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But this concept also points to more extreme policy options. "I'm not going to be that person," said Mills, "but a person could start talking about 'directed evolution.' Should we be taking hares from Colorado that turned white two weeks later and moving them up to Montana because they will be able to change their phenotype"their physical appearance"in a way that tracks climate change? That very quickly becomes a discussion of, should we be playing God to try to direct evolution? It's an extremeand possiblepolicy discussion."
Scientists have begun using the term "evolutionary rescue" to describe situations in which species can save themselves from oblivion by adapting to altered environments. In a study published in the journal Science last summer, Andrew Gonzalez and Graham Bell, biologists at Montreal's McGill University, set out to learn whether baker's yeast could evolve to live in saltier conditions. They found that over a relatively short period of time, the yeast evolved ways to deal with a major change to its environment. (The yeast's success in a saltier world depended on whether its population was connected to other populations, enabling genes to migrate, and how quickly salinity increased. Populations that experienced a slow rise in salinity, and had time to build up useful genetic mutations, were far better able to survive a sudden salt increase later.)
You can't exactly extrapolate from single-celled fungi to mammalsas Gonzalez put it, "There's no way we can use yeast to predict how the polar bear will fare"but it's a step toward understanding how evolution and ecology interact.
"If a species experiences lots of variability in temperature throughout the year, you'd predict it has a high tolerance to changes in temperature," said Chris Funk, a biologist at Colorado State University who is researching that hypothesis in insects. Bugs that live in the world's temperate mountains, such as the Rockies, could fare better than their counterparts in tropical mountainsin Ecuador, for examplebecause they've already evolved to tolerate greater fluctuations.
"The question right now," said Funk's colleague Amy Angert, a CSU biologist who studies plants, "is, do people need to be aiding dispersal," that is, moving plants and animals? "Or will species be able to change quickly enough, through evolutionary adaptation, in a way that will help offset that need? They don't need to rely solely on movement if they can run in place."'
Keeping up with weather
In his race to understand the hidden biology of the snowshoe hare, Mills is leaving no lodgepole log unturned. His collaborators include Paulo Alves, a Portuguese scientist who helped sequence the rabbit genome; Steve Running, the climate scientist, who is creating highly localized models that can predict the amount of snow for any day of the year at any specific spot in Mills' study area; and Jeff Good, a geneticist who recently joined the faculty at Missoula.
In the basement of a building not far from Mills' office, dozens of Siberian hamsters scurry about in plastic cages. The cute little dwarf hamsters, roughly the size of gerbils, are native to southern Russia and Kazakhstan. Like snowshoe hares, they change from dark to light and back again with the seasons. Good is breeding them, exposing them to various amounts of light, and studying things like their metabolic rate and how much heat they can retainall in an effort to decipher the genes and genetic pathways involved in seasonal coat-color change.
Crucial to unlocking the mystery of the morphing fur is one fairly basic question: Are hares genetically programmed to change at a certain pace?
One potential clue may lie in the Pacific Northwest. There, some groups of snowshoe hares stay brown all year. "Just about every coat-color-changing species you can name has some part of their range where they don't change," said Mills. This indicates genetic variationa version of a gene or group of genes that makes coats change color, and another version that keeps them the same year-round. It may be possible, then, for populations of hares to evolve different coat-color reactions.
"If they have potential to evolve," said Mills, "you've gotta think about facilitating the process of evolution." That means ensuring that there are lots of hares in each population, that they can mingle with hares from other populations and that they aren't stressed by such things as diseases or clear-cuts.
The presence of genetic variation also gives researchers convenient tools to study the mechanisms of color change. With his Siberian hamsters, Good is hoping to find a gene that might control the transformation's onset. They could then look for a version of that gene in hares. If hares in Montana and Washington had different forms of the gene, it could prove that the color shift is genetic.
Even in places where most hares change color, some individuals remain brown all year round. So Mills and his colleagues are also asking, are there differences in gene expression, or hormone production, among the hares? It's a lot of steps, a lot of research, and a lot of "ifs."
Still, as daunting and wide-ranging as Mills' project is, some preliminary answers are already emerging. Unpublished results suggest that the hare population is shifting its cycles from one year to the next to stay in sync with the weatheran environmental response, rather than an evolutionary one. Mills and Marketa Zimova, a master's student from the Czech Republic who is studying the specifics of the hares' coat changesas she put it, "How do they change, when, how long does it take, and what is the cost of mismatch"have graphed two years' worth of information on the animals' seasonal color alongside data on snow accumulation.
On the graph, a gray line indicates the snow and a black line shows the average whiteness of the Seeley Lake hares. The lines track each other. Last year was a big snow year; autumn was fairly normal, but the spring snow stuck around much longer than usual. "The amazing thing," said Mills, tracing the lines on the chart with his finger, "is that the hares shifted remarkably." They began to change back to brown at the same time they normally do, but they stayed mostly white for about two weeks longer than they did in 2009, when there was far less snow in the spring. At Mills' second field site, near Gardiner, the snow persisted even longer. And the hares stayed white even longer, too.
- photo by Colin Ruggiero
- Mills lugs an armful of traps.
Last winter, the region had the greatest number of days with snow on the ground in the past 40 years. Meanwhile, the previous winter ranks among the lowest for that period. "So in those two years, we got a window on the kind of drastic change we might expect to see over the next 80 years," Mills said. "And the result is that hares, at least to a large extent, were able to adjust the (pace of their) coat change to match the snow."
Based on other seasonal phenomena that are better understood, such as fattening up and growing thicker fur, Mills thinks temperature might control the rate of change. He's scattering temperature monitorslittle metal buttonsaround his field sites and attaching them to the hares' radio collars to determine whether the animals have some sort of thermal regulator that helps them change quickly or slowly. The buttons measure the outside temperature, and will ideally show whether hares choose to hang out in warmer or cooler places to speed or slow their change. (If a warmer temperature could help a hare stay brown longer in the fall, for example, and if the ground was still brown around him, it might seek out a nice south-facing slope.) "Maybe," said Mills, "there's not the mismatch you'd expect intuitively."
On the bleak November morning in the Seeley-Swan Valley, we scrambled down a dangerously steep slope on the trail of a female hare. We found it in a cozy hollow under a juniper bush surrounded by a sprinkling of snow. Its fur, visible when you came up close, was predominantly white, though here and there on its small bodyon its face, its neck, its enormous front feetremnants of its brown summer garb persisted. Still, it was far more white than the first hare we saw.
Studying hares in the wild is a bittersweet endeavor. Biologists who study larger, long-living mammals, such as bears, might track the same individual animal for years. With hares, though, you're never sure if each encounter will be the last. "You really kind of get attached to them," Mills said. (After he finished his Ph.D., Mills couldn't bear to part with some voles from his dissertation research; he brought them along when he moved from Santa Cruz to Moscow, Idaho, where he briefly worked before coming to Missoula.)
Seitz snapped some photos and flushed the hare from its juniper hideout so the team could see it in full view. Sultaire recorded the coat color and snow cover data, while Mills got down on all fours to inspect the hollow. An excellent home for a hare, he concluded. Only a very wilyor very hungrycoyote would venture onto a hillside this steep.
And then it was time to head back to the truck. "See you next week," Seitz called to the hare, as we climbed back up the hill. "Hopefully."
A different version of this story appeared first in High Country News.