Hybrid 'Muttsucker' Has Genes Of Three Species

"It's a pretty inconspicuous stream," says David B. McDonald, an associate professor in the University of Wyoming's Department of Zoology and Physiology. "In fact, when you look at the creek, a lot of times you have trouble even seeing any water."

What's happening in the murky waters of the appropriately-named creek also is not readily noticeable: An introduced species of fish is threatening the existence of two native Wyoming fish species -- the flannelmouth sucker and the bluehead sucker.

In a paper that will publish this week in the Proceedings of the National Academy of Science, McDonald and four co-authors detail the potential impact that the introduced fish, the white sucker, could have on "the evolutionary biology of fishes in general, and the genetic integrity of the two native fishes in particular."

The paper is the result of seven years of research by McDonald and a team of UW professors and graduate students.

Thomas Parchman, a UW zoology and physiology postdoctoral resident associate; Michael R. Bower, a former UW graduate student who now works for the National Park Service at Death Valley National Park in California; Wayne A. Hubert, leader of the Wyoming Cooperative Fish and Wildlife Research Unit; and Frank J. Rahel, a UW zoology and physiology professor, are the paper's co-authors.

"It took a lot of detective work by a lot of people," McDonald says. "And what we found was really an intriguing pattern of genetics."

By hybridizing with both the flannelmouth sucker, named for its unusual, puffy lips, and the bluehead sucker, named for the color of its head, the white sucker has created a reticulate evolution in which a species has three ancestors rather than one parent species and two descendant species. McDonald and his colleagues have tabbed the cross between the three species as a "muttsucker."

In addition, the white sucker helped facilitate introgression between the two native species, which had previously been isolated by reproductive barriers.

It's unknown how the white sucker, native to the eastern United States, found its way west. Now, McDonald says, the species is "pretty widespread" in the Colorado River region.

"We have interesting fish, like the flannelmouth and bluehead suckers -- not many people see them, admittedly -- but we have these really interesting and different fish in the rivers of the west and this white sucker could come in and turn everything into one kind of a mutt fish," McDonald explains. "There are now quite a few of these hybrid fish out there that actually have genes from all three species."

To build the basis on their paper, McDonald and his colleagues scoured Muddy Creek to collect DNA samples from the fish, amplified the DNA markers in the laboratory and then cross-checked between the three species.

Bower, who now studies one of America's rarest creatures, the Devil's Hole pupfish -- the entire population lives in a 10-foot by 70-foot thermal pool in Death Valley -- spearheaded the research project while schooling at UW, McDonald says.

The UW paper will first publish on PNAS' Early Edition (http://www.pnas.org/content/early/recent).