Pleistocene bison decline found in ancient DNA

Submitted by Carla Browning
Phone: (907) 474-7778
11/25/04

Scientists have published a study showing it was climate change, not overhunting by man, that caused a major decline in bison over much of their ice-age range, centered in Beringia. By extracting ancient DNA from over 400 fossil bison-more than half from Alaska-the researchers were able to reconstruct the population dynamics of bison in North America over the past 130,000 years, including the history of their migration, colonization and extinction.

The study is led by scientists at Oxford University’s Ancient Biomolecules Centre. The recent findings and their implications are the subject of an article in the Nov. 26 issue of the journal "Science" titled "Rise and Fall of the Beringian Steppe Bison." Paul Matheus, a paleobiologist with the Alaska Quaternary Center at the University of Alaska Fairbanks, is a co-author and provided many of the Alaska samples and radiocarbon dates.

According to the authors, ancient DNA shows that bison migrated from Asia to North America via the Bering Land Bridge around 136,000 years ago, with their population doubling about every 10,000 years. According to their findings, "The analysis depicts a large diverse population living throughout Beringia until around 37,000 years ago, when the population’s genetic diversity began to decline dramatically." This decline coincides with a warm period just before the peak of the last ice age approximately 14,000-24,000 years ago. Spruce and other woody vegetation, which are found in habitats that aren’t particularly good for bison, spread in Beringia during this warm period.

"I’m a bit surprised, though, that bison apparently continued on a steady decline after 37,000 years," Matheus said, "since there was a variety of climatic periods after that when bison should have rebounded. It may just be that our statistical analyses weren’t refined enough to detect the change in the data, or we simply have too few samples, even though it’s a phenomenally large and unprecedented sample size for such a study."

Human overhunting has been implicated in the extinction of many large mammals at the end of the Pleistocene epoch, around 10,000 years ago. Significantly, this study shows that bison populations declined dramatically in places like eastern Beringia well before humans arrived on the scene around 12,000 years ago. The authors say their results help refute human over-kill hypotheses by showing that drastic changes in Pleistocene animal populations can be tied to environmental and climatic factors, not human activities. They urge similar genetic testing of other ice age mammals to see if the pattern found in bison is repeated.

Matheus is a research scientist at the Alaska Quaternary Center and a research associate at the Institute of Arctic Biology. Both are located on the University of Alaska Fairbanks campus.

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Photo captions:

Skull of an ice age bison from northern Alaska.Ancient DNA was extracted from this and more than 400 similar fossils in a study published Nov. 26 in Science examining the prehistoric genetics of bison in North America. The international team of scientists who wrote the study included researchers from UAF and government agencies in Alaska.

UAF researcher Paul Matheus holds the skull of a prehistoric steppe bison from Beringia. In the background is an artist’s reconstruction of the steppe bison, a close relative of modern bison. The paper published Nov. 26 in Science explores the genetic relationship of modern and prehistoric bison in North America. Matheus is a co-author on the paper headed up by researchers at Oxford University.