Life-History Divergence in Chinook Salmon: Historic Contingency and Parallel Evolution

Abstract

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 ...

Genetic restoration of a stocked brown trout Salmo trutta population using microsatellite DNA analysis of historical and contemporary samples

“…However, even in the case of significant gene flow between these two populations we cannot entirely rule out local adaptations. For instance, in Chinook salmon Oncorhunchus tshawytscha, Waples et al (2004) found significant run-time differences among populations exhibiting F ST values as low as 2%. This option should therefore only be chosen after careful consideration.…”

Rapid parallel evolution of standing variation in a single, complex, genomic region is associated with life history in steelhead/rainbow trout

“…In addition, when the same traits respond to similar selective pressures in multiple species or populations, parallel evolution may lead to similar phenotypic changes [9][10][11]. In such cases, these parallel phenotypic changes may have the same underlying genetic basis [12 -17] or may involve different genetic changes that cause similar phenotypic responses [18,19].…”

Stock‐Specific Size and Timing at Ocean Entry of Columbia River Juvenile Chinook Salmon and Steelhead: Implications for Early Ocean Growth

“…These two ageclasses are associated with specific life history types (Healey 1983(Healey , 1991. In the Columbia River basin, spring runs of Chinook Salmon typically have yearling smolts, fall runs have subyearling smolts, and summer runs can have subyearling or yearling smolts (Waples et al 2004; the terms "spring," "summer," and "fall" refer to the season in which adults return to freshwater). However, hatchery practices have allowed the production of smolts outside the typical smolt age (e.g., fall Chinook Salmon released as yearlings).…”

“…The Columbia River basin is ideal for this because its ecologically diverse subbasins support numerous populations of Chinook Salmon O. tshawytscha and steelhead O. mykiss (hereafter referred to collectively as "salmon") that are genetically and phenotypically distinct yet that all enter the ocean at a common location (Rich 1920;Busby et al 1996;Waples et al 2004). Although a variety of factors likely influence migration timing (Whalen et al 1999;Beckman et al 2000;Achord et al 2007;Sykes et al 2009), our fundamental hypothesis was that ocean entry timing would largely be a function of distance to the ocean, i.e., that stocks lower in the basin (closer to the ocean) would enter the ocean earlier than those farther upstream.…”