Abstract. By jointly considering patterns of genetic and life-history diversity in over 100 populations of Chinook salmon from California to British Columbia, we demonstrate the importance of two different mechanisms for lifehistory evolution. Mapping adult run timing (the life-history trait most commonly used to characterize salmon populations) onto a tree based on the genetic data shows that the same run-time phenotypes exist in many different genetic lineages. In a hierarchical gene diversity analysis, differences among major geographic and ecological provinces explained the majority (62%) of the overall G ST , whereas run-time differences explained only 10%. Collectively, these results indicate that run-timing diversity has developed independently by a process of parallel evolution in many different coastal areas. However, genetic differences between coastal populations with different run timing from the same basin are very modest (G ST Ͻ 0.02), indicating that evolutionary divergence of this trait linked to reproductive isolation has not led to parallel speciation, probably because of ongoing gene flow. A strikingly different pattern is seen in the interior Columbia River Basin, where run timing and other correlated life-history traits map cleanly onto two divergent genetic lineages (G ST ϳ 0.15), indicating that some patterns of life-history diversity have a much older origin. Indeed, genetic data indicate that in the interior Columbia Basin, the two divergent lineages behave essentially as separate biological species, showing little evidence of genetic contact in spite of the fact that they comigrate through large areas of the river and ocean and in some locations spawn in nearly adjacent areas.Key words. Allozymes, gene diversity analysis, life-history evolution, Pacific salmon, parallel speciation, run timing. The question of how rapidly and by what mechanisms adaptive differences arise among populations is of central interest to both evolutionary biologists and conservation biologists. Evidence is accumulating that evolution can occur at a rate high enough to be amenable to experimental observation within the lifetime of humans (Thompson 1998;Hendry and Kinnison 1999;Reznick and Ghalambor 2001). In addition, a number of recent studies have demonstrated the importance of parallel evolution, or repeated evolution of ecologically equivalent traits within a taxon (Reznick et al. 1996;Pigeon et al. 1997;Rundle et al. 2000;Johannesson 2001;Johnson 2001). Both types of studies raise questions about the importance of conserving existing life-history diversity and the likelihood that traits, once lost, will evolve once again-questions that are increasingly relevant to understanding the consequences of current rates of decline in biodiversity (Bernatchez 1995;Pimm and Raven 2000;Myers and Knoll 2001).Understanding the evolution of life-history diversity in salmon is particularly challenging, both because of the enormous complexity in life-history traits expressed by these species (Groot and Margolis 1991;Waples ...

Abstract. By jointly considering patterns of genetic and life-history diversity in over 100 populations of Chinook salmon from California to British Columbia, we demonstrate the importance of two different mechanisms for lifehistory evolution. Mapping adult run timing (the life-history trait most commonly used to characterize salmon populations) onto a tree based on the genetic data shows that the same run-time phenotypes exist in many different genetic lineages. In a hierarchical gene diversity analysis, differences among major geographic and ecological provinces explained the majority (62%) of the overall G ST , whereas run-time differences explained only 10%. Collectively, these results indicate that run-timing diversity has developed independently by a process of parallel evolution in many different coastal areas. However, genetic differences between coastal populations with different run timing from the same basin are very modest (G ST Ͻ 0.02), indicating that evolutionary divergence of this trait linked to reproductive isolation has not led to parallel speciation, probably because of ongoing gene flow. A strikingly different pattern is seen in the interior Columbia River Basin, where run timing and other correlated life-history traits map cleanly onto two divergent genetic lineages (G ST ϳ 0.15), indicating that some patterns of life-history diversity have a much older origin. Indeed, genetic data indicate that in the interior Columbia Basin, the two divergent lineages behave essentially as separate biological species, showing little evidence of genetic contact in spite of the fact that they comigrate through large areas of the river and ocean and in some locations spawn in nearly adjacent areas.Key words. Allozymes, gene diversity analysis, life-history evolution, Pacific salmon, parallel speciation, run timing. The question of how rapidly and by what mechanisms adaptive differences arise among populations is of central interest to both evolutionary biologists and conservation biologists. Evidence is accumulating that evolution can occur at a rate high enough to be amenable to experimental observation within the lifetime of humans (Thompson 1998;Hendry and Kinnison 1999;Reznick and Ghalambor 2001). In addition, a number of recent studies have demonstrated the importance of parallel evolution, or repeated evolution of ecologically equivalent traits within a taxon (Reznick et al. 1996;Pigeon et al. 1997;Rundle et al. 2000;Johannesson 2001;Johnson 2001). Both types of studies raise questions about the importance of conserving existing life-history diversity and the likelihood that traits, once lost, will evolve once again-questions that are increasingly relevant to understanding the consequences of current rates of decline in biodiversity (Bernatchez 1995;Pimm and Raven 2000;Myers and Knoll 2001).Understanding the evolution of life-history diversity in salmon is particularly challenging, both because of the enormous complexity in life-history traits expressed by these species (Groot and Margolis 1991;Waples ...

