Genetic divergence of sympatric resident and anadromous forms of Oncorhynchus mykiss in the Walla Walla River, U.S.A.

Abstract

Genetic structure (six microsatellites) and gene flow were examined among anadromous (steelhead; n = 326), resident (rainbow trout; n = 52), and mixed (n = 407)Oncorhynchus mykiss life‐history forms collected from the major drainages the mainstem Walla Walla River and the Touchet River within the Walla Walla River sub‐basin, Washington, U.S.A. Genetic structure was detected between the two major drainages. Exact tests, FST, multi‐locus assignment tests and a neighbour‐joining dendrogram revealed genetic divergence between sympatric reference populations of adult steelhead and resident rainbow trout in the mainstem Walla Walla River, but not in the Touchet River. Tests of Hardy‐Weinberg equilibrium indicated anadromous and resident O. mykiss reference populations were in equilibrium, but many of the mixed life‐history collections were out of equilibrium. Populations out of equilibrium in the mainstem Walla Walla River appeared to be admixtures as confirmed by multi‐locus assignment tests. This is evidence of genetic divergence probably resulting from assortative mating between life‐history forms or out‐of‐basin stocking practices.

Population genetic structure revealed by a school of the freshwater migratory fish, Brycon hilarii

“…Weak differentiation has been especially detected in vagile species of great abundance, with wide distribution and no visible barriers to gene flow (Knutsen et al, 2003;Jorgensen et al, 2005). The degree and pattern of differentiation is related to the amount of gene flow between population units, and even when genetic structuring is identified, different populations present some exchange of individuals (Pettersson et al, 2001;Narum et al, 2004;Jorgensen et al, 2005), as was observed here in the spawning school.…”

“…A number of studies have demonstrated the relationship between reproductive behavior, social organization and genetic structure of fish populations, such as the importance of homing behavior in the genetic structuring of salmon populations that spawn in different sites (Stähl, 1987). Similarly, genetic distinctiveness has been found between resident and anadromous Oncorhynchus mykiss fish (Narum et al, 2004) as well as temporal differentiations in a herring species (Clupea harengus), which were attributed to sampling in different spawning waves (Jorgensen et al, 2005). Recent studies have demonstrated familiarity and kin association in fish (Ward & Hart, 2003;Fraser et al, 2005).…”

The Genetic Basis of Smoltification-Related Traits in Oncorhynchus mykiss

“…The degree of genetic differentiation between resident and anadromous populations of O. mykiss in sympatry is variable. Most studies examining genetic differentiation between sympatric life-history types of O. mykiss reveal that alternative lifehistory forms within the same freshwater system are more closely related to one another than are the same life-history types across river systems (Docker and Heath 2003;Narum et al 2004;Olsen et al 2006;McPhee et al 2007); however, there are some instances where significant reproductive isolation has been observed between sympatric O. mykiss life-history forms (Docker and Heath 2003;Narum et al 2004). In other words, resident and anadromous O. mykiss in sympatry exhibit some level of gene flow, and there is evidence for plasticity in the expression of the alternative life histories.…”

Assessing connectivity in salmonid fishes with DNA microsatellite markers

“…Transitions in habitat conditions that occur as streams flow together within stream networks (Frissell et al 1986) have been used to identify population boundaries for stream fishes (Angermeier et al 2002;Dunham et al 2002). Accordingly, many studies of trout and charr have found that genetic population structure can be defined in terms of drainage (e.g., Angers et al 1999;Heath et al 2001;Knudsen et al 2002;Spruell et al 2003;Narum et al 2004) and stream branching patterns (e.g., Spruell et al 1999;Heath et al 2001;Wenburg and Bentzen 2001;Young et al 2004;Neville et al in press). The degree of genetic isolation among populations is also commonly related to stream distance between them, indicated by significant isolation by distance (e.g., Heath et al 2001;Knutsen et al 2001;Taylor et al 2003).…”