Climate Change-Induced Hybridization in Flying Squirrels

While there are many studies examining the effects of human activity on biodiversity<!–[if supportFields]> XE “biodiversity” <![endif]–><!–[if supportFields]><![endif]–>, fewer examine the anthropogenic effects on the evolutionary mechanisms that govern biodiversity. This study, conducted by the research team Garroway et al. (2010) takes a closer look at one such mechanism: hybridization. For this experiment, the researchers examined the DNA of two separate species of flying squirrel, Glaucomys volans<!–[if supportFields]> XE “Glaucomys volans” <![endif]–><!–[if supportFields]><![endif]–> and Glaucomys sabrinus<!–[if supportFields]> XE “Glaucomys sabrinus” <![endif]–><!–[if supportFields]><![endif]–>. Though the two species classically reside in habitats that are close but not overlapping, a recent series of warm winters, brought on by global climate change, led G. volans to expand it’s territory 200 km north, and into that of G. sabrinus.The researchers hypothesized that this would create instances of hybridization between the two species. They found that not only were there examples of genetic hybrids between the two species but that there was also evidence of backcrossing without extensive introgression, implying that the hybridization was recent and therefore an indirect result of the recent climate change. This is likely the first report of contemporary climate change acting as a catalyst in the creation of new hybrid<!–[if supportFields]> XE “hybrid” <![endif]–><!–[if supportFields]><![endif]–> zones. —Emily Cole
Garroway, C. J., Bowman, J., Cascaden, T. J., Holloways, G. L., Mahan, C. G., Malcolm, J. R., Steele, M. A., Turner, G., Wilson, P. J., 2010. Climate change induced hybridization in flying squirrels. Global Change Biology 16, 113–121.

The researchers collected specimens through live trapping in two separate locations. The first was Ontario, Canada<!–[if supportFields]> XE “Canada” <![endif]–><!–[if supportFields]><![endif]–> where they designated 26 different sites ranging from the north shore of Lake Erie to the southern edge of the boreal<!–[if supportFields]> XE “boreal” <![endif]–><!–[if supportFields]><![endif]–> forest<!–[if supportFields]> XE “boreal forest” <![endif]–><!–[if supportFields]><![endif]–>, which encompassed the original upper bound of G. volans’s habitat prior to its 200 km northward expansion.  They collected specimens here from 2002–2004. They also conducted live trapping at 19 sites in Pennsylvania<!–[if supportFields]> XE “Pennsylvania” <![endif]–><!–[if supportFields]><![endif]–>, USA . The results from this study site showed that all remaining G. sabrinus populations in the state were coexisting with G. volans, indicating a widespread shift in habitat.
Once the squirrels were trapped, the researchers obtained their DNA through removing 20–30 hairs and suspending them in a solution at 37 °C for 12 hours. After processing the DNA the squirrel’s genotypes were analyzed and scored. Each animal was assigned a Q value, which represented the amount of that individuals genome devoted to a certain species. An individual was defined as highly assigned to a species if it’s Q value was greater than 0.95 for that species. Hybrids were defined as individuals with Q values greater than 0.20 but less than 0.80.

Using these criteria, the researchers discovered a total of 11 hybrid<!–[if supportFields]> XE “hybrid” <![endif]–><!–[if supportFields]><![endif]–> squirrels, which constituted 4% of the population sampled. They also found squirrels with Q values high enough to be assigned to one species but which also contained genetic markers for the other species. These were assumed to be the offspring of hybrids who had crossed back again with the parental species, or possibly, but less likely, with another hybrid. They were taken as evidence of hybrid fertility. As there were instances of extensive introgression the researchers concluded that the hybridization was recent and most likely an effect of the new habitat boundaries. While the researchers conceded that hybridization can be a positive result if it aids in adaptation, they also stated that it is generally considered a negative process as it results in a net loss of biodiversity<!–[if supportFields]> XE “biodiversity” <![endif]–><!–[if supportFields]><![endif]–>. This article exemplifies some of the effects that can be expected when a species copes with climate change through migration rather than adaptation. 

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