Simon Griffith and Sarah Pryke are ARC Research Fellows with
the Department of Biological Sciences.
For more information, visit
the website
in text here
Editor's Note:
Original news release can be found here.
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