Climate change challenges deer mice migration

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Capital News Service
LANSING — Thousands of years ago, deer mice crossed the Great Lakes into Michigan’s freshly glacier-free landscape.

Credit: Center for Disease Control

It was a surprising feat that scientists discovered by analyzing DNA, but it’s one unlikely to be repeated as a warming climate pushes the mice and other mammals northward — to be trapped at the tip of Michigan’s mitten.
Those deer mice won’t be able to pull the same trick as their ancestors by moving to new habitats with a more suitable climate.
The problem: The Great Lakes are much wider than when the earlier mice made their move.
That big barrier to mouse migration could also influence the flow of genes — and the helpful traits that come with them, said biologist Zac Taylor of Thomas More College in Kentucky.
“What you end up with is this trapped group of mice on the Lower Peninsula that’s not able to either physically move north through migrations or exchange genes with populations that are farther north,” Taylor said.
The research is indicates how global warming could shrink the gene pool of certain animals, with adverse consequences for their long-term survival, he said
“Normally we think of it as neutral to bad,” he said. “Natural selection starts to break down so you can start to lose beneficial traits and properties.”
The question of what happens when migrating animals bump into the Great Lakes came up after a 2009 study of trapping records and museum specimens showed that deer mice and other species throughout Michigan have been moving north.
The best explanation for the shift is climate change, Taylor said.
“It changes the length of the winter and the he severity of the winter,” he said. “As that’s happened, there have been a lot of changes going on in the small mammal community.”
To find out what kind of barrier the Great Lakes will pose to migrating species, researchers looked at how animals dealt with such obstacles in the past.
That led to DNA testing of deer mice in Michigan, Wisconsin and Ontario to see how closely groups from different areas are related. The findings gave scientists an idea of the routes the mice took to get to where they are now.
The researchers tested DNA of mice trapped in Delta, Alger, Schoolcraft, Mackinac,
Chippewa, Cheboygan, Charlevoix, Leelanau, Gogebic and Menominee counties.
Taylor said that he expected the mice to have taken simple routes around the Great Lakes, looking something like this:

  • a group from the south moved north into the Lower Peninsula,
  • a group from the west moved into the Upper Peninsula through Wisconsin,
  • a group east of Lake Superior moved west through Ontario in the direction of Sault Ste. Marie, the city where the province borders the Upper Peninsula.

Those paths are simple because they’re well-traveled and don’t require lake crossings.
A 2006 study showed that garter snakes, frogs and other kinds of mice followed the same routes when they arrived in the Great Lakes region.
Deer mice DNA tests tell a different story, however: They took a wetter route.
Most of the region’s deer mice — including those on the Lower Peninsula — likely came through Ontario near Sault Ste. Marie, Taylor said. From there, they headed west into most of the Upper Peninsula and south into the Lower Peninsula.
“It looks like from some of the finer genetic patterns that they actually managed to cross the lakes at different points and settle all those different areas,” he said.
Scientists can only guess how the mice made it across the lakes, but one explanation lies in how the land has changed over the past several thousand years.
The lakes forded by those pioneering deer mice weren’t the same big, forbidding barriers facing mice today. About 10,000 years ago, they were only half a mile wide in some places, but four miles of water now separate the Upper and Lower peninsulas.
Not only do the mice have more water to cross, they have less time to do it, Taylor said.
“Temperatures are changing really quickly and the mice are rearranging where they’re found in this region,” he said. “They don’t have 10,000 years to get from one place to another.”
(Jeff Gillies writes for Great Lakes Echo.)
© 2010, Capital News Service, Michigan State University School of Journalism. Not to be reproduced without permission.

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