Scientists demonstrate mammal extinction due to disease
Wednesday, 05 Nov 2008 06:35
Diseases carried by Eurasian black rats caused the rapid extinction of Christmas Island native rats
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Scientists have claimed that diseases carried by Eurasian black rats caused the rapid extinction of Christmas Island native rats - the first study to demonstrate extinction in a mammal because of disease.
The report published in PLoS One today claims that the black rats carried a pathogen that exterminated two endemic species, Rattus macleari and Rattus nativitatis on the Indian Ocean island.
The findings support a hypothesis proposed a decade ago, that "hyperdisease conditions" – unusually rapid mortality from which a species never recovers – can lead to extinction.
"This study puts into play pathogenic organisms as mediators of extinction," said Alex Greenwood from the American Museum of Natural History.
"Our study is the first to correlate a pathogen with an extinction event in mammals, although we know about disease-associated extinction in snails and disease-associated population declines in amphibians."
Black rats were introduced to Christmas Island via the SS Hindustan in 1899. A few years later a parasitologist noted that fleas on the rats carried a pathogenic protozoan related to the same organism that causes sleeping sickness in humans.
While the black rats were well adapted to this protozoan, known as Trypanosoma lewisi, the native rats were not and by 1908 they were extinct.
"Within nine years of contact, these abundant, endemic species were evidently completely knocked out by an introduced disease - nothing else was around at the time that could have done the job," added Ross MacPhee, from the museum.
Mr Greenwood said that today's study should get people to think about the spread of pathogen pollution - the introduction of animal or plant diseases into a new environment.
"This pollution could affect many species that are in decline or in small numbers, ranging from accidental to active introduction like the building of Pleistocene Park in Russia or the repopulation of species for conservation purposes," he stated.