Genetic Structure of Chum Salmon (Oncorhynchus keta) Populations in the Lower Columbia River: Are Chum Salmon in Cascade Tributaries Remnant Populations?

Abstract

The lower Columbia River drainage once supported a run of over a million chum salmon. By the late 1950s, the run had decreased to often a few hundred fish. With the exception of Grays River near the coast and an aggregation of chum salmon spawning in creeks and the main stem near Bonneville Dam in the Columbia Gorge, most populations were thought to be extinct. However, chum salmon consistently return in low numbers to tributaries originating in the Cascade Range: the Cowlitz, Lewis, and Washougal rivers. To assess whether Cascade spawners were strays or remnants of former populations, chum salmon from the Coastal, Cascade and Gorge ecoregional zones were characterized at 17 microsatellite loci. Significant heterogeneity in genotype distributions was detected between zones and collections formed regional groups in a neighbor-joining tree. Cascade collections had higher allelic richness and private alleles, and the Cowlitz River supported genetically divergent fall and summer runs, the only summer chum salmon run extant in the Columbia River drainage. We propose that chum salmon in the Cascade zone are remnants of original populations. We attribute the divergence between zonal groups to diverse ecological conditions in each zone, which promoted regional genetic adaptation, and to genetic drift experienced in small populations.

Efficiency of the inbreeding coefficientfand other estimators in detecting null alleles, as revealed by empirical data of locusoke3across 65 populations of chum salmonOncorhynchus keta

“…The practice of excluding loci, however, may be difficult to extend to large‐scale population studies because some populations may be free of null alleles at a given locus whereas other populations may have them. For example, in multiple samples of chum salmon Oncorhynchus keta (Walbaum 1792), taken from the Columbia River, U.S.A., no deviation from Hardy–Weinberg expectations at the SSR locus oke3 were observed (Small et al , ), whereas a strong deviation attributable to oke3 null alleles was observed in the Kuril Islands, Russia, O. keta (Kordicheva et al , ).…”

Non-invasive sampling reveals fine-scale genetic structure in black bear Ursus americanus populations from northeastern Mexico

“…Several studies on the genetic structure of vertebrates have provided indications of the possible effects of natural and artificial dispersal on subpopulations of a particular species (Friesen et al 2006, Small et al 2006, McDevitt et al 2013. Other studies have shown the importance of habitat fragmentation and heterogeneity and the effects of genetic drift of subpopulations as a consequence of restricted dispersal (Bergl & Vigilant 2007, Heller et al 2010.…”