Posted on 28/03/2012
A mammoth tusk sticking out of Siberian permafrost
Before becoming extinct, a small number of woolly mammoths managed to survive for several thousands of years without suffering from inbreeding, according to new research by an international research team, including academics from Royal Holloway, University of London.
Although the mammoth disappeared from mainland Eurasia and North America some 10,000 years ago, a small population managed to survive on Wrangel Island for another 6,000 years. Wrangel is a small island in the Arctic Ocean, and it has been discussed whether the island itself is so small that the mammoths inhabiting it were essentially destined to become extinct due to inbreeding and loss of genetic variation. However, an international study published in the journal Molecular Ecology, March 2012, shows that the mammoths were in good genetic health up until they finally became extinct.
Using a novel approach to analyse ancient genetic variation, and doing so on a large number of mammoth remains, the researchers were able to track temporal changes in genetic diversity in great detail.
“We discovered that about half of the genetic variation was lost at the end of the last Ice Age, some 10,000 years ago”, said lead author Dr. Veronica Nyström. “However, we found no further loss in variation during the ensuing 6,000 years when mammoths were isolated on Wrangel Island”.
This suggests that the mammoth population on Wrangel Island was large enough to maintain genetic diversity and avoid inbreeding. To investigate this further, the researchers used an advanced computational approach to estimate the population size on Wrangel Island.
“We estimated the effective population size on Wrangel Island to be around 500 individuals”, said Pontus Skoglund, a computational geneticist at Uppsala University in Sweden.
The effective population size, which is roughly equal to the number of reproducing individuals in a population, is a measure that geneticists use to examine how evolutionary processes affect populations.
“What’s really interesting is that maintaining 500 effective individuals is a very common target in conservation programs”, said senior author Dr. Love Dalén from the Swedish Museum of Natural History. “Our results therefore support the idea that such an effective population size is enough to maintain genetic diversity for thousands of years”.
“Although we used the same genetic technique as that utilised by forensic teams today, this is the first time this approach has been applied to an Ice Age population”, added Dr Ian Barnes from the School of Biological Sciences at Royal Holloway, who designed the study together with Dr. Dalén; “Permafrost is amazing at preserving DNA, and samples recovered from it constitute a fantastic window into the factors that drove past extinctions”.