Natural or Human Drivers?
Ancient Bison DNA Might Help Explain Effects of Climate Change
DNA from bison that roamed North America thousands of years ago can provide insights into protecting and preserving species amid the threat of climate change, said Dr. Beth Shapiro, during a recent Wednesday Afternoon Lecture in Lipsett Amphitheater.
“The diversity we see today is the product of lots of different expansions and contractions, local extinctions, replacements, turnovers in populations,” said Shapiro, professor in the department of ecology and evolutionary biology at the University of California, Santa Cruz. “Climate—not humans, not hunters coming in and killing things for the first time—is really the first-order driver of these events.”
There are two types of bison living in North America today: plains and woods. Plains bison are generally smaller in size and have a smaller and more rounded hump than woods bison. Plains are more common in the South, while woods are found more often in the North.
Their ancestors first crossed into North America at least 160,000 years ago from Asia. Bison quickly spread and became one of the most abundant species on the continent until the turn of the 20th century when they nearly went extinct.
Shapiro and her team use the latest experimental and computational approaches to analyze bison DNA extracted from fossil and archived remains buried in permafrost. By studying ancient DNA, she can track the evolution of species over time.
“Ancient DNA refers to the state of DNA,” she said. “It’s mostly degraded—chopped up into tiny little fragments. Those fragments contain different types of DNA damage. These typical types of DNA damage make it hard to recover and make sense of the DNA.”
The field of ancient DNA first started in 1984 when Dr. Allan Wilson’s extinct species study group at the University of California-Berkeley isolated a tiny fragment of DNA from the pelt of a quagga, an extinct zebra relative. At the time, it was surprising that DNA could remain in old tissue. The research inspired Michael Crichton’s Jurassic Park.
DNA can last a very long time, but it doesn’t last forever. DNA stays preserved longest in cold areas of the world, like Siberia or the Yukon. Caves are also a great environment for long-term DNA preservation because they are cool, temperature-controlled and dark.
Shapiro and her team collect samples in Siberia or Canada, a part of the world where the Bering Land Bridge once was. During the Pleistocene, the planet’s last Ice Age, glaciers formed and sea levels dropped. A 1,000-mile-wide bridge was exposed.
Many of the iconic animals from this period, such as mammoths, mastodon and woolly rhinoceros, lived in the area, she said. Fossils from these animals can help scientists learn how fluctuating temperatures and the introduction of people affected the animals.
“The hope was to use ancient DNA to figure out why some of these species disappeared while others survived,” Shapiro said. “Is there something from the past that could tell us why some ecosystems are more resilient in the face of harsh habitat climate change that we might be able to use and apply to make more informed decisions about how to protect and preserve species today?”
When bison first arrived from Asia, they shared grassland with horses and other megafauna, or large animals. In between Ice Ages, the climate became warmer and wetter. Plants and grasslands become more abundant, she said. This habitat allowed the bovids to range further South into present-day United States. Abundant grasslands even encouraged some of these bison to evolve into Bison latifrons, also known as the giant bison.
During the coldest part of the Ice Age, a glacier formed in present-day Canada. It created a barrier. For 10,000 years, species couldn’t cross it. As a result, bison populations in the North and South became genetically distinct from each other.
During the peak of the Ice Age, 20,000 years ago, the climate became colder and drier. Grasslands declined. Once grass disappeared, bison populations declined. Horses outcompeted bovid populations temporarily, but eventually went extinct in North America. Around this time, the mammoth also went extinct. Bison nearly went extinct, as well.
“Whatever was driving these processes was driving all these animals simultaneously,” Shapiro said.
After the Pleistocene, grassland returned and the bison population exploded. Millions of bison lived on the Great American Plains. For thousands of years, they were an important source of food, clothing, shelter and tools for Native Americans. Shapiro added archeological records that show evidence of “bison jumps,” where hunters herded bison and drove them over cliffs. Tens of thousands of buffalo would be slaughtered at the same time.
In the late 1800s, European settlers hunted bison to near extinction. Conservationists intervened and the population slowly rebounded. Today, both plains and woods bison are protected separately from each other.
A changing climate is no longer changing the genetic diversity in these populations.
“Instead, it’s us,” Shapiro concluded.