Information developed during recently completed evaluations of the status of seven species of anadromous Pacific salmonids (Oncorhynchus spp.) in the Pacific Northwest was used to characterize patterns of intraspecific diversity along three major axes: ecology, life history and biochemical genetics. Within the study area, the species' ranges, and therefore the number of distinct ecological regions inhabited differ considerably, with pink and chum salmon limited to the northern areas and chinook salmon and steelhead distributed over the widest geographic range. The species showed comparable differences in the patterns of life history and genetic diversity, with chinook and sockeye salmon and steelhead having the most major diversity groups and pink, chum and coho salmon having the least. Both life history and genetic diversity showed a strong, positive correlation with the extent of ecological diversity experienced by a species, and the correlation between the number of major genetic and life history groups within a species was even stronger (r=0·96; P<0·05). Departures from these general diversity relationships found in some species (especially sockeye and coho salmon and cutthroat trout) can be explained by different interactions with the freshwater environment and, for cutthroat trout, by the occurrence of substantial intrapopulational diversity in life history traits, a hierarchical level not considered in this study.

We used genetic mixture analyses to show that hatchery summer-run steelhead Oncorhynchus mykiss, an introduced life history in the Clackamas basin of Oregon, where only winterrun steelhead are native, contributed to the naturally produced smolts out-migrating from the basin. Hatchery-produced summer steelhead smolts were released starting in 1971, and returning adults were passed above a dam into the upper Clackamas River until 1999. In the 2 years of our study, summer steelhead adults, mostly hatchery fish, made up 60% to 82% of the natural spawners in the river. Genetic results provided evidence that interbreeding between hatchery summer and wild winter steelhead was likely minor. Hatchery summer steelhead reproductive success was relatively poor. We estimated that they produced only about one-third the number of smolts per parent that wild winter steelhead produced. However, the proportions of summer natural smolts were large (36-53% of the total naturally produced smolts in the basin) because hatchery adults predominated on the spawning grounds during our study. Very few natural-origin summer adults were observed, suggesting high mortality of the naturally produced smolts following emigration. Counts at the dam demonstrated that hatchery summer steelhead predominated on natural spawning grounds throughout the 24-year hatchery program. Our data support a conclusion that hatchery summer steelhead adults and their offspring contribute to wild winter steelhead population declines through competition for spawning and rearing habitats.

Protein genetic markers (allozymes) have been used during the last decade in a genetic stock identification (GSI) program by state and federal management agencies to monitor stocks of steelhead Oncorhynchus mykiss in the Columbia River basin. In this paper we report new data for five microsatellite and three intron loci from 32 steelhead populations in the three upriver evolutionarily significant units (ESUs) and compare the performance of allozyme, microsatellite, and intron markers for use in GSI mixture analyses. As expected, microsatellites and introns had high total heterozygosity (HT) values; but there was little difference among marker classes in the magnitude of population differentiation as estimated by Wright's fixation index (FST), which ranged from 0.041 (microsatellite loci) to 0.047 (allozyme loci) and 0.050 (intron loci). For allozyme and microsatellite loci, the relationships among populations followed the patterns of geographic proximity. In computer‐simulated mixture analyses, GSI estimates were more than 85% correct to the reporting group, the exact percentage depending on the marker data set and target group. Microsatellite loci provided the most accurate estimate (83%) in the 100% upper Columbia River ESU simulation, whereas simulation estimates for the 32‐locus allozyme baseline were 93–94% for the 100% middle Columbia River ESU and two Snake River management groups. The simulations also showed that the estimates improved substantially up to a sample size of 50 fish per population. Technical advances will concomitantly increase the number of useful microsatellite loci and the rate of laboratory throughput, making this class of molecular marker more valuable for GSI mixture analyses in the near future. In the meantime, we recommend that steelhead management in the Columbia River rely on both allozyme and microsatellite data for GSI procedures.