February 25, 2012 — andyextance

Rising temperatures in the US Yosemite National Park put alpine chipmunks that live there at greater risk of disease and in-breeding. That’s due to a shrinking gene pool that Emily Rubidge from University of California, Berkeley, and her team-mates revealed this week. They compared DNA from chipmunks living in the park today against samples from museum specimens preserved for almost a century. The results provide rare evidence about how recent climate change can alter mammals’ genes, and put them in danger of dying off.

“Reduced genetic diversity may be a threat to mammals’ long-term persistence,” Emily told Simple Climate. “You could also say genetic diversity loss is a symptom of the environmental pressure these chipmunks are under. In this case, the loss is associated with local population extinctions in lower altitude areas where they were relatively abundant in the past.”

Those extinctions came because the lowest temperatures in Yosemite National Park have warmed by 3ºC over the past century. Researchers have found that this means alpine chipmunks (Tamias alpinus) today live in higher areas of the park than they did before. The lowest sightings in 2003 were over 500 metres higher than in 1915, though the closely related lodgepole chipmunk (Tamias speciosus) stuck to the same heights as it did before.

Previously, few researchers had studied how recent climate change affects mammals on a genetic level. That’s in part because it isn’t easy to find older DNA that can be compared with modern mammals. But the Museum of Vertebrate Zoology in Berkeley stores preserved chipmunks collected in 1915 and 1916 by Joseph Grinnell and his colleagues.

That gave Emily the idea to compare them against today’s chipmunks to look at the link between current climate and genetics. “I saw a unique opportunity with the paired historical and modern samples to examine changes in genetic diversity associated with the observed range shift,” she says. “The rich historical dataset allowed me to make this comparison. Usually, we don’t have that ‘before’ data.”

Shrinking fitness

To collect DNA from 146 modern alpine and lodgepole chipmunks, Emily trapped them and clipped skin from their ears before releasing them. Though the 88 museum specimens were easier to take skin from, getting the DNA out was still a different sort of struggle. “DNA extracted from skins almost 100 years old is often low in quantity and therefore we had to be very careful about contamination issues,” she explains. “There are special protocols that have to be followed, and results must be repeated and checked several times in order to finalize results.”

True to their apparent comfort with warmer conditions, the Yosemite lodgepole chipmunks showed no significant genetic change over the past 96 years. Meanwhile, nearby alpine chipmunks’ gene pool had shrunk surprisingly quickly, they showed in a paper published in research journal Nature Climate Change on Sunday. There, Emily and her colleagues call this “clear evidence that twentieth-century climate change has affected the size and connectivity of populations of this species.” “Today the alpine chipmunk population has become fragmented into more isolated subpopulations on mountaintops,” Emily added.

Normally it takes whole species going extinct, or coming close to it, to show how warming affects biodiversity. The scientists also write that instead of waiting for this to happen, looking at genetic changes reveals a “powerful and often overlooked impact of climate change”.