Red squirrels show evolution in the making
Red squirrels are zippy little creatures, constantly darting about and chattering away, and now it is known that this rapid-fire lifestyle extends right down to the level of their genes.
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Research in the Kluane area has shown that red squirrels have already changed their genetic makeup in order to cope with climate change.
(photo: Tim Karels)
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Scientists working in the Kluane area have shown that red squirrels there have already changed their genetic makeup to cope with a warming world. Their research is the first to show that mammals have undergone evolutionary change as a result of climate change.
Evolution is typically considered to be something that proceeds at a glacially slow pace, and Dr. Stan Boutin was not looking for genetic change when he began studying squirrels about 15 years ago.
Now a professor at the University of Alberta, he did research on snowshoe hares in Kluane as a grad student. But after finishing his doctorate, he wanted to switch his focus to an animal that could be tracked from the time of its birth, and the ubiquitous squirrels seemed a likely candidate.
Along the way, Boutin and his students have had to figure out many basic facts of the squirrels' life cycle, including where they nested.
Soon enough they confirmed that they nest in trees -- not underground -- and they were able to start charting an elaborate family tree that now includes more than 4,000 individual squirrels.
Among many other things, they now know that the average number of young squirrels born per year is three, the average life span is three to four years, and the average size of a territory is about one-half hectare.
Boutin has also found that red squirrels in Kluane are breeding about 18 days earlier than they did 10 years ago. Since about three generations of squirrels have come and gone over that same decade, the change per generation amounts to roughly six days.
Some of this change can be chalked up to plasticity, meaning that individual squirrels have changed their behaviour to adapt to changes in their environment.
In the Kluane area, one of the biggest environmental changes has been an increase in temperatures, particularly during the spring season, and Boutin thinks this warming trend is driving the earlier birth dates.
The exact link between climate change and birth dates has not been proven yet, but Boutin thinks that cone crops -- the squirrel's main food source -- are the key.
Boutin and his grad students were able to tease apart the behavioral changes -- which take place in individuals -- from the genetic changes -- which occur from one generation to the next.
"This has never been done before; other researchers have stopped at plasticity," said Boutin. "Only by having long-term lineages could we get at this research."
Breeders of domestic animals such as cows and horses have long collected this sort of data, plugging it into sophisticated mathematical equations used for breeding purposes.
Boutin is one of the few researchers who has been able to collect enough precise data on a wild mammal to use this same approach, referred to as quantitative genetics.
After running the various models, statistical analysis suggested that plasticity would only advance the birth date by about four of the observed six days.
They are assuming that genetic change -- the result of natural selection -- accounts for other two or so days.
"We think that squirrels that have the propensity to breed earlier are doing better," says Boutin.
While his study is a good news story for the squirrels so far, it does not predict the future. "As we continue to turn the heat up, maybe they will not be able to keep up and will eventually go extinct.
"Also they are not a typical northern animal. We don't know what this means for animals such as polar bears that cannot evolve so fast."
While the link between genetic change and climate change has earned lots of international attention for Boutin's work, his research has shown that red squirrels are also fascinating little beasts for other reasons.
Red squirrels are fiercely territorial, and vigilantly defend their home turfs and all-important seed caches, known as "middens."
When young squirrels are kicked out of the nest they must establish their own territories and middens -- often a tough task in a forest full of squirrels.
But some females go far beyond the call of parental duty, allowing one of their offspring to take over the mother's territory, dramatically improving the youngster's chances of survival.
Even more surprisingly, some females will try to take over neighbouring cone middens even before they have young, just so that they can pass these prized seed piles on to their young.
"It's the equivalent of you putting away money for your kid's university education even before you planned on having kids. That's the equivalent of it," says Boutin.
Evidence of Super-Mom behaviour, as well as genetic change, are just two examples of the discoveries that are possible when one gets to know an animal really, really well.
Boutin still has enough unanswered questions about red squirrels to fuel research in the Kluane area for some time to come.
- Professor Stan Boutin can be contacted at sboutin@ualberta.ca.
