Hardy Chipmunks Weathered Ice Age, DNA Study Finds

Chipmunks are hardier than we thought, say scientists at the University of Illinois. The furry animals weathered the Ice Age 18,000 years ago in a northern refuge, rather than follow the great migration south.

Using DNA samples from 244 chipmunks in Illinois and Wisconsin, researchers constructed a family tree, showing that chipmunks migrated farther south only after glaciers receded.

The study, published this week in the Proceedings of the National Academy of Sciences, challenges the scientific dogma that the cold would have forced such small mammals south.

How they managed to stay alive, though, is not clear.

Kevin Rowe, the study’s lead author, said chipmunks might have survived the cold because they were really tough, or their northern refuge might not have been as frigid as previously thought, despite its proximity to a half-mile-thick ice sheet.

Rowe determined the chipmunks’ migration routes by analyzing mutations in their genes.

The longer a group of animals remains in one place, the more mutations they accumulate, increasing their genetic diversity. When a few animals leave the refuge for a new area, they take only a small number of the changes, so the new group has less variety in its genes, he said.

Chipmunk populations in northern Illinois and Wisconsin had the largest genetic diversity, indicating they had been there the longest, while groups farther south had fewer mutations, showing that they had arrived more recently.