Study Shows Rapid Salmon Evolution, Adaptabilityby Barry Espenson
Columbia Basin Bulletin - October 27, 2000
A recently released study indicates that salmon have a remarkable -- and evolutionarily quick -- ability to adapt to conditions in which they find themselves.
The theory is, however, a double-edged sword, researchers warn. The news cannot be interpreted to mean that salmon can and will adapt regardless of the environmental change. But it does appear to offer researchers a tighter window than they imagined to study what happens within both wild and hatchery produced salmon populations are faced with change.
The study results published in the Oct. 20 issue of Science are focused on a run of salmon that, facing new environmental conditions diverged into two populations in as few as 13 generations -- a time span of only about 60 years.
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. Previously the fastest-known examples of such changes have been recorded for certain insects, taking 200 to 400 generations.
The research was conducted at the University of Washington with sockeye salmon in Lake Washington and the Cedar River near Seattle. Hendry was a UW graduate student when much of the work was conducted and is now a postdoctoral researcher at the University of Massachusetts.
Despite of the evolutionary pliability demonstrated in the study 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 and co-author of the Science paper.
"This doesn't mean we can trash habitat and let salmon go extinct," Hendry said, expecting that they can be replaced with similar species from hatcheries or elsewhere.
"A loss of genetic stock is a loss of that genetic stock," Hendry said. The ecological niche once filled by that lost stock can be filled by reintroduced species, but they may not have the capacity to adapt as well as the native stock.
Reintroduced stocks have the potential to adapt quickly to new environments, "but there are many, many instances where they have tried and failed," Hendry said.'' Gauging the success of such experiments remains a long-term process.
"It's not a quick thing," Hendry said, noting the 60-year time frame chronicled in the UW study.
Yet reintroduction efforts, such as those under way to replace lost stocks in several areas of the Columbia Basin, are "the best controlled examples to watch evolution in action," Hendry said.
He said he hoped the UW study "will encourage research in that particular area, which I think can be valuable." Studies can help pinpoint salmon's limits to adapt to change, potentially allowing fishery biologists to mitigate for those biological limits.
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 paper also pointed out that "female body size differs between beaches and rivers because large females dig deeper nests, thereby protecting their eggs from disturbance during flooding. Flooding is absent from beaches, and females are correspondingly smaller."
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.
Scientists involved in Columbia Basin processes intended to reverse salmon declines and ward off extinctions of 12 federally listed salmon and steelhead species found the study results intriguing. Major initiatives are under way to alter hatchery practices to avoid any negative influences non-native hatchery fish might pose to wild listed stocks. Lower Columbia treaty tribes are involved in both reintroduction efforts and supplementation -- programs aimed at shoring up depleted naturally spawning populations with the outplantings of hatchery reared fish.
"We're very interested in following up on that type of research," said Phil Roger, manager of the Columbia River Inter-Tribal Fish Commission's fisheries science department. He said CRITFC intends to advance research proposals intended to study the ability of outplanted fish to adapt to their environment. Those proposals would seek funding through innovative project and high priority project categories outlined in the Northwest Power Planning Council's Columbia Basin fish and wildlife program.
Fisheries scientist Jim Lichatowich, while admitting he had not read through the study, said he liked the approach of the Puget Sound area study as described to him. It could have considerable applicability in the Columbia Basin, he said, though the problems faced in the basin are much more intricate than those posed in the Lake Washington-Cedar River study area.
The UW study focused on fish stocks that were planted "and left alone for quite a while," said Lichatowich, a member of both the Independent Scientific Advisory Board, which advises both the NWPPC and National Marine Fisheries Service on science matters, and the Independent Multidisciplinary Science Team for Oregon's Salmon Recovery Plan.
Columbia Basin fish face problems posed by an ever-changing environment -- generally degraded habitat, considerable hydrosystem influence and the continuous introduction of hatchery fish. Researchers and managers would benefit by learning more about salmon's ability to adapt and what limits that ability, Lichatowich said.
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.
learn more on topics covered in the film
see the video
read the script
learn the songs