Mittwoch, 5. November 2008

Hyperdisease extinction

The extinction (and extinction of species in general) of the mammoths, and a large amount of different species of the Pleistocene megafauna, is one of the most puzzling paleomysteries. Climate change, human overkill and last, but not least, a meteor were blamed to have wiped out the large mammals at the end of the ice age.
New studies now propose (or sustain) an ulterior hypothesis, a hyperdisease to explain the extinction of two endemic rat species.
In 1899 the cargo vessel "S.S. Hindustan" landed on the small Christmas island (island between Australia and Indonesia), and with the ship the black rat (Rattus rattus), and his fleas, came on land. The fleas infected the endemic species of rats (the Bulldog Rat Rattus nativitatis and Maclari`s Rat -Rattus macleari) with a new parasite, Trypanosoma lewisi. In 1908 the two species were declared extinct.
Researchers of the Norfolk University (Virginia) now have provided the evidence that a high infection (at least one third) rate between the native population caused a high mortality, and in the end the extinction of the two species. It’s the first time that research connects an extinction event between mammals with a particular disease or pathogen. In general it was assumed that a infection can not cause complete extinction, because normally a growing resistivety to the pathogen develops in the population, or the diminishing number of individuals prevents further spread of the disease.
The study maybe give new support to a controversial hypothesis to explain the Pleistocene extinction event.
A disease (in this case tuberculosis, spread by the first humans) was argued by some researchers to have caused the extinction of the Mammoth.

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