FOR the first time, a mammal has been shown to be evolving in response to global warming. The discovery that red squirrels are adapting to climate change could bode well for other species struggling to acclimatise.
Recent studies have suggested that climate change is forcing many animals towards the cooler climes of the poles (91av, 4 January, p 4). But scientists fear that some species will be unable to move far or fast enough and could instead be driven to extinction.
Now biologist Andrew McAdam and his colleagues at the University of Alberta in Canada have shown that some mammals may be able to evolve quickly enough to adapt. In work to appear in the Proceedings of the Royal Society of London B they studied four generations of red squirrels from the Yukon region of Canada over 10 years, and found that they now give birth on average 18 days earlier in the year than their great-grandmothers.
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The researchers then used a statistical technique to work out how much of the change is down to evolution and how much is due to individual flexibility. They calculated the normal variation in birth dates for each generation and then identified squirrels that were giving birth much earlier than average. If the parents had the same trait, it was likely to have been inherited. The technique, which is commonly used in agriculture, attributes about 15 per cent of the shift towards early birth to evolution.
“Because climate change is happening so fast, the perceived wisdom is that mammals won’t be able to undergo evolution to keep up with that,” says Lesley Hughes of Macquarie University in Sydney, who studies the effects of climate change on animals. “This work offers a little glimmer of hope, at least for some species.”
The driving force for the squirrels’ evolution is that climate change has led to a steady increase in the amount of food available in spring. So females that can give birth earlier than others are more likely to have babies that survive. These early-borns have a head start on their younger peers, making them bigger and more independent when autumn comes and it is time to store food to survive the winter, says Stan Boutin, a member of the team.
The findings add to a body of evidence that animal behaviour is changing in response to global warming. Genetic changes have been found in mosquitoes, for example. But it is unlikely that humans have started to evolve in response to climate change. “We have been able to overcome so many of the selective pressures that would normally be important,” says Boutin.
