Leadbeater's possum death fuels survival fears

Bridie Smith, Science Editor

The Age, June 26, 2014

A Leadbeater possum at Healesville Sanctuary. Photo: Justin McManus

Conservation scientists have expressed concern about the genetic health of the last population of lowland Leadbeater's possums, after a fatally diseased possum arrived at Healesville Sanctuary from the wild and died.

It's the third consecutive year that a wild animal, selected because of its apparent health and value to the captive breeding program, has died.

Listed internationally as endangered, the Leadbeater’s possum is Victoria’s faunal emblem.

There are just 40 of the lowland Leadbeater’s left, living in a small patch of forest near the hamlet of Yellingbo, near Healesville.

Melbourne University conservation geneticist Andrew Weeks analysed tissue samples from the lowland possums. The most recent results reveal a 10 per cent slide in genetic diversity over the past decade.

‘’We’ve recorded a loss and that’s quite a concern,’’ he said.

The typical level of genetic diversity in a Leadbeater's possum population is 65 per cent. The diversity level in the Yellingbo population is now 45 per cent.

Dr Weeks said as populations shrank in size, the rate of inbreeding increased and genetic abnormalities could start to show. This included shorter lifespans, fewer offspring, a greater predisposition to disease and a weakened ability to fight disease.

He said while there were 40 individuals living in the Yellingbo Nature Conservation Reserve, 50 kilometres east of Melbourne, it was unlikely that all were breeding. Therefore, the animals contributing to the gene pool was smaller than the population numbers suggested.

The female possum that was brought to Healesville Sanctuary as part of a captive breeding program in May died earlier this month. A post-mortem revealed she had cancer in her reproductive tract, inflammation of the liver and kidney disease.

General manager of life science at Healesville Sanctuary Rupert Baker said the adult male that died in 2013 also had cancer, while the adult female that died in 2012 had a rare blood parasite that vets believe has never before been seen in an Australian marsupial. The deaths have prompted concerns that the population’s gene pool is too shallow to allow for healthy, resilient genetic diversity.

Healesville Sanctuary’s threatened species biologist Dan Harley said the deaths highlighted the precarious position of the wild population - and raised the difficult question as to whether authorities should start to consider bringing the wild population into captivity.

‘’We knew the wild population wasn’t going well numerically but what this says is that it’s probably not going well in terms of its genetic health,’’ Dr Harley said.

When confronted with a similar scenario with the mountain pygmy possum, scientists opted to cross-breed the Mount Buller population with the genetically distinct Mount Hotham population. The hybrid animals were then released into the wild to boost the gene pool at each location.

However it is a last resort for scientists who, where possible, try to preserve distinct groups in the wild.

"We should really only intervene when things are dire," Dr Harley said.