Large populations of woolly mammoths wandered freely across North America and Siberia 45,000 years ago. However, 10,000 years ago, due to a warming climate and human hunting, mammoth populations dwindled to small colonies scattered on Arctic islands between Russia and Alaska. There, the majestic beast finally died out 3,700 years ago.
The common theory was that woolly mammoth extinction was due to external factors such as climate change. However, biologists at the University of North Carolina at Charlotte and the University of California, Berkeley recently discovered another potential factor at play: the build-up of harmful mutations that affected the mammoth’s ability to survive in their changing environment.
The researchers came to this discovery by comparing the DNA from a 45,000 year old woolly mammoth from mainland Siberia against the DNA of a 4,300 year old woolly mammoth who lived on Wrangel Island, an Arctic island north of Siberia which was home to the final 300 mammoths.
“In [the Wrangel] Island mammoth there is an excess of what look like bad mutations right before the mammoths go extinct” states Rebekah Rogers, co-author of the study and professor of bioinformatics and genomics at the University of North Carolina at Charlotte.
The most notable mutations included changes to the woolly mammoth’s fur and urine.
Woolly mammoths use their fur to insulate themselves and stay warm in cold environments. As such it is normally thick and long. The DNA from the Wrangel Island mammoth, however, showed a mutation which, as seen in mouse models, produces a silky, shiny, and transparent fur known as satin fur.
Socially, the mutations to the Wrangel Island mammoth’s urine most likely affected their mating habits and social status. Like their elephant descendants, woolly mammoths used urinary proteins as pheromones to prompt mating behaviours and determine social status. However, the genes which encoded and produced these urinary proteins were shut down in the island mammoth’s DNA.
What’s most surprising about these mutations is the fact they could accumulate at all. According to Rogers, the small population size made natural selection ineffective because there was not enough competition.
“Under these circumstances any mammoth was better than no mammoth at all … Bad mutations that would normally be weeded out weren’t removed from the population because of reduced competition,” she explains.
Rogers and other researchers caution that the one individual mutation is not indicative of an entire species’ DNA, and that the mutations might not have directly led to the extinction of the mammoth.
However, her team’s discovery has important implications for animal conservationists.
“This study was very interesting because it let us look at a snapshot of ‘before’ and ‘after’ a change in population size within a single species” says Rogers.
“The longer an endangered species remains a very small population, the more likely it is to accumulate these bad mutations”, explains Rogers. This means simply returning a species to normal population levels might not be enough to maintain a population of healthy animals.
Rogers states: “You may want to monitor those populations even when it seems like they are healthy to make sure that bad mutations aren’t affecting them.”
Image: Mauricio Antón via Wikimedia