Influence of Introduction History on Genetic Variation in Introduced Populations: A Case Study of Oregon Chub

Abstract

Population introductions and reintroductions have become a common tool for conserving threatened species, but oftentimes introduced populations have reduced the genetic diversity compared with the source population they were founded from. Population introductions played an important role in the recovery of the Oregon Chub Oregonichthys crameri, a small floodplain minnow found in western Oregon. Unlike many introduction efforts, introduced populations of Oregon Chub were founded using large numbers of individuals (hundreds in many cases) and each population had a unique introduction history (e.g., number of founders, source populations selected, duration of the introduction effort). We used microsatellite loci to examine 13 introduced populations and their respective sources to evaluate how well the introduction program captured genetic diversity present in the wild populations. Genetic variation was reduced by roughly 25% in one introduced population, and three introduced populations showed evidence of a genetic bottleneck due to heterozygote excess. Populations introduced from multiple sources had greater genetic diversity than populations from a single source. When multiple source populations were used, all source populations contributed genetic material to the introduced population, though the proportional contribution from each source population varied. Using correlation analyses and general linear models, we explored the relationship between introduction history variables and genetic diversity. Our top-ranked models included genetic diversity in the source population, and this variable had the highest variable importance weight (0.999), but the number of founders and the number of source populations were also important. Overall, the Oregon Chub introduction program was highly successful at capturing the genetic variation observed in natural populations. Results of this study will be useful for planning future population introductions for Oregon Chub and other species of conservation concern.

Received November 9, 2015; accepted June 18, 2016 Published online October 7, 2016

ACKNOWLEDGMENTS

Funding for this project was provided by the U.S. Fish and Wildlife Service Region 1 Fisheries Program and the Oregon Department of Fish and Wildlife. We thank the biologists and technicians who helped collect genetic samples used in this project, Lara Amata, Matt Diggs, and Jennifer Whalen for providing laboratory assistance, Doug Peterson for assistance with data analysis and interpretation, and Christian Smith, Patty Crandell, Shaun Clements, and Mike Meeuwig, as well as two anonymous reviewers for providing comments on earlier versions of this manuscript. Any mention of specific product names does not constitute endorsement by the U.S. Fish and Wildlife Service. The findings and conclusions in this manuscript are those of the authors and do not necessarily reflect the views of the U.S. Fish and Wildlife Service. Genotypic data generated for this study have been archived online in the Dryad data repository DOI: 10.5061/dryad.4nb25.