A run of salmon facing new environmental conditions diverged into two populations in as few as 13 generations — a time span of only about 60 years — according to research conducted at the University of Washington with sockeye salmon in Lake Washington and the Cedar River near Seattle.
As adaptable as scientists have known salmon to be, this is the first time researchers have actually demonstrated how quickly salmon can evolve into two separate populations, according to Andrew Hendry, lead author of a paper in the Oct. 20 issue of Science. He was a UW graduate student when much of the work was conducted and is now a postdoctoral researcher at the University of Massachusetts. Previously the fastest-known examples of such changes have been recorded for certain insects, taking 200 to 400 generations.
In spite of the evolutionary pliability demonstrated in these latest results, scientists cannot say how or even if salmon might adapt to more dramatic or rapid changes triggered by climate change or habitats reshaped by development, according to Tom Quinn, professor with the UW’s School of Aquatic and Fishery Sciences, co-author of the Science paper and Hendry’s faculty advisor when he was at the UW. Quinn says the recent results are consistent with other research, including UW work on chinook salmon introduced to New Zealand in the early 1900s, that indicated salmon have the capacity for rapid evolution.
The Science paper is based on data collected by UW graduate students and faculty and a scientist with the Washington Department of Fish and Wildlife. The work revealed how long it took a run of sockeye salmon with common ancestry to diverge into two populations genetically different enough that they could no longer spawn with each other as successfully. When that happens the groups are becoming “reproductively isolated.” Being reproductively isolated is one of the most important benchmarks used to decide if a single species has diverged into two.
Hendry says that the differences documented are less than those typically used to delineate separate species. The key focus of this paper is that the processes leading to speciation can happen much more quickly than anyone had previously supposed, he says.
The sockeye studied were originally from Baker Lake, in northwest Washington state, and were introduced into Seattle’s Lake Washington between 1937 and 1945. Today, runs of 100,000 to 350,000 fish spawn in the Cedar River, which starts in the Cascade Range southeast of Seattle and flows into Lake Washington. Another smaller group of descendents was first documented breeding along Pleasure Point Beach on Lake Washington, south of Bellevue, in 1957.
The divergence scientists detected between these two populations came in response to conditions that favor different traits. For example, deep-bodied male sockeye — males that are wider than average from their top fin to their bellies — would be more successful mating in the waters off the beach than in the Cedar River, where deep-bodied fish are more likely to be stranded in shallow water, eaten by predators or be less maneuverable in fast water.
The reproductive isolation of the two populations was established using genetic analysis conducted by UW’s Marine Molecular Biotechnology Laboratory, which showed that fish hatched in the river but trying to spawn at the beach had little success. If the immigrants from the river had been equally successful in producing offspring, then the two populations would have been homogenous.
The work was funded mainly by the UW from a fund endowed by Seattle businessman and sports fisherman Mason Keeler. Co-authors with Hendry and Quinn are John Wenburg, a UW graduate student when this work was conducted and now a postdoctoral researcher at the University of Montana; Paul Bentzen, UW’s director of the Marine Molecular Biotechnology Laboratory; and Eric Volk, with the Washington Department of Fish and Wildlife.
Hendry, former UW graduate student, now at University of Massachusetts, 413-545-3565, firstname.lastname@example.org
Quinn, University of Washington, 206-543-9042, email@example.com
Bentzen, University of Washington, 206-685-9994, firstname.lastname@example.org
Wenburg, former UW graduate student now at University of Montana, 406-243-5503, email@example.com
Volk, Washington Department of Fish and Wildlife, 360-902-2759, firstname.lastname@example.org
Image of sockeye available: Contact Sandra Hines, (206) 543-2580, email@example.com