Genetic diversity and population structure of the threatened Bliss Rapids snail (Taylorconcha serpenticola)

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1. The Bliss Rapids snail is a federally listed yet poorly known small caenogastropod which lives in the Snake River drainage (main stem river and spring-fed tributaries) of south-central Idaho. The construction of three large dams along this portion of the Snake River during the 20th century is thought to have fragmented a single, ancestral population of this species into genetically isolated subunits that are vulnerable to extinction. The authors of this article assessed variation of 11 microsatellite loci within and among 29 samples (820 snails) from across the entire range of the Bliss Rapids snail to assess genetic structure and test whether habitat fragmentation resulting from dam construction has impacted population connectivity. 2. The overall FST [ST should be subscripted] (0.15133, P < 0.05) and pairwise comparisons among samples (384 ⁄406 significant) indicated extensive population subdivision in general. A consistent trend of isolation by distance trend was not detected by Mantel tests. No evidence was found of reduced genetic diversity attributable to segmentation of the Snake River, and genetic variation among portions of drainage separated by the dams was not significant. Population structuring in spring–tributary habitats was considerably greater than in the main stem river as evidenced by differences in FST [ST should be subscripted] (0.18370, 0.06492) and the number of private alleles detected (16, 4) and by the results of an assignment test (69.4%, 58.7% correctly classified to sample of origin) and Bayesian genetic clustering algorithm. 3. The results provide no evidence that dam construction has genetically impacted extant populations of the Bliss Rapids snail. The authors speculate that the generally weaker genetic structuring of riverine populations of this species is a result of passive dispersal within the water column, which may enable occasional passage through the dams. The somewhat stronger structuring observed in a portion of the river (Shoshone reach) which receives discharge from many springs may be due to local mixing of main stem and more highly differentiated tributary populations. The findings parallel recent, genetically based studies of other western North American freshwater gastropods that demonstrate complex population structure that conflicts with traditional concepts of dispersal ability and sensitivity to putative barriers.

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ELECTRONIC FILE - Zoology: Invertebrates