Restricted gene flow between resident Oncorhynchus mykiss and an admixed population of anadromous steelhead

Abstract

The species Oncorhynchus mykiss is characterized by a complex life history that presents a significant challenge for population monitoring and conservation management. Many factors contribute to genetic variation in O. mykiss populations, including sympatry among migratory phenotypes, habitat heterogeneity, hatchery introgression, and immigration (stray) rates. The relative influences of these and other factors are contingent on characteristics of the local environment. The Rock Creek subbasin in the middle Columbia River has no history of hatchery supplementation and no dams or artificial barriers. Limited intervention and minimal management have led to a dearth of information regarding the genetic distinctiveness of the extant O. mykiss population in Rock Creek and its tributaries. We used 192 SNP markers and collections sampled over a 5‐year period to evaluate the temporal and spatial genetic structures of O. mykiss between upper and lower watersheds of the Rock Creek subbasin. We investigated potential limits to gene flow within the lower watershed where the stream is fragmented by seasonally dry stretches of streambed, and between upper and lower watershed regions. We found minor genetic differentiation within the lower watershed occupied by anadromous steelhead (FST = 0.004), and evidence that immigrant influences were prevalent and ubiquitous. Populations in the upper watershed above partial natural barriers were highly distinct (FST = 0.093) and minimally impacted by apparent introgression. Genetic structure between watersheds paralleled differences in local demographics (e.g., variation in size), migratory restrictions, and habitat discontinuity. The evidence of restricted gene flow between putative remnant resident populations in the upper watershed and the admixed anadromous population in the lower watershed has implications for local steelhead productivity and regional conservation.

The effects of diadromy and its loss on genomic divergence: The case of amphidromous Galaxias maculatus populations

“…Most studies focusing on the migratory versus resident life history dichotomy have been conducted with Northern Hemisphere species including Atlantic salmon (Salmo salar; Perrier, Bourret, Kent, & Bernatchez, 2013), brown trout (Salmo trutta; Hindar, Jonsson, Ryman, & Ståhl, 1991;Meier et al, 2014), steelhead (Oncorhynchus mykiss; Matala, Allen, Narum, & Harvey, 2017;Thrower, Hard, & Joyce, 2004) and stickleback (Gasterosteus aculeatus; Drevecky, Falco, & Aguirre, 2013;Ferchaud & Hansen, 2016;Ravinet et al, 2015). Most of these model species are economically important and are classified as anadromous, a type of diadromy characterized by the return of mature or maturing individuals to their natal streams for reproduction.…”

Dispersal and gene flow in anadromous salmonids: a systematic review

“…For example, the high values of within basin immigration rates reported for high distances all come from large river system in the US, i.e. the Fraser river and the Columbia river (Hess et al, 2014; Bett et al, 2017; Matala et al, 2017).…”