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The influence of post-glacial recolonization and contemporary stream network on the evolution of genetic diversity within species : an examination of microsatellite DNA variation in rainbow trout (Oncorhynchus mykiss) Tamkee, Patrick

Abstract

Understanding the relative influence of historical and contemporary factors shaping patterns of genetic diversity is a major challenge in population and conservation biology. Patterns of genetic diversity were examined in rainbow trout throughout British Columbia to address the roles of historical isolation, postglacial dispersal, and local contemporary geomorphic features in structuring patterns of genetic variation and differentiation observed in nature. Microsatellite DNA was useful in detecting patterns of historical isolation and post glacial recolonization, showing clines of genetic variation as populations were studied in an orderly manner moving away from the putative refugia. Patterns of isolation by distance were observed among drainages closest to each refuge and were absent among populations at the periphery of the species’ range suggesting the existence of clines in migration drift equilibrium. Clines in genetic variation and isolation by distance were not observed in coastal populations and may result from ongoing gene flow which would prevent the detection of such trends. On a broad geographic scale, rainbow trout populations were structured into major regions and further structured within each major region into smaller watersheds and drainages based on hydrological topography. The influences of elevation, number of connections between streams, fluvial distance, migration barriers and streamllake order were important in shaping observed patterns of genetic diversity among rainbow trout populations. Anadromous and fluvial populations generally displayed higher levels of genetic variation and lower levels of differentiation than lacustrine populations. Generally, within drainage, high levels of dispersal and gene flow were observed between geographically proximate and contiguous lakes. Streamllake order was a better predictor of genetic variation than lake surface area and perimeter. Although founder events and postglacial dispersal likely played large roles in determining the broad scale patterns of genetic diversity in rainbow trout, the results suggest that contemporary factors can strongly modulate historical patterns. To properly plan for the conservation of such species, it is necessary to understand the nested nature of variation exhibited by rainbow trout populations and how important stream hydrology is because it demonstrates the importance of dispersal corridors in much the same way as land formations do for terrestrial vertebrates.

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