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Inbreeding Threatens Washington Killer Whale Population

July 24, 2011

A new National Oceanographic and Atmospheric Administration (NOAA) study has raised concerns that killer whales in the Puget Sound could be facing a loss of genetic diversity due to inbreeding.

The NOAA study, which was published online this month in the Journal of Heredity, followed the Washington-based whale species and studied their mating habits. They discovered that some of the offspring had been produced as a result of matings within the same pod or social subgroup, the researchers said in a July 21 press release.

“One implication of this inbreeding behavior is a significant reduction in the genetic diversity of what is already a perilously small population of animals, formally known as Southern Resident killer whales,” the NOAA statement added. “That population numbers only about 85 animals and was listed as endangered under the federal Endangered Species Act in 2005.”

“We were surprised that, in many cases, the father was from the same pod as the mother. Based on earlier studies, we didn’t think killer whales mated within their own pod,” lead author Dr. Michael Ford, a scientist with the NOAA’s Northwest Fisheries Science Center in Seattle, said in a statement, adding that the behavior “may be unique to the Southern Resident population, perhaps related to the population’s small size.”

In the study, the NOAA scientists reviewed 26 different genetic markers in 78 whales, determining the parentage of 15 different calves. The study found evidence that suggests that, while the whales did not mate with close relatives, they would reproduce with members of their own pod–distant relatives, as it were.

They also discovered a relatively low variance of reproductive success in the whale communities, leading them to conclude that several males–not just a handful–participated in the breeding process. That said, they found that older, larger males did appear to be responsible for a greater percentage of successful matings, suggesting that females might prefer to mate with these particular characteristics.

“That trend surprises and worries researchers who say it could significantly reduce the population’s genetic diversity, making whales more susceptible to disease and genetic disorders or mutations,” Seattle Times Environment Reporter Craig Welch wrote Thursday. “Such ‘genetic bottlenecks’ can also reduce the ability to withstand environmental upheaval, such as toxic pollution or climate change.”

“It shows that the population is fairly inbred,” University of Washington professor Sam Wasser, one of the study’s authors, told Welch. “And that may have a lot of repercussions for recovery. Inbreeding tends to exacerbate all their other problems.”

Ford told UPI that, since this whale population remains isolated from other killer whale breeds, inbreeding such as this could put them at risk for potentially harmful mutations.

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