Red squirrels are rapidly evolving in response to global warming - they are the first mammals in which such genetic changes have been seen. The discovery could bode well for other species struggling to adapt to new conditions, say researchers.
Andrew McAdam, at the University of Alberta, Canada, and colleagues monitored four generations of squirrels in the Yukon, Canada, over 10 years. They found that female squirrels now give birth on average 18 days earlier in the year than their great-grandmothers.
They then used a statistical technique to separate changes in behaviour resulting from an individual's flexibility from those resulting from genetic changes, where the frequency of certain genes increases from one generation to the next.
The technique is called quantitative genetics, and has long been used in agriculture. It attributes about 15 per cent of the observed shift in birth date to genetic factors.
"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, who researches the effects of climate change on species at Macquarie University in Australia. "But this work offers a little glimmer of hope, at least for some species."
Live long and prosper
The driving force behind the evolutionary changes is that the warmer climate means that females with a genetic propensity to give birth earlier are more likely to have offspring that prosper.
These early-borns have a head start on their younger peers. They are bigger and more independent when autumn comes and it is time to store food, says Stan Boutin, another member of the team.
The work joins a growing body of evidence that many living things are changing their abundance, distribution and behaviour in response to increasing global temperatures. Genetic changes have been shown in American mosquitoes but this is the first study that demonstrates a genetic shift in a mammal.
However 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 because of medical breakthroughs," says Boutin.
Journal reference: Proceedings of the Royal Society of London B (DOI: 10.1098/rspb.2002.2224)
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