GENETIC STRUCTURE OF THE WESTERN NORTH AMERICAN AQUATIC GASTROPOD GENUS TAYLORCONCHA AND DESCRIPTION OF A SECOND SPECIES

摘要

The Bliss Rapids Snail (Taylorconcha serpenticola) is a threatened species that ranges along a short reach of the middle Snake River in southern Idaho. Additional Taylorconcha populations of uncertain taxonomic status have recently been discovered in other portions of the Snake River basin (Owyhee River, lower Snake River). We investigated the phylogenetic relationships and population structure of these snails, together with two outgroups, using cytochrome c oxidase subunit I (COI) of mitochondrial DNA and the first internal transcribed spacer region between the 18S and 5.8S ribosomal DNA. These data show no sharing of haplotypes or genotypes among T. serpenticola and the Owyhee-Lower Snake populations, with both depicted as monophyletic units within the Taylorconcha clade. Both of these datasets and morphological evidence suggest that the Owyhee-Lower Snake populations are a distinct species, which we describe herein (T. insperata new species). Application of an available COI molecular clock suggests that Taylorconcha arose in the late Miocene, when ancestral Snake River drainage was impounded in an extensive lacustrine system (‘Lake Idaho’) in western Idaho. The shallow population structuring of T. insperata suggests that the lower Snake River was only recently colonized subsequent to incision of Hells Canyon, draining of Lake Idaho, and development of a through-going river in the late Neogene. The absence of significant genetic structure in T. serpenticola, which is attributed to the unstable course and flow regime of the middle Snake River during the Quaternary, suggests that this species can be treated as a single management unit.