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Low Genetic Diversity is a Killer

Killer whales are one of the most widely distributed mammals on Earth, and have lived through varied threats to their existence, from natural predators to being hunted into near extinction by humans. But they're still in danger from a genetic bottleneck that's been pursuing the species since the last ice age, leading to low genetic diversity, reports Hakai Magazine.

At the tail end of the last ice age, pods of killer whales spread out from ice-free areas near the equator to live in waters that were once uninhabitable. Ever since then, some of these populations have evolved in their own isolated pods. Recent research has demonstrated that these pods have now become blocks of stagnating genetic diversity, with some pods being more inbred than others, Hakai says. 

Today, some killer whale populations are doing better than others. The pods that started out with larger numbers of founder whales have more genetic material to draw on, and they began reproducing at a high rate early on to maintain a large population size, the article says. But the more isolated groups that are getting smaller and smaller, and have little access to new genetic material, have a bigger problem, since successive generations of inbreeding are causing harmful mutations to build up in the whales' genomes. 

Killer whale pods facing this issue will only dwindle further as their lack of genetic diversity makes them unable to handle environmental shocks like pollution, habitat loss, and the decimation of their food sources, Hakai says. And the more individual whales die, the further the gene pool shrinks, and the worse the problem will get.

"Killer whales, as a species, have been hanging on — some populations, barely — since Earth thawed out from its last glaciation," the article adds. "But in their survival is a warning. With the world warming because of anthropogenic climate change, many species are already beginning their own poleward migrations. History cautions that even if a few particularly itinerant animals can outrun warming waters, it may not be without consequences — even thousands of years down the line."