Collaborative Research: Ecological Correlates of Introgressive Hybridization Between Native and Introduced Populations of Salmonid Fishes

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This proposal focuses on the ecological and genetic impacts of the introduction of non-native rainbow trout (Oncorhynchus mykiss) on native gene pools of threatened Yellowstone cutthroat trout (O. clarki bouvieri). In addition to competition, predation and the introduction of disease organisms by introduced species, for some native fish species, a major threat is that of hybridization with the introduced species. Hybrids, if fertile, can spread and cause the complete replacement of parental genes with those of the introduced species. This study is designed to determine the extent of hybridization between Yellowstone cutthroat trout and rainbow trout as well as the degree of genetic dilution that has occurred in native gene pools. In addition, the study will also test whether particular features of the environment (temperature, elevation, stream flow, etc.) are correlated with the presence or absence of pure species or hybrids. In this manner, the study will determine if particular environments favor the spread of hybrid fishes, or provide an advantage to the remaining pure populations of Yellowstone cutthroat trout.This study will provide the first documentation of the pattern of genetic invasion of rainbow trout and begin to explore the ecological mechanisms that are responsible for this pattern. If environmental correlates are found which predict the success of native Yellowstone cutthroat trout over hybrids, such habitats can be given top priority for conservation. Only through a combined approach of understanding both the ecological and genetic factors that influence the success of invasive species, can we ever hope to deter their spread and save native gene pools