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 ...

Chinook salmon invade southern South America

“…At a smaller scale, the influence of lakes on water temperature at rearing sites may accelerate development facilitating an ocean-type life history ). Interestingly, most ChS from the putative source population in North America are ocean-type (Waples et al 2004) consistent with high plasticity of age at sea entrance affected by growth rate, photoperiod, or other factors (see Quinn et al 2001;Waples et al 2004, and references cited therein).…”

“…The former ranching operation was the only possible source of colonists establishing in Yelcho and Palena River basins in the 1980s. These fish were, in turn, apparently derived from the lower Columbia River basin, the former from the Cowlitz River and the latter from the Kalama River (Donaldson and Joyner 1983;Anonymous 1989) which are phylogenetically related (Waples et al 2004). There is a correspondence between the reproductive timing of ChS in South America and the reproductive timing of the putative source population in Cowlitz River (spring run with fall spawning).…”

“…It may also be that suitable niches for salmonids are widely available outside their natural boundaries (e.g., in the southern hemisphere), and thus salmonids show a high degree of success once moved by humans. Also, many species show high phenotypic plasticity and the capacity for rapid genetic adaptive evolution to new environments (e.g., Adkison 1995; Hendry et al 2000;Quinn et al 2001;Waples et al 2004).…”

“…After 3-6 years and when nearing maturity, the semelparous adults return to their natal river for reproduction although some 'stray' into neighbouring rivers (Unwin and Quinn 1993). Their life histories vary greatly both within river basins and across the range of the species (Waples et al 2004;Augerot 2005) reflecting their capacity for local genetic adaptation, made possible in part by their high site fidelity (Quinn 2005). The juveniles of some populations migrate to the ocean in their year of birth (ocean-type), while others migrate after spending typically 1 year in their freshwater stream (streamtype; Healey 1991).…”

“…It is difficult to reject the possibility that the company also used gametes from Curaco de Vélez. Nevertheless, the Curaco de Vélez' and the University of Washington's stock are closely related phylogenetically (Waples et al 2004) as both populations are derived from the lower Columbia River watershed, USA (Donaldson and Joyner 1983;Anonymous 1989). This was the last stocking for ocean ranching in Chile.…”