When the parasitic skin disease mange broke out on a small Russian island, more than 90% of the local Arctic fox population died. Now, about forty years later, researchers demonstrate the visible consequences of this “population bottleneck” on the Arctic foxes’ morphology.
By Miguel Prôa and Olga Nanova
In the late 1970s, a mange epidemic on Mednyi Island – one of Russia’s Commander Islands in the North Pacific Ocean – led to a mass mortality in Arctic foxes (Vulpes lagopus). In a short time, the local population dropped from about 1,000 individuals to less than ninety. This dramatic decrease resulted in what geneticists call a population bottleneck.
A recent paper, published in Mammalia, shows that the population bottleneck was so severe that it changed the morphology of Arctic foxes living on the isolated island. In the corresponding study, Russian and Portuguese researchers measured arctic fox skulls from a collection housed in the Zoological Museum of M.V. Lomonosov Moscow State University, Russia. They discovered that the skulls of Arctic foxes living on Mednyi Island before the 1970s were morphologically different from modern ones.
“We started asking ourselves: could that be because of the epidemic?” says Olga Nanova, one of the authors of the paper. She elaborates: “Morphological changes are often related to adaptation, which is the evolution of a trait over a long time period to perform a particular function.” Skull differences between Arctic foxes on Mednyi Island and individuals on the nearby, also isolated, Bering Island had been interpreted as an adaptation to hunting different types of prey, meaning that the two populations were evolving differently. However, according to the researchers, the observed changes in skull morphology within a single population happened too quickly to be explained by the slow process of adaptation.
Using a range of statistical methods originally devised by geneticists, the researchers were able to link the change in skull morphology to the loss of genetic variability due to high mortality during the epidemic. “Evolutionary studies tend to use molecular data, but it was impossible for us to collect good DNA samples from the historical collections in the museum”, first author Miguel Prôa explains. “So, luckily, we found a set of methods that allowed us to use the skull measurements instead.”
Genetic studies had already shown that the current population displayed low variability and increased inbreeding, probably because of the bottleneck effect. The mange epidemic affected arctic foxes on the Bering Island as well, but in different ways. They display smaller changes in skull morphology that cannot be immediately linked to the bottleneck.
As the researchers indicate in their paper, future conservation programmes might benefit from this new knowledge about the demographic history of the endangered Mednyi Island Arctic fox and the effects of disease on the evolution of isolated populations.
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