Genetic Evaluation of Population Introduction Strategies for Threatened Oregon Chub

Oregon chub are a small floodplain minnow endemic to the Willamette River system of western Oregon. Dramatic declines in abundance and distribution led to its listing as a federally endangered species in 1990. A major recovery effort for the species has focused on introducing Oregon chub into suitable habitats within their historic range. Presently 16 introduced populations of Oregon chub exist and these populations have helped expand the distribution of the species and increase abundance. Partly because of this, the species was re-classified to threatened status in 2010. The number of donor populations used, the duration of the introduction period, and the total number of founding individuals varied among the different introduced populations. In this study we used a suite of microsatellite DNA markers to estimate the level of genetic variation within introduced populations and we compared these estimates to levels of variation observed in natural populations used as donor stocks. We also examined the relationships between the different introduction strategies and levels of genetic variation in the introduced populations. The majority of the introduced populations had levels of variation that were equal to or greater than the natural donor populations. One exception was a population founded using only 50 individuals. Introduced populations with more than one donor stock had significantly greater levels of genetic variation than populations introduced from a single donor stock. We observed no significant genetic differentiation among introduced populations and their corresponding donor population(s), suggesting that introduced populations were not experiencing a high rate of genetic drift. When populations were introduced using multiple donors, introduced populations contained genetic material from all donor populations in roughly the same proportions as the proportion of individuals used for the initial founding event. Data from this study will be useful for planning future Oregon chub population introductions as well as introduction programs for other threatened and endangered species.