The Puzzle Of Gender-Bending Salmon

University of Idaho zoologist James Nagler is sampling more chinook salmon from Northwest rivers this fall in hope of solving a puzzling mystery: are some female chinook really gender bending males? New samples indicate the mystery pervades the Columbia Basin. Nagler first genetically tested chinook in 1999. In the Columbia River’s Hanford Reach near Richland, Wash., more than 80 percent of wild-spawning females carried a genetic marker apparently unique to the male’s Y chromosome.

In samples gathered last fall, Nagler found the same male-linked genetic marker in female chinook spawning in the Yakima River and the Columbia below Bonneville Dam, more than 200 river miles downstream from Hanford. In question is the long-term health of the Hanford’s fall chinook, one of the region’s healthiest remaining runs of wild salmon.

Nagler’s research on apparent sex reversal in chinook led to an invitation to lecture at Tulane University in New Orleans in mid-October. He joined a global gathering of scientists reviewing environmental factors that could disrupt human and animal health.

Another puzzle emerged from samples gathered last fall. In the 1999 samples, female chinook from the Priest Rapids Hatchery showed no signs of the male genetic marker. In 2000, they did.

The 1999 samples seemed to implicate Columbia River water as somehow responsible. Rapid temperature changes or environmental contaminants appeared to be possible suspects. Radiation was ruled out because it most often causes sterility, not sex changes.

Then, the second round of samples from hatchery females showed they also carried the male genetic marker. “We frankly do not have a good explanation for what might be happening,” Nagler said.

The 2000 results show the need for close collaboration among the region’s salmon biologists, Nagler said. Talks under way now may lead to a gathering next year to discuss the issues.

A flurry of interest greeted a scientific report published last December that announced the 1999 test results. Nagler, Washington State University zoologist Gary Thorgaard and Pacific Northwest National Laboratory researcher Dennis Dauble published the results in Environmental Health Perspectives.

Females normally carry two X chromosomes. Nagler’s samples suggested some Columbia females were XY and could spawn super males, those with two Y chromosomes that could father only males, threatening the salmon run’s future. Sex reversal among Pacific salmon can be accomplished in the laboratory but is otherwise unknown in the wild.

The latter makes Nagler still cautious in pronouncing that Columbia chinook have swapped sexes. One explanation is that the males were transformed into females early in their development. Another explanation is the genetic marker is not unique to males in the Columbia.

Tests done on salmon that spawn elsewhere along the West Coast, however, so far have failed to find females carrying the male genetic marker, Nagler said.

He is confident his test results are accurate, Nagler said. An independent laboratory analyzed the samples and found the same results after a blind test.

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