Until now, scientists have blamed the extinction of species such as the tundra mammoth, the 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 ADN 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 10ºC 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 Dalén, 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 cold-adapted species, a rapid shift to a warm period and a decline in bush and tundra habitat would not have been ideal for the woolly rhino. “
To know more about the size and stability of the population of these rhinos, the 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 the specimens that are currently preserved in different scientific collections in Russia, in Moscow, Yakutsk Y 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 occupation sites, the most famous being around 30,000 years old.
“The decline towards extinction of the woolly rhinoceros does not coincide with the first appearance of humans in the region. On the contrary, we see something that looks a bit like an increase in the size of the population during this period, ”says Dalén.
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 endogamia Estimated. “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 the interesting thing,” says Lord. “Actually,” he adds, “we do not see a decrease 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 against 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 in the skin to detect warm and cold temperatures, is also present in woolly mammoths.
These kinds 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 inter-seasonal period, 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 we clarify the role of climate in the 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.
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.
The end of the megafauna
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 woolly mammoth genome. As with the rhino, we do not see any decline in population size relative to the arrival of humans around 30,000 years ago. However, the mammoth survived a bit longer on the Siberian continent and did not disappear from the continent until about 11,000 years ago. We are also working on genome sequencing of other Ice Age species, such as the cave lion, musk ox, and the Dicrostonyx groenlandicus”, afirma 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 ”.