Chipmunks' genetics offer window on ice age
Genetic evidence gathered by University of Illinois researchers shows that chipmunks didn't all head south for the winter, so to speak, during the last ice age in the Midwest.
Chipmunks in Danville and Vermilion County show signs of having ancestors from multiple locations, probably warmer areas south and east of the glaciers – and what likely were pockets of northern and western forest amid the glaciation.
The research is evidence of a decades-old theory that the glaciers didn't turn all of the region to ice and frozen tundra.
"People have been asking these questions, it's not like we're just coming out of nowhere," University of Illinois researcher Kevin Rowe said recently. "But we're providing some of the first and strongest evidence."
"It provides a whole new window into history," said Edward Heske, director of the Illinois Natural History Survey's Center for Wildlife Ecology and a co-author of the study.
Moreover, the research offers a cautionary tale for those trying to predict the potential impact of climate change today – global warming instead of an ice age.
The results are a cogent example of how the responses of biological organisms to a changing climate can be complex, said Heske and Rowe, a UI doctoral student in animal biology and researcher with the Natural History Survey.
"This just shows you can't make naive assumptions about how things respond to climate change," Heske said. "Nature throws you a curve ball."
In addition, Heske, who also teaches at the UI, said the results can help researchers better understand how more modern changes in the landscape, such as agricultural and urban development, affect wildlife.
"We have to know what the background was that produced the existing genetic structure," he said.
The human factor, in fact, is what the researchers started out looking at, specifically the impact of urban development along rivers in the state as indicated by the genetic patterns of chipmunks and mice, Heske said.
But they found a surprising genetic mix among chipmunks around Illinois. That's an indication, among other things, that the animals didn't all stem from the same ancestors, those that migrated in from the south as the ice, which had covered the Champaign-Urbana area in 3,200 feet of the cold stuff, receded after the last ice age 18,000 to 20,000 years ago.
"They (the researchers' results) were all saying the chipmunks of Illinois didn't come here in this kind of gradual northern drift," Heske said.
Rowe and colleagues expanded their testing to include Wisconsin, Indiana and southern Michigan. Over three years, they live-trapped chipmunks in the four states, took a small DNA sample from the tips of their ears and released them.
The chipmunk's mitochondrial DNA, which can be used to trace genetic lineage, was then analyzed at the UI with an eye toward uncovering evolutionary relationships.
The mitochondrial DNA analysis provides more information than the kind of DNA fingerprinting, for example, in criminal cases. It indicates not only genetic relationships, but how strong those relationships are, Rowe said.
Rowe's analysis indicated that the majority of chipmunks from Wisconsin and in much of Illinois were closely related, probably through ancestors that survived for thousands of years in small isolated pockets of northern and western forest thought to have persisted during the ice age.
Meanwhile, the more genetically divergent chipmunks found in Michigan, Indiana and in eastern and southern Illinois likely came from multiple populations in the warmer south and east, which in the classic pattern migrated into the region when the ice moved out, the researchers conclude.
The study, part of Rowe's doctoral work, was reported this month in the Proceedings of the National Academy of Sciences.
In addition to Rowe and Heske, Ken Paige, head of the UI Animal Biology Department, and Patrick Brown, formerly with the Illinois Natural History Survey and now at Michigan State, were the study's other authors.
The American Museum of Natural History, American Society of Mammalogists and National Science Foundation funded the project.
You can reach Greg Kline at (217) 351-5215 or via e-mail at email@example.com.