Animals are adapting to rapid climate change

Some species that used to turn white in the winter are now staying brown year-round.

To avoid predators, twenty-one species of mammals and birds change their coat color from brown in the summer to white in the winter. However, with winters arriving later and snow melting earlier, these winter white individuals are becoming vulnerable to being mismatched on brown snowless ground. But some populations of these species that live in less snowy places are adapted to remain brown all winter; for example, weasels in the southern US and mountain hares in Ireland. In a new studyL. Scott Mills and colleagues have mapped hotspots that could foster a rapid evolutionary response to climate.

We spoke to him about the work.

ResearchGate: What motivated your study?

Scott Mills: Although the acceleration in human-caused climate change is scientifically certain, the outcome of that climate change will depend on how humans respond to it. Of course, reducing our global C02 footprint is ultimately essential, but are there other steps that people could take now to minimize extinctions of wild animals as the climate changes? This study was motivated by my desire to know what this remarkable trait -- seasonal coat color -- could tell us about how adaptation to climate has already shaped species, and how we could use knowledge of adaptation to help foster future persistence of wild animals to climate change.

RG: What did you discover?

Mills: For the first time we describe a visually compelling trait – shared by 21 photogenic species across the northern hemisphere – that is directly shaped by climate. The trait is seasonal coat color, whereby camouflage across the seasons is maintained by a daylength-triggered molt from brown in the summer to white in the winter to match the presence of snow. Interestingly, some individuals in each of the species remain brown in the winter, an adaptation to reduced or no snow, for example in southern or coastal areas. For eight species we mapped the range-wide distribution of the winter brown and winter white morphs, as well as the regions where both brown and white winter individuals would be expected to be found together. Because areas with the most variation evolve most quickly, these “polymorphic” zones emerge as hotspots for future rapid evolutionary response to climate.

RG: How did you identify these adaptive hotspots and the animals for your study?

Mills: A lot of the work was old-school natural history sleuthing to find winter specimens with known coat color and a precise collection location. Our team pored through the old literature and visited 26 museums globally to collect 2,700 samples originating from 60 countries. Then it was a major spatial modeling effort to use those known coat color samples to describe expected winter coat color across the ranges of the eight species for which there were sufficient data. In addition to winter brown and winter white areas, our spatial modeling also indicated places where it was about equally likely to be brown or white; these are polymorphic zones. Our last step was to overlay polymorphic zones shared by multiple species. For seasonal coat color species, these would be adaptive hotspots. Here in the polymorphic zones the populations are most likely to rapidly evolve towards winter brown, and to disperse the winter brown genes out into the adjacent winter white populations.

Credit: L.S. Mills research photos by Jaco and Lindsey Barnard.

RG: How much longer would you expect the white animals to exist at all? 

Mills: Well, this is the big question. And truly, the answer must be: it depends on what people do starting now! In other words, if we do not make gains in reducing greenhouse gases, and do not take action to foster adaptation, then the prognosis will be grim for many species in the next century. But with action to reduce greenhouse gases (a long-term proposition) coupled with hard work to maintain large and connected populations that best foster rapid evolutionary change, then there’s considerable optimism for the persistence of wild species.

RG: What would you like the public to take from your study?

Mills: Evolution is not magic or omnipotent, and ultimately, we must pursue a reduction in the greenhouse gases that cause climate change. But we needn’t panic; rather, pushing for large and connected populations that hold the special sauce for rapid evolutionary change will empower nature’s adaptation engine to sustain wild animals through substantial challenges. This is something that any citizen, community leader, land manager, or politician could do in the short term to help wild animals persist in the face of climate change.

RG: What has conducting this study been like for you personally?

Mills: This project is an example of the enthusiastic power of international collaborations, with 5 countries represented on the paper. Also, about half of the authors are students or post-docs, a testament to the energy of the next generation of scientists. For me, both the findings of this paper and the process of getting there, working with this incredible team, has left me with a profound sense of optimism for the future.

Featured image courtesy of L.S. Mills research photos by Jaco and Lindsey Barnard.