Rhinichthys nevadensis nevadensis Gilbert 1893

Moyle, Peter B., Buckmaster, Nicholas & Su, Yingxin, 2023, Taxonomy of the Speckled Dace Species Complex (Cypriniformes: Leuciscidae, Rhinichthys) in California, USA, Zootaxa 5249 (5), pp. 501-539 : 521-523

Rhinichthys nevadensis nevadensis Gilbert 1893 new combination,

Amargosa Speckled Dace. Table 3 .

Synonymy. See Desert Speckled Dace, Rhinichthys nevadensis , account.

Holotype. See Desert Speckled Dace, Rhinichthys nevadensis , account.

Diagnosis. The Amargosa Speckled Dace is a cryptic taxon diagnosable with genomics and distribution as the Speckled Dace found in the springs, streams, and ditches of Death Valley, Owens Valley, and the Amargosa River. Individuals are typically small (8–11cm SL) and recognizable as Speckled Dace by their thick caudal peduncle, sub-cylindrical body, small fins, small eyes, and blunt pointed snout. The sides of the body are usually covered with black blotches which merge into a black stripe, which is especially dark below the eye. Gilbert’s (1893:230) short diagnosis is: “Differing from other known species [of dace] by the large head, the short deep body, very small eye, and in the reduction of the outer ventral [fin] ray to a mere rudiment.” He also noted the presence of an incomplete lateral line, of maxillary barbels, and of a conspicuous lateral stripe. See Table 3 for meristics. However, these characters, except genomics and distribution, do not separate the three R. nevadensis subspecies from one another.

Description. The formal description of Amargosa Speckled Dace (as a species) by Gilbert (1893) is thorough ( Figure 6 ) and is included in this paper as the description of Desert Speckled Dace, R. nevadensis . Scoppettone et al. (2011) measured 1354 dace from the Amargosa River Canyon, which had a mean fork length of 51mm and a maximum FL of 92 mm FL. None of Gilbert’s characters separate the regional Speckled Dace populations from one another, demonstrating the cryptic nature of Speckled Dace taxa.

Sada et al. (1995) performed a principal component analysis on 20 morphological measurements (truss analysis) and eight meristic characters on 484 Speckled Dace (386Amargosa Speckled Dace and 98 Lahontan Speckled Dace) from 13 localities ( Table 3 ); they found that “Meristic and proportional mensural characters were all within ranges documented for Speckled Dace…Highly significant differences among all populations for all characters showed the morphology of each population to be unique ( Sada et al. 1995:352–353).” Essentially, they found evidence of local adaptation and genetic drift, but no features that could readily distinguish individual Amargosa Speckled Dace from individuals in other regional dace populations, including Lahontan and Long Valley Speckled Dace. Lahontan Speckled Dace, however, did have slightly more lateral line scales than the other two subspecies but overlap in scale counts and incomplete lateral lines in many individuals makes this character unreliable for identification ( Table 3 ).

Distribution. Gilbert (1893) reported the distribution of R. nevadensis as warm water springs in Ash Meadows, Indian Creek, and Vegas Creek, Nevada. Vegas Creek has been covered up by Las Vegas and its endemic Speckled Dace, Rhinichthys deaconi , is extinct ( Smith et al. 2017). The Amargosa Speckled Dace is endemic to springs, small streams, and rivers in the Death Valley system (which includes the Owens Valley) in California and Nevada ( Figure 3 ). In the Owens Valley, it is assumed they once were found throughout the length of the Owens River ( Snyder 1917). For more details of distribution see the Notes section of this account.

Genetics/genomics. Early genetic studies generally concluded that Speckled Dace from the Death Valley region were all one lineage but included branches variously designated as Owens, Ash Meadows, Amargosa River, and Long Valley Speckled Daces. Thus, Sada et al. (1993, 1995) used protein electrophoresis to examine relationships among dace from 13 localities in the region and from the once-interconnecting Amargosa River. They found that all populations had some statistically identifiable features and that the regional Speckled Dace populations likely diverged from Lahontan Speckled Dace after vulcanism and drying-up of interconnecting waterways isolated them in the Death/Owens Valley region. Oakey et al. (2004), using mt/DNA found that all populations of Speckled Dace in the region formed a clade. The genomic analysis of Mussmann et al. (2020) produced similar results. They recommended that the populations be treated as Distinct Population Segments within the Amargosa Speckled Dace lineage because they met three criteria: current geographic isolation, genetic differentiation, and local adaptation.

