August 25, 2021
British Columbia’s Great Bear Rainforest is home to a subspecies of black bear found nowhere else on earth; the ‘Kermode’ bear (Ursus americanus kermodei). Most of these Kermode bears have black fur, but due to a recessive genetic mutation, roughly one in 10 bears have white fur, and are known as ‘Spirit’ bears. These extremely rare bears are of great interest to scientists for many reasons, including why the ratio of white to black Kermode bears is higher than would be expected if the genetic mutations were just caused by random chance. There must be a benefit to this unusually coloured fur.
A researcher from the University of Victoria set out to better understand the evolutionary advantage of having white fur, because at first glance, it might seem that white fur would be an impediment to the Spirit bears. Their hypothesis was that the white bears may be more difficult for salmon to see while they are swimming upstream to spawn. To test this theory, a model bear was built using a barrel, and covered in different combinations of fur; no fur, black body, black feet, black body and feet, white body, white feet, white body and feet. One at a time these different forms of the model were then placed into a flowing river, and whether or not salmon avoided the models was recorded.
The study showed that salmon avoided the models with black fur at a higher rate than those with white fur. Interestingly, the data suggests that the salmon are avoiding the bears with black bodies, because they stand out against the light sky above, more than bears with white bodies which are better camouflaged against the sky. This suggests that there is an evolutionary advantage for white Kermode bears; they are better able to hunt salmon which improves their chances of being healthy, surviving and passing on these beneficial genes to their offspring. This is an excellent example of survival of the fittest in action!
Source: Hakai Magazine
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