Estimating Species Distributions of Sphaeriid Clams in the Western United States: Implications for Conservation

Abstract

Species distributions are structured by dispersal potential and responses to vicariance events. Populations of less-vagile species can become spatially isolated in insularised habitats leading to allopatric speciation. In heavily fragmented aquatic systems, such species often contribute to high rates of endemism. Sphaeriid clams are a globally distributed, yet vastly understudied, group of bivalves. They occupy nearly every type of freshwater system, including many isolated water bodies. Studies on sphaeriid diversity in North America suggest many of the species are cosmopolitan. An exception is the Sangre de Cristo peaclam, Pisidium sanguinichristi, considered endemic to a single lake in New Mexico, USA. However, the taxonomic validity of the species is debated, incurring significant conservation implications as the species of conservation concern at the state and federal levels. We examined sphaeriid genetic diversity in New Mexico and Texas to characterise endemicity and test the identity of P. sanguinichristi. Sequences of the mitochondrial 16S gene and the nuclear 28S gene were compared amongst localities and with sequences deposited in GenBank. Our results support previous inferences that much of the sphaeriid diversity across this region comprises a few cosmopolitan species, with some exception. Furthermore, we did not find evidence to support P. sanguinichristi as a unique species and therefore not a valid taxon. This study implies that sphaeriid clams do not follow the common paradigm of high endemism in isolated water bodies shown by many small aquatic species, rather they present a mixed case. The widespread species of sphaeriids in this region are not of high-conservation priority in contrast to many aquatic invertebrates found throughout arid western North America.