Monday, 17 October 2011

Hybrid mountain pygmies hold hope of a bright future

''I HOPE you're sitting down,'' the email sent to Marissa Parrott last week began. As the reproductive biologist at Zoos Victoria read on, she discovered why. The email contained the results of a much-anticipated paternity test on Healesville Sanctuary's precious population of mountain pygmy possums.

The results showed that the tiny alpine possums, listed as endangered in Victoria and critically endangered internationally, were capable of doing what Dr Parrott had hoped for but had never seen any evidence of - producing a litter fathered by two males.

''We're all extremely excited,'' Dr Parrott said. ''It's a huge step forward in the conservation of the species.

But there was more to come. The paternity tests conducted at Melbourne University also proved for the first time that hybrid males were fertile - providing a vital new path for boosting the species' genetic diversity.

Since 2007, the mountain pygmy possum captive breeding program at Healesville Sanctuary - the only one of its kind in Australia - has been breeding hybrid animals, with one parent from Mt Buller and the other from Mt Hotham. But because the two populations are genetically distinct - a result of being separated for 10,000 years - there was no guarantee that the hybrid offspring would be fertile.

The first hybrid litter was born in 2008. All three females produced young last year, but it was only last week that the sole male of the litter, Beau, was confirmed as a first-time father.

''This was what we were hoping for, as it shows that a genetic rescue to conserve the species is possible,'' Dr Parrott said.

With just 1500 of the animals left in the wild, scientists' main challenge is keeping the species' gene pool deep enough to maintain healthy populations.

The Mt Buller population - which now numbers fewer than 30 - is of greatest concern, and it is there that the hybrid possums will be released in 2013.

The author of the email was Andrew Weeks from Melbourne University's centre for environmental stress and adaptation research. He said the Mt Buller population had had a genetic diversity rate of 60 per cent in 1996. That has since crashed to 20 per cent.

Dr Weeks said establishing that a single litter could be fathered by multiple males would bode well for the species, as the rate of genetic diversity had the potential to increase at a faster rate. ''It means we can breed up a population that is not as related as it could be and then we can release them back into the wild a lot quicker.''

Healesville Sanctuary's 81 mountain pygmy possums are about to come out of hibernation and begin their breeding season. Dr Parrott said that even before she received the paternity results confidence was high that this would prove a bumper season, with the number of young born eclipsing the record 38 last year.

Bridie Smith

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