Female Antarctic fur seals disrupt the traditional notion that the males of a species do all the work in attacting a mate. The females traverse crowded breeding grounds to find a male unrelated to them - in order to prevent inbreeding and give their offspring a leg up.

Credit: Wikimedia

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PARIS: It’s long been thought that males of most species do all the work to attract a mate, but to prevent inbreeding female Antarctic fur seals travel to seek the perfect partner - while males just laze around.

A leading theory about mating displays among animals - and arguably humans, too - is that the males do all the hard work, flashily showing off their fitness to be a breeding partner. The females are passive, letting the males strut their stuff, finally making a choice on the finest display of male strength or dominance.

But Antarctic fur seals have given this stereotype a gigantic wack of their flipper, scientists reported today in the British journal Nature. In this species, the males lie around passively while females jaunt off to find a mate, seeking out a male which is least likely to be genetically related to them.

According to the researchers, from England’s University of Cambridge and the British Antarctic Survey, the seals do this to resolve a problem known as the ‘lek paradox’.

A lek is a place where the individuals of a species gather to perform mating displays. The lek paradox states that if passive females only choose the flashiest males, only offspring with similar genetic traits would emerge. The species would eventually suffer from inbreeding, and this is something that spells doom; poor genetic diversity means vulnerability to disease and parasites.

The team studied a colony of the seals (Arctocephalus gazella) on one of the islands on Britain's South Atlantic possession, South Georgia. They tagged and took tissue samples from hundreds of adult seals and checked their DNA against the genetic ‘ID’ of the pups that were born.

They found females would travel up to 35 metres across the crowded beach breeding grounds to select a mate that had the best chance of being genetically unrelated to themselves. Only a quarter of the females conceived from their nearest male, they found.

"Many mammalian species have mating systems that were traditionally viewed as being dominated by males fighting with each other for the right to mate with passive females," said co-author Joe Hoffman. "So it's not only remarkable to uncover active female choice in such a system, but this also suggests that female choice may be more widespread in nature than we previously thought."

The female fur seals' active approach may even have saved the species from being wiped out, explained Hoffman, when the seals were nearly hunted to extinction in the 17th and 18th century by commercial sealers. By spreading their genetic diversity, the few seals remaining were able to widen the gene pool from which the species could reproduce. Their numbers are now estimated at between two and three million.

Still unclear, though, is how female seals are able to spot a partner whose genes are different from their own. The team thinks that they may use visual cues from the male's body size and condition, his dominant behaviour or the quality of the territory he occupies. Another possibility is that females distinguish closely and distantly related males by their scent.