According to Mussmann et al. (2020:13) “the identities of the various lineages is intimately tied to the prehistoric lakes and rivers of the region, with diversifications occurring within modern drainages. This pattern clearly reflects a relictual biodiversity with high endemicity, with patterns driven by Plio-Pleistocene tectonics and hydrology (i.e., dispersal of Speckled Dace from Owens Valley to the Amargosa Basin during fluvial events)…”. The analysis of Su et al (2022) agrees with this statement and recognizes that the Desert Speckled Dace includes three subspecieslevel lineages (Lahontan, Amargosa, and Long Valley) with the Lahontan lineage likely being the most immediate ancestral population.

Notes: Subspecies. The Amargosa Speckled Dace is here designated as a subspecies of Desert Speckled Dace ( Rhinichthys nevadensis ), going back to Gilbert’s original description and name, based on the following lines of evidence:

Taxonomy. The Amargosa Speckled Dace has been a stable taxon since it was described, although it was mysteriously switched from being a species to a subspecies of Rhinichthys osculus in the 1940s, following the Great Basin studies of Hubbs and Miller (1948) and Miller (1946). Gilbert’s original description only encompassed dace in Ash Meadows, leaving as undescribed other dace populations in the Amargosa River, Oasis Valley, and Owens Valley. The undescribed forms have been variously lumped with Amargosa ( Moyle 1976) or Lahontan Speckled Dace ( Snyder 1917, 1918) or treated as undescribed subspecies of R. osculus ( Miller 1973) . Moyle et al. (2015) divide the Death/Owens Valley daces into Long Valley, Owens, and Amargosa populations. Su et al. (2022), however, show that the Owens Valley populations are best treated a part of the Amargosa subspecies, R. nevadensis nevadensis .

Zoogeography. During pluvial periods of the Pleistocene, the Death Valley and Lahontan regions supported many interconnected large lakes, with abundant fishes (Hubbs and Miller 1948). When the climate changed and frequent precipitation stopped, the lakes and rivers dried up or became small, disconnected remnants of what they once were. As a result, the Death Valley region became an endemism hot spot with numerous endemic plants and animals in springs and wetlands ( Sada et al. 1995). The fish that survived became restricted to relatively small areas where permanent stream flows were created by springs, which is where we find them today. For Speckled Dace, this process resulted in numerous isolated populations with little opportunity for genetic exchange in the present landscape. In Death Valley proper, including Ash Meadows, the Speckled Dace shares spring systems with four species and eight subspecies of pupfish ( Cyprinodon spp. ). In the Owens Valley, other endemic fishes are Owens Tui Chub ( Siphatales bicolor snyderi ), the undescribed Toikona Tui Chub ( Chen et al. 2007), Owens Sucker ( Catostomus fumeiventris ) and Owens Pupfish ( Cyprinodon radiosus ).

Genomics. Su et al. (2022) support Amargosa Speckled Dace as a distinct lineage within Desert Speckled Dace.

Note: Distinct Population Segments. The Federal Endangered Species Act of 1973 defines species fairly broadly for fishes and other vertebrates. The act recognizes that populations that are distinct and important segments (usually defined by genetics and distribution) of a species total population can be listed as Threatened or Endangered, even if the species is not so listed. To be recognized, Distinct Population Segments (DPSs) do not go through a formal taxonomic description process.

Thus, Mussmann et al. (2020) used genomics to determine that the populations of Desert Speckled Dace could be divided into three DPSs: Long Valley, Owens River, and Oasis Valley. “Ash Meadows and Amargosa River populations are included within the Oasis Valley DPS. In addition, they recognized that dace in Amargosa Canyon are of hybrid origin (Amargosa X Ash Meadows). We treat this fish as a population of Amargosa Speckled Dace. Our analysis agrees with Mussmann et al., (2020) that the Long Valley Speckled Dace are sufficiently different to be recognized as a subspecies. However, our analysis also recognizes Ash Meadows and Owens Valley Speckled Dace as two DPS’s within Amargosa Speckled Dace.

