Taxonomy of the Speckled Dace Species Complex (Cypriniformes: Leuciscidae, Rhinichthys) in California, USA

Abstract

The Speckled Dace, Rhinichthys osculus (Girard), is a small species of fish (Cypriniformes, Leuciscidae) that has the widest geographic range of any freshwater dispersing fish in western North America. The dynamic geologic history of the region has produced many isolated watersheds with endemic fish species. However, Speckled Dace from these watersheds cannot be differentiated readily by morphometrics and meristics. This has led to the widely accepted hypothesis that the dace's adaptability and ability to cross geologic barriers has resulted in interbreeding among neighboring populations, maintaining the dace as a single species. We investigate this hypothesis by looking at Speckled Dace populations in California which are the result of at least three separate colonization events of isolated watersheds. We synthesize results from taxonomic, genetic, and zoogeographic studies in combination with the findings of a recent genomics study, to show that there are distinctive evolutionary lineages within the Speckled Dace complex. These lineages are used to designate multiple species and subspecies. We back up these designations by examining how well these lineages fit with the geologic history of the isolated basins they inhabit and with the presence of other endemic fishes. We conclude the following nine taxa can be recognized within the Speckled Dace complex in California. Santa Ana Speckled Dace, Rhinichthys gabrielino new species Desert Speckled Dace, Rhinichthys nevadensis (Gilbert) new combination Lahontan Speckled Dace, R. nevadensis robustus (Gilbert) new combination Amargosa Speckled Dace, Rhinichthys nevadensis nevadensis (Gilbert) Long Valley Speckled Dace, R. nevadensis caldera new subspecies Western Speckled Dace, Rhinichthys klamathensis (Evermann and Meek) Klamath Speckled Dace, R. klamathensis klamathensis new combination Sacramento Speckled Dace, R. klamathensis achomawi new subspecies Warner Speckled Dace, R. klamathensis goyatoka new subspecies.