Landscape factors affect the genetic population structure of Oncorhynchus mykiss populations in Hood Canal, Washington

Abstract

Among salmonids, local adaptation can reduce gene flow among populations, which can then lead to population sub-division. As such, it is important to understand what landscape variables affect local adaptation, especially for populations for which conservation concerns exist. By examining allele frequencies at 15 microsatellite DNA loci from anadromous (steelhead) and freshwater resident (rainbow trout) Oncorhynchus mykiss collected from 7 Hood Canal, Washington rivers, we surveyed the genetic population structure within and among populations, and examined the landscape factors that could be affecting their genetic population structure. We found that samples from within a river system were more genetically similar to each other regardless of life history type or sampling location than they were to similar types from other rivers. Rainbow trout samples had lower genetic diversity then steelhead samples. We identified two main population groups among the steelhead samples. Genetic distance among populations was most strongly influenced by the populations’ locations on one of two peninsulas, and to a lesser extent, river flow rate and hydrological characteristics. These factors influence genetic population structure and local adaptation more than geographic distance, river gradient, or mean annual river temperature.