One of the most iconic large mammals of the Beringian ice age was the steppe bison (Bison priscus), which populated the Yukon and much of the rest of the northern world during the Pleistocene. This era, also known as the ice ages, lasted from about 2 million to 10,000 years ago.
Ice-core records show that climatic conditions in the Far North during the ice ages weren’t uniformly cold but fluctuated rapidly and dramatically. With these rapid temperature changes, the bison, and many other megafauna, likely faced a myriad of survival challenges. Adapting genetically to the new conditions was key, but such adaptation might take many generations, while the ice-core records show that major climate changes could sometimes be quicker. In these situations a special type of genetic modification may have been crucial: epigenetics.
“Epigenetics refers to a type of inherited character that doesn’t involve an actual change to the DNA sequence,” wrote Prof. Alan Cooper in a recent email from Australia. “It involves stretches of DNA, and the genes encoded within, being silenced through chemical or packaging modifications.”
Cooper is director of the Australian Centre for Ancient DNA at the University of Adelaide. Recently, he and his team of scientists searched for clues to this epigenetic process in the forearm bone, the ulna, of a steppe bison from (where else?) the Klondike gold fields.
The bison’s genetic material was later compared with that of some contemporary cattle and even a 30-year-old mummified cow from New Zealand.
“The key thing about epigenetic change is that it can allow a change between generations,” Cooper wrote. “For example, a mother might modify genes for growth or twinning rates of her offspring because her own food supply is poor. What is unusual about epigenetic signals is that this can then be stably inherited in subsequent generations until it is reversed again.”
Scientists are, as yet, unclear about how the whole process is controlled, he admitted. “Epigenetic modification can cause a change – such as character, shape or behaviour – to occur within one generation, which is incredibly fast. Evolution normally works by standard genetic mutations followed by selection, and this takes place over generations – tens or hundreds normally,” Cooper wrote.
He and his colleagues hypothesize that epigenetic change may actually “be a primary means of adaption” to rapid environmental shifts
– and glacial temperature shifts are known to happen quickly. There’s still more proof needed to support the hypothesis, and evidence found in the muck of the Yukon’s Irish Creek may be the key.
“We need to learn more about how important epigenetic modifications are when responding to climate change. I think there’s a strong chance that many modern conservation projects will find that epigenetic factors are a hugely important factor that has been overlooked so far. It promises to explain why certain populations are more or less suited to differing environments, or resilient to change within their own.”
Cooper’s path from Adelaide to the Klondike started with a chance reading of a book on ice age mammals by U.K. scientist Tony Sutcliffe back in 1996. A photo of a mummified cave lion leg grabbed Cooper’s attention. “I knew instantly this would have DNA in it, and set out to try and find it.”
The next step on the journey was the Frick Collection of the American Museum of Natural History. There Cooper discovered “tens of thousands” of bones that legendary Arctic explorer Otto Geist had collected during the first half of the 20th century. It appeared that no DNA researchers had yet stumbled upon this collection of treasures and Cooper set to work. “Quickly, I worked out that the best material would be from the mining sites themselves.” That eureka moment led him to the work of the great Canadian pioneer of Yukon Pleistocene paleontology, Dick Harrington.
Eventually, Yukon paleontologist Grant Zazula and University of Alberta earth sciences researcher Duane Froese introduced Cooper to the miners of the Dawson area, including the Johnsons, a family of ever-supportive placer miners from whose diggings the tell-tale bison remnant came. “We owe them a huge thanks, along with all the other miners who have indulged our crazy requests,” Cooper wrote in his email.
Prof. Cooper hopes to further explore epigenetic change in large populations of Yukon animals through tens of thousands of years to generate more understanding about tantalizing, and perhaps hope-filled, evolutionary processes.
For more information on the steppe bison go to www.beringia.com/research/bison.html
For more information about the Australian Centre for Ancient DNA go to www.adelaide.edu.au/acad/
This column is co-ordinated by the Yukon Research Centre at Yukon College with major financial support from Environment Yukon and Yukon College. The articles are archived at www.taiga.net/yourYukon.