Lahontan Cutthroat Trout (ONCORHYNCHUS CLARKII HENSHAWI): Population Genetics of an Endangered Species
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Nevada’s state fish, the Lahontan Cutthroat Trout (Onocorhynchus clarkii henshawi), is an invaluable species to both the freshwater ecosystems where it occurs and the inhabitants of the state. Since they were first discovered in 1844, the species has experienced dramatic reductions in population and range size, with many extirpation events including populations in the Tahoe, Walker, and Pyramid lakes. This subspecies is currently classified as threatened under the United States Endangered Species Act. I analyzed the population genetics of 36 river and lake populations which are now found primarily in fragmented habitats, using 18 nuclear non-coding microsatellite loci and 755 samples. Microsatellites markers allow for genetic analysis of populations with small degrees of genetic divergence, allowing for characterization of genetic variation and delineation of population genetic structure, which give clues into how current threats are affecting these fish. The analyses show that many of the small isolated populations have low levels of genetic variation, with evidence of bottleneck events and inbreeding in many cases. The lack of a meta-population dynamic, the historical population structure, is very clear, and genetic differentiation exists among extant populations. If the species is to persist, efforts must be made to restore the ability to migrate among streams and increase home range size.