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For some orcas, inbreeding is a whale of a problem

By Lauren Appelwick

Blog Editor

According to research published in the Journal of Heredity, endangered Southern Resident orcas are mating within their family groups. This “genetic bottleneck” means the whales could be more susceptible to diseases, early mortality or failure to produce calves.

The study’s lead author is Michael J. Ford, a scientist with the Northwest Fisheries Science Center in Seattle. “In terms of how bad it is, that depends on how long the population size stays small,” he told The Seattle Times. “Brief bottlenecks don’t necessarily have to have a long-term impact. But as a general rule, we should be concerned about small population sizes because genetic diversity is the raw material for adaptation and evolution.”

Over the course of four years, the team of researchers gathered samples of blubber and skin from stranded and dead whales. They also collected mucous from live wales, and DNA samples from floating feces spotted by scat-tracking Labradors led by Samuel K. Wasser, a biologist with the University of Washington. In analyzing the DNA from 78 calves, mothers, and potential fathers, a surprising family tree emerged. The research team found that mating was dominated by a handful of aging males, the oldest of which fathered at least five calves in a single pod. (He is known as Ruffles, recognizable by his wrinkled dorsal fin.)

Ken Balcomb, Center for Whale Research executive director, told the Times Colonist that the females seem to demand a level of social maturity. “They don’t seem to have any bias against older males and that’s a nice thing for old guys to hear,” he joked.

All told, this sort of inbreeding isn’t exactly terrible, but it won’t promise long-term genetic diversity. It appears that even though the whales will mate within their own pod, they abstain from mating with immediate family. “We aren’t really sure of the social process that results in this avoidance,” said Ford.

A newborn male orca whale from K pod swimming with his mother in the San Juan Islands.

The full article has been made available free online by the Journal of Heredity.

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