September 26, 2020

Prehistoric woolly rhinos became extinct due to climate change, not hunting


Until now, scientists have blamed the extinction of species such as tundra mammoth, he cave lion or the woolly rhino to overhunting. A new study, published in the journal Current Biology, reveals that the disappearance of the latter may have had a different cause: the heating.

When sequencing DNA old fourteen of these megaherbivoresThe researchers found that the population remained stable and diverse until just a few thousand years before it disappeared from Siberia, when temperatures likely rose too high for these cold-adapted species to survive. It was during the period called the Bølling – Allerød warming, 14,700 to 12,900 years ago, an event that ushered in the end of the last Ice Age.

“Some estimates say that the temperature increased by 10 ° C in a couple of centuries, which is a fairly rapid change and probably had a marked effect on both precipitation (snow cover in winter and humidity in summer) and vegetation” , points to SINC Love dalen, co-author of the work and professor of evolutionary genetics at the Center for Paleogenetics, a joint institution of Stockholm University and the Swedish Museum of Natural History.

Edana Lord, Doctoral student from the same center and co-author of the study, adds to SINC: “The air station was replaced by woody vegetation. As a species adapted to the cold, a rapid change towards a warm period and a decrease in the habitat of shrubs and tundras would not have been ideal for the woolly rhino ”.

To know more about the size and stability of the population of these rhinos, scientists analyzed the remains found in the northeast of Siberia, which was the last stronghold for this species, that is, the place where they survived the longest.

The researchers selected small fossil pieces for their DNA study, from specimens that are currently preserved in different scientific collections in Russia, in Moscow, Yakutsk and Magadan.

Humans were initially thought to have appeared in northeastern Siberia 14,000 to 15,000 years ago, dates that would coincide with the extinction of the woolly rhinoceros. However, recently there have been several discoveries of much older human-occupied sites, the most famous being around 30,000 years old.

“The decline towards the extinction of the woolly rhinoceros does not coincide with the first appearance of humans in the region. Quite the contrary, we see something that looks a bit like an increase in population size during this period,” he says Dalén.

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Reconstruction of your life from your genes

By examining genetic diversity, scientists were able to estimate woolly rhino populations for tens of thousands of years prior to their extinction.

“We sequenced a nuclear genome complete to look back in time and estimate population size. We also sequenced 14 mitochondrial genomes to estimate the effective size of the female population, ”says Lord.

The researchers examined changes in the size and inbreeding Dear. “We found that after an increase in population size at the beginning of a cold period about 29,000 years ago, the population size of woolly rhinos remained constant and that at that time, inbreeding was low,” says Nicolas Dussex. , postdoctoral researcher at the Center for Paleogenetics and co-author of the work.

This stability lasted long after humans began living in Siberia, in contrast to the declines that would be expected if they had become extinct due to the hunting. “That’s what’s interesting,” says Lord. “Actually,” he adds, “we don’t see a decline in population size after 29,000 years ago. The data that we analyze only goes up to 18,500 years ago, which is approximately 4,500 years before their extinction, so it implies that they decreased at some point in that gap ”.

Mutations that protected them from the cold

The DNA data also revealed genetic mutations that helped the woolly rhino adapt to a weather colder. One of these mutations, a type of receptor on the skin to detect warm and cold temperatures, is also present in woolly mammoths.

These types of adaptations suggest that the woolly rhinoceros, which became particularly acclimated to the cold of northeastern Siberia, was able to see its populations decline due to the heat of a short period of warming, known as the interstation, which coincided with its extinction towards the end of the last Ice Age.

“We are moving away from the idea that humans take over everything as soon as they enter an environment and instead clarifying the role of climate in extinctions of the megafauna. Although we cannot rule out human involvement, we suggest that the extinction of the woolly rhino was most likely climate-related, ”says Lord.

The researchers hope to study the DNA of more woolly rhinos that lived in that crucial 4,500-year gap between the last genome that they sequenced and their extinction. “What we want to do now is try to obtain more genomic sequences from rhinos that are between 18,000 and 14,000 years old, because at some point, they surely must have descended,” says Dalén.

Other megafauna species with the same end

Scientists are also examining another cold-adapted megafauna to see what additional effects warming and unstable weather had. “We know that the climate changed a lot, but the question is: How much were the different animals affected and what do they have in common?”

“We have previously sequenced the genome of the woolly mammoth. As with the rhinoceros, we do not see any decrease in population size relative to the arrival of humans around 30,000 years ago. However, the mammoth survived a little longer. on the Siberian continent and did not disappear from the mainland until about 11,000 years ago. We are also working on genome sequencing of other Ice Age species, such as the cave lion, muskox, and Dicrostonyx groenlandicus “says Dalén.

Lord concludes: “We hope that future ancient genomic studies on other late Pleistocene fauna will help determine how these species were affected by climatic fluctuations past ”.

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