Safety really is in the numbers for some of Australia's iconic animals with a new study showing small island populations of platypus are in danger of being wiped out because of a lack of genetic diversity.
The finding could help improve management of other animal populations with low genetic variation such as the koala and helps explain the decimation of the Tasmanian devils from a contagious cancer.
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The paper, published this month in the Journal of Heredity, shows platypuses on the Australian mainland and in Tasmania have high levels of genetic diversity within their populations.
However those platypuses found on King Island, north-west of Tasmania, and Kangaroo Island, south-west of Adelaide, are at high risk of being wiped out.
For the study, University of Sydney doctoral student Mette Lillie, examined the immune genes of 70 platypuses from populations in Queensland, New South Wales, Victoria, Tasmania and the two smaller islands.
She says the study shows the King Island population has no diversity in its major histocompatibility complex (MHC) gene which plays a critical role in the immune system identifying pathogens and disease.
"If you have lots of variation in the MHC gene it means the populations is better able to resist disease and pathogens," Lillie says.
She says the genetic diversity has been lost because the King island population is an endemic species that has been isolated from other populations since the last Ice Age about 14,000 years ago.
Genetic diversity would have been reduced through inbreeding and random genetic drift - evolutionary forces or events that dramatically change or influence genetic diversity from generation to generation.
She says around 20 platypuses were introduced to Kangaroo Island in the 1930s and 1940s and the lack of genetic diversity is to be expected given the small size of the original population.
Epidemic risk
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Lillie says these two platypus populations are at high risk of disease epidemics because of the lack of genetic diversity.
The research team, which is headed by Associate Professor Kathy Belov, at the Faculty of Veterinary Science, has previously shown low immune gene diversity was critical in the spread of the contagious facial cancer that has wiped out the Tasmanian devils.
Lillie says the study suggests small populations of animals need to be carefully monitored for signs of disease outbreaks as an introduced disease could have a catastrophic effect on numbers.
However she rejects options such as increasing diversity by introducing new animals into the populations.
Because it has been isolated for so long, she says the introduction of other platypuses to King island could carry the risk of introducing disease.