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Ancient DNA Analysis Suggests Rapid Warming, Human Activity Drove Large Species to Extinction

NEW YORK (GenomeWeb) – Researchers led by the University of Adelaide and the University of New South Wales in Australia have compared ancient DNA and radiocarbon data with climate records to find that the extinctions of many large animal species during the last glacial period — about 110,000 to 11,500 years ago — coincided with periods of rapid warming, suggesting that fast climate change played a major part in the events.

In a paper published online in Science today, the researchers reported that "unexpectedly, rapid climate changes associated with interstadial warming events are strongly associated with the regional replacement/extinction of major genetic clades or species of megafauna."

Humans, they said, most likely had a synergistic role "in exacerbating the impacts of climate change and extinction in the terminal events."

Many so-called megafaunal species — terrestrial animals weighing more than 45 kilograms, or 100 pounds, such as the mammoth, woolly rhino, giant deer, and giant ground sloth — went extinct during the last glacial period, which happened during the Late Pleistocene, but there has been debate about the reasons why.

While some argue that humans hunted these species to extinction or changed their habitat profoundly, so they could not survive, others have pointed to climate changes as a major factor.

For their study, the researchers, led by Alan Cooper of the Australian Centre for Ancient DNA at the University of Adelaide and Chris Turney from the Climate Change Research Centre at the University of New South Wales, overlaid available time series data for a variety of species. They examined a total of 31 extinctions or invasions during a period covering about 56,000 years, with climate records derived from Greenland ice cores and the Venezuelan Cariaco Basin.

The animal records consisted of genetic, radiocarbon, and morphological data. The genetic data came from ancient mitochondrial DNA loci, in particular the hypervariable segments of the control region, which they said are commonly used for population genetic analyses.

To their surprise, they found that the species transitions — either extinctions or invasions into new habitats — were clustered around series of interstadials, or warmer periods, in particular between 32,000 to 37,000 years ago and between 14,000 and 11,000 years ago. Using statistical methods, they showed a "clear non-random relationship" between interstadial events and megafaunal transitions.

On the contrary, they found no extinctions during a major cold period, or stadial, called the Last Glacial Maximum, about 23,000 to 19,000 years ago, even though this period had previously been assumed to have driven extinctions. While the range of many species decreased during that time, "it appears that in general, cold conditions were not an important driver for extinctions even in the presence of anatomically modern humans in Europe," they wrote.

The beginning and end of interstadials were characterized by abrupt temperature shifts and changes in precipitation — making environments either wetter or drier — which likely promoted changes in the ranges and distributions of species and were "potentially sufficient to disrupt populations of taxa across a wide range of [ecological] niches," they wrote, though the outcome seems to have differed for individual species.

"Our results lend strong empirical support to the hypothesis that environmental changes associated with rapid climatic shifts were important factors in the extinction of many megafaunal lineages," the authors wrote.

Humans, they said, "could have had a major and negative impact" on those species, for example by interrupting contact between sub-populations and preventing them from migrating to resource-rich areas. Thus, they probably increased the effect of regional extinctions that were initially brought on by climate changes.

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