When habitats collide

1995 was a very good year to be a southern flying squirrel in Ontario. It marked the start of a series of unusually warm winters that saw the rodents creep north 240 kilometres into the range of their larger cousin, the northern flying squirrel.

The incursion wasn’t widely noticed by humans. The two species are closely-related and look much alike with their large dark eyes and furry membrane between their front and rear legs that they use to glide.

Northern flying squirrel

As climate change shifts habitats, northern flying squirrels, such as this one, are cross-breeding with southern flying squirrels, raising questions about genetic fitness. (Brock Fenton)

But some humans were watching — including wildlife geneticist Paul Wilson and population ecologist Jeff Bowman, both from Trent University ­— and they wondered if the two species were crossbreeding and having hybrid babies.

When the researchers trapped flying squirrels and analyzed the DNA in their fur, they discovered that was exactly what was happening.

The pair now believes this is the first example of hybridization following the expansion of a species’ range due to modern climate change. Testing by the Ministry of Natural Resources and Forestry suggests roughly four per cent of Ontario’s flying squirrels are now genetic hybrids.

Hybrid wildlife is not new. However, human-induced changes such as the deliberate introductions of animals, habitat fragmentation and climate change may be bringing species together more frequently and in greater numbers than ever before.

The list of cross-breeding Canadian wildlife is already long:  the golden-winged warbler in Manitoba, Ontario and Quebec; the eastern wolf in Ontario and Quebec; and a handful of polar bear/grizzly crosses known as grizzlars in the Northwest Territories. Scientists also point to bob cat/lynx hybrids in New Brunswick, known as bob-o-linx, rainbow and cutthroat trout in Alberta, and spotted/barred owls in British Columbia.

Now what?

As humans wittingly and unwittingly move species around, is the resulting cross-breeding a good or bad thing? How will hybrids affect other animals and plants in the ecosystem? And what of endangered animals —  could hybrids genetically weaken their parent populations?

These are all tricky, and as of yet, answered questions.  As Wilson and Bowman point out, some biologists worry that accepting hybrids could give people an excuse not to protect the habitat of endangered species.  These scientists also argue wildlife hybridization threatens unique lineages, with interbreeding potentially leading to the extinction of rare species.

Trent University wildlife geneticist Dave Wilson

Trent University wildlife geneticist Dave Wilson looks for genetic adaptations in hybrid flying squirrels. (Sharon Oosthoek)

Others suspect hybrids may be Mother Nature’s answer to the rapid changes humans have wrought. They say hybrids allow for a greater mix of genes within a single population of animals and act as an insurance policy of sorts. In other words, the greater an animal’s genetic diversity, the more chance there is for it to adapt to a rapidly changing environment.

This genetic adaptability is why Wilson now studies the hybrid squirrel genome for adaptive advantages, such as the northerner’s ability to withstand cold and the southerner’s ability to fight off diseases from warmer climates.

“One could look at these hybrids as a creative reshuffling of the genetic material for a changing landscape,” says Wilson. “I mean climate change isn’t going to go away … maybe these hybrids are emerging as the most adapted animal for the changing landscape and climate.”

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