Historical and contemporary forces shape genetic variation in the Olympic mudminnow (Novumbra hubbsi), an endemic fish from Washington State, USA

Genetic data have become increasingly useful for conservation planning when data regarding population status and long-term viability is limited. The Olympic mudminnow is the only fish species endemic to Washington State, USA. The species is an increasing priority for conservation given its limited distribution and increasing habitat loss. Presently, information important for developing conservation plans including population abundance data, knowledge of population boundaries, and estimates of gene flow among populations are limited. We used microsatellite markers to assess the level of genetic variation within and among Olympic mudminnow collections from 23 sites across the species range. Genetic variation within collections ranged widely and was greatest within the Chehalis River Basin, a former glacial refugium. Analysis of population boundaries showed that each collection site represented a unique population with the exception of collections made within two large wetland and stream complexes. Genetic variation among populations appears to be strongly influenced by glacial history and the species' life history. Populations originating from the Chehalis River glacial refugium clustered together in multiple analyses and populations from the Olympic Coast, which persisted in separate refugia and have limited capacity for dispersal, showed a high level of differentiation. Competing theories existed regarding the origins of disjunct populations in east Puget Sound and genetic data showed that these populations represent undocumented introductions rather than a glacial remnant or historic colonization from the Chehalis refugium. Data presented in this study will help fill important information gaps and advance conservation planning for this species.