Discovery of introduced and cryptogenic cochliopid gastropods in the San Francisco Estuary, California

Abstract

We report the first discovery in the San Francisco Estuary (‘Estuary’) of two cochliopid gastropods, Littoridinops monroensis and Tryonia porrecta. These identifications were based on morphological criteria and supported by analysis of mitochondrial DNA (cytochrome c oxidase subunit I, COI) sequence data. We also report the first discovery of males in parthenogenetic T. porrecta. The new records represent large range extensions for both of these North American species, which were previously recorded from predominantly brackish habitats along the western Atlantic-Gulf Coast (L. monroensis) and thermal springs in the Great Basin and lower Colorado River region (T. porrecta). The COI haplotype observed in Estuary specimens of L. monroensis differed from those detected in two western Atlantic populations by only 1–3 bp, suggesting recent divergence which is not consistent with the separation of these two areas by imposing terrestrial barriers since at least the Pliocene. We suggest that L. monroensis was recently introduced to the Estuary by transoceanic shipping, adding to the large exotic biota that has invaded this highly disturbed ecosystem. The COI haplotype observed in Estuary specimens of T. porrecta is closely similar to haplotypes detected in Nevada and Utah populations and highly divergent relative to the single haplotype observed in other California populations. The implications of these findings for the status of T. porrecta in the Estuary are unclear, because the native range of this parthenogen has not been established and its scattered distribution in the West may be attributable to natural dispersal across land (on birds) and/or anthropogenic spread. Although we suggest treating T. porrecta as cryptogenic in the Estuary, a native status may be suggested by independent (subfossil) evidence that this snail was locally present prior to establishment of the area as a major centre of human population and commerce in the 1850s.