Extensive diversification of pebblesnails (Lithoglyphidae:Fluminicola) in the upper Sacramento River basin, northwestern USA

Abstract

Mitochondrial DNA sequences from the cytochrome c oxidase subunit I (COI) and cytochrome b (cytb) genes were obtained from the nine extant, previously described species of the northwestern North American freshwater gastropod genus Fluminicola (commonly known as pebblesnails) and from a large number of taxonomically undescribed populations of these animals from the upper Sacramento River basin, California and Oregon, which is composed of the Sacramento River headwaters, and the McCloud and Pit Rivers. Phylogenetic analyses of separate and combined molecular datasets yielded well-supported and largely congruent trees delineating 13 genetically divergent and morphologically distinctive upper Sacramento basin lineages, which we describe as new species. These include two groups of closely related and geographically proximal species that are further united by unique radular or shell features. Most of these novelties have narrow geographical distributions and are restricted to headspring areas, whereas several are more wide ranging and typically occupy larger, well-integrated habitats. The highly endemic fauna of upper Sacramento River pebblesnails is not a single species flock, but instead a polyphyletic assemblage spread among four separate clades. Our phylogeny, together with the application of a COI molecular clock for Fluminicola, suggests that upper Sacramento River clades originated as a result of late Neogene separation of this basin from neighbouring regions (northwestern Great Basin, Klamath River basin), which is consistent with previous biogeographical hypotheses based on the distributions of fishes. The upper Sacramento River pebblesnails evolved in association with the complex late Cenozoic history of regional landscape and drainage and diversification was also facilitated by the invasion of and adaptation to insular spring habitats. Our findings are consistent with the generally limited dispersal ability and geologically ancient (mid-Tertiary) age of this genus and imply that other portions of northwestern North America may also harbour a large number of undescribed pebblesnail species. Journal compilation © 2007 The Linnean Society of London, Zoological Journal of the Linnean Society, 2007, 149, 371—422. No claim to original US government works.