The Ash Meadows Speckled Dace was first described from springs and their outflows in Ash Meadows. Genetically similar fish occupy similar habitat in the Oasis Valley, Nevada. In some years, the water from both areas ultimately flows into the Amargosa River and down into Amargosa Canyon. Therefore, this DPS includes daces from Ash Meadows, Oasis Valley , and Amargosa Canyon, including Willow Creek ( Mussmann et al. 2020).

The Owens Valley Speckled Dace is found only in streams, springs and ditches of the Owens Valley, California. It was considered by La Rivers and Trelease (1962) and Moyle (1976) to be a population of Amargosa Speckled Dace ( R. osculus nevadensis ). Sada (1989) and Sada et al. (1993, 1995) showed it was genetically and morphometrically separable from populations in Ash Meadows, Amargosa River, and Long Valley. Moyle (2002) and Moyle et al. (2015) recognized it as an undescribed subspecies related to Amargosa Speckled Dace. Otherwise, synonymies are as for the species ( R. nevadensis ) and subspecies ( R. n. nevadensis , R. n. caldera).

Etymology. This subspecies, as the species Rhinichthys (Apocope) nevadensis , was described by Gilbert (1893:230) from “Ash Meadows, Amargosa Desert, on boundary between California and Nevada” hence the common and scientific names. The springs in Ash Meadows ultimately drain into the Amargosa River, which flows into Death Valley. Amargosa is derived from a Spanish word meaning bitter and refers to the unpalatability of the water. Jordan and Evermann subsequently (1896) placed the species in Agosia . The members of this genus were returned to Rhinichthys in the 1940s and the species simultaneously became a subspecies of R. osculus , both without a formal process.

Conservation Status. All populations of R. n. nevadensis are threatened with extinction to a greater or lesser degree. In 1984, the Ash Meadows population was listed as endangered under the federal Endangered Species Act of 1973. The Center for Biological Diversity (2020) has petitioned to have all Speckled Dace in the Death Valley and Owens Valley region be included under that listing, albeit with a separate listing for Long Valley Speckled Dace. The main populations of Speckled Dace in the Owens Valley are in highly modified habitats in North Fork Bishop Creek and Lower Horton, Pine, and Rock creeks, and associated ditches near Bishop (N. Buckmaster, unpublished observations). Their need for special protection is illustrated by recent disappearance of the isolated Benton Valley population of Owens Speckled Dace (N. Buckmaster unpublished observation, 2022). While captive populations are maintained by the California Department of Fish and Wildlife (CDFW), it is a tenuous situation for the long-term survival of these dace. Long Valley, Amargosa River, and Owens Valley Speckled Dace are all listed as Species of Special Concern by CDFW ( Moyle et al. 2015). The causes of endangerment of dace are documented in Moyle et al. (2015) and in Center for Biological Diversity (CBD 2020).

Figures

FIGURE 3. Current distribution of Rhinichthys in California and adjacent watersheds. The distributions are only approximate but based on occurrence in HUC 12 watersheds. The numbers refer to populations in the Owens Valley and Death Valley that are included in Amargosa Speckled Dace, R. nevadensis nevadensis and can be recognized as Distinct Population Segments (1) Owens Speckled Dace, (2) Oasis Valley Speckled Dace, (3) Ash Meadows Speckled Dace, and (4) Amargosa River Speckled Dace. Long Valley Speckled Dace are a distinct subspecies. Dace have been extirpated from the south San Francisco Bay-Santa Clara Valley region. See text for more specific distributional information. Information for this map was gleaned from Gesch et al. (2002), Patterson and Kelso (2021), Santos et al. (2013), US Census Bureau (2001), USGS (2004, 2013). Speckled Dace are typically present in a limited number of streams, springs and ditches within each mapped region. Map by Amber Manfree.

FIGURE 6. Top. Holotype, Lahontan Speckled Dace, from Rutter (1903). Middle, Long Valley Speckled Dace from Whitmore Marsh, 2014, showing life colors. Photo by Jacob Katz. Bottom: Western Speckled Dace, type specimen, from Evermann and Meek (1898).