Ancient genomes suggest that woolly rhinos became extinct due to climate change, not to be outdone

The extinction of prehistoric megafauna such as the woolly mammoth, hollow lion, and woolly rhinoceros at the end of the last ice age has often been attributed to the spread of early humans around the world. Although overhunting led to the death of some species, a study appeared on August 13 in the journal Current biology found that the extinction of the woolly rhinoceros could have another cause: climate change. By tracing ancient DNA from 14 of these megaherbivores, researchers found that the woolly rhinoceros population remained stable and diverse until only a few thousand years before it disappeared from Siberia, when temperatures were probably too high for the cold-adapted species.

“It was first thought that humans appeared fourteen or fifteen thousand years ago in northeastern Siberia, round when the woolly rhinoceros became extinct. But recently there have been several discoveries of much older places for human occupation, the most famous of which ran thirty thousand years old, “says senior author Love Dalén, a professor of evolutionary genetics at the Center for Palaeogenetics, a joint venture between Stockholm University and the Swedish Museum of Natural History. “That the decline after the extinction of the woolly rhinoceros does not coincide so much with the first appearance of people in the region. If anything, we actually see something resembling an increase in the population during this period.”

To learn about the size and stability of the woolly rhinoceros population in Siberia, the researchers studied the DNA from tissue, bone and hair samples from 14 people. “We sequenced a complete nuclear genome to look back in time and assess population ranges, and we also sequenced fourteen mitochondrial genomes to estimate the female effective population size,” says co-first author Edana Lord, a Ph.D. .D. student at the Center for Palaeogenetics.

By looking at the heterozygosity, as well as genetic diversity, of these genomes, the researchers were able to estimate the woolly rhino populations tens of thousands of years before their extinction. “We examined changes in population size and estimated population,” says co-lead author Nicolas Dussex, a postdoctoral researcher at the Center for Palaeogenetics. “We found that after the increase in population size at the beginning of a cold period about 29,000 years ago, the woolly rhino population size remained constant and that at this point the introduction was low.”

This stability lasted until well after humans began living in Siberia, contrasting the declines expected when the woolly rhinos became extinct due to hunting. “That’s the interesting thing,” Lord says. “We don’t really see a decline in the population force after 29,000 years ago. The data we looked at only goes up to 18,500 years ago, which is about 4,500 years before their extinction, so that means they sometimes came down in that gap. “

The DNA data also revealed genetic mutations that helped the woolly rhinoceros adapt to colder weather. One of these mutations, a type of receptor in the skin to sensate hot and cold temperatures, has also been found in woolly mammoths. Adjustments such as these suggest that the woolly rhinoceros, which was particularly suitable for the harsh northeastern Siberian climate, may decrease due to the heat of a short warming period, known as the Bølling-Allerød Institute, which coincided with its extinction at the end of the last ice age.

“We get away from the idea that people take over everything once they get into an environment, and instead illuminate the role of climate in megafaunal extinction,” Lord says. “While we cannot rule out human involvement, we suggest that the extinction of the woolly rhinoceros was more likely related to climate.”

The researchers hope to study the DNA of extra-woolly rhinoceroses that lived in that crucial 4,500-year-old gap between the last genome they sequenced and their extinction. “What we want to do now is to try to get more genomic sequences of rhinos that are between eighteen and fourteen thousand years old, because they should definitely decrease at some point,” says Dalén. The researchers are also looking at other cold-adapted megafauna to see what further effects the warming, unstable climate had. “We know the climate has changed a lot, but the question is: how much have different animals been affected, and what do they have in common?”