The woolly mammoth population had declined significantly by the end of the last Ice Age about 11,000 years ago. But some of their population persisted in small islands until 4,000 years ago. Scientists who analyzed DNA of the giant beasts found that the animal’s genome underwent massive deterioration, pushing it closer to extinction. Scientists at the University of California, Berkeley published findings of their study on Thursday in PLOS Genetics.
Woolly mammoth’s DNA was ‘falling apart’
The mammoths’ genetic material was so messed up that they had lost the sense of smell, developed a weird translucent satin coat, and shunned company. The mutations were so many and so bad that the woolly mammoth was practically guaranteed to spiral down into extinction. Lead researcher Dr. Rebekah Rogers of UC Berkeley said the mammoths’ DNA was “falling apart” right before their extinction. She described it as the first case of “genetic meltdown” in a single species.
To conduct the study, researchers took the genome of a mammoth from a time period when the species was plentiful and compared it to the genetic material of a mammoth that lived when the species was nearing extinction. It gave scientists the opportunity to see what happens to the DNA when population declines. They compared the DNA of a mainland woolly mammoth that dates back to 45,000 years ago, against the DNA of a mammoth from the Wrangel Island in the Arctic Ocean that lived 4,300 years ago.
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Inbreeding in a small population makes natural selection inefficient
The woolly mammoths first appeared nearly 700,000 years ago. These herbivores lived in North America, Siberia, and Beringia, a now submerged geographic area that once connected Siberia to the Canadian Yukon. Human hunting and a warming climate drove them to extinction on the mainland nearly 11,000 years ago. But small island populations survived until 4,000 years ago.
Existing mathematical theories suggest that a decline in population leads to genome deterioration. As the rising sea levels cut off the Wrangel Island, it led to inbreeding among woolly mammoths on the tiny island, which made the process of natural selection inefficient. Dr. Rebekah Rogers said in a statement that naturally occurring mutations in larger populations are weeded out by competition. But in a small population, there is no way to prevent the harmful mutations from being passed on to descendants. These harmful changes accumulate over time.
A lesson for conservationists
Scientists found that the woolly mammoths on the Wrangel Island had accumulated many harmful mutations in their DNA, which interfered with their gene functions. The woolly mammoths on the island had lost olfactory receptors that detect the smell. They had also lost the urinary proteins that impact their mate choice and social status.
Findings of the study could help improve conservation efforts for endangered species today. Dr. Rogers said preserving a small group of isolated animals cannot stop negative effects of inbreeding and genetic meltdown. Once the numbers of a species have declined below a certain level, it may be nearly impossible to save their genetic health. Conservationists can use genetic testing to figure out whether the genetic diversity in a species is enough to revive its population.
