American Fisheries Society Symposium 17:350-359, 1995 © Copyright by the American Fisheries Society 1995

Desert Aquatic Ecosystems and the Genetic and Morphological Diversity of System Speckled Dace

DONALD W. SADA Environmental Studies Program, University of Nevada-Las Vegas 2689 Highland Drive, Bishop, California 93514, USA HUGH B. BRITTEN AND PETER F. BRUSSARD Biodiversity Research Center, Department of Biology, University of Nevada Reno, Nevada 89557-0015, USA

Abstract.—The morphological and genetic diversities of fishes in North American deserts have been examined to estimate evolutionary rates, to create models of interbasin pluvial connectivity, and to justify protection of aquatic ecosystems throughout the region. Morphological and genetic studies comparing 13 populations of speckled dace Rhinichthys osculus from the Death Valley system, Lahontan basin, and lower Colorado River were conducted to quantify differences among populations. Differences in meristic and mensural characteristics among populations were highly significant, but differences in body shape were slight and best explained as representing two forms, one deep-bodied and short, the other elongate and slender. Starch gel electrophoretic assays of 23 loci showed isolated populations to be genetically unique. Fifty-nine taxa are identified as endemic to wetland and aquatic in the Death Valley system: 16 forms of fish, 1 amphibian, 22 mollusks, 7 aquatic , 3 mammals, and 10 forms of flowering plants. Genetic and morphological differentiation of isolated speckled dace populations and the diversity and number of endemic forms associated with wetlands and aquatic habitats in the Death Valley system suggest that each desert wetland community functions as an evolutionarily significant unit.

Taxonomic descriptions of relict faunas occupy- Pleistocene pluvial periods (Miller 1946; Hubbs and ing isolated aquatic habitats in the endorheic desert Miller 1948). The ecology, systematics, biogeogra- basins of western North America began with recog- phy, and status of most fish in the system nition of unique fishes during land surveys before have been actively studied (Miller 1948; Soltz and the West was settled (see Minckley and Douglas Naiman 1978; Echelle and Echelle 1993) with 1991) and attention expanded quickly to the inver- the exception of speckled dace Rhinichthys oscu- tebrate fauna (Brues 1932). This fauna is depauper- lus, which occupies the Owens and Amargosa ate compared to those in more mesic regions, but basins. many studies over the last 50 years have shown that Concern for the declining status of DVS speck- a wide diversity of endemic plants and is led dace caused us to conduct morphological, associated with regional wetlands that range in size genetic, and status studies to determine charac- from less than 0.1 ha to several thousand hectares. teristics of population variation and assist in the The small size of these habitats and the vulnerabil- design of conservation programs to protect and ity of isolated populations to degradation enhance extant populations. In this paper we and invasion of nonnative species have been factors summarize results of these genetic and morpho- in the decline of many fish populations (Minckley logical studies and examine the utility of this and Deacon 1968; Williams et al. 1989; Rinne and analysis for identifying evolutionarily significant Minckley 1991). Approximately 60% of the North units. Then we consider other endemic organisms American fish species currently listed as threatened associated with DVS aquatic habitats and wet- or endangered by the U.S. Fish and Wildlife Service lands to determine if considering communities of occupy the desert southwestern region of the these organisms provides stronger justification United States (Williams and Sada 1985; Williams for regional wetland conservation than protection et. al 1989). strategies based on either populations or single The Death Valley system (DVS) is an endorheic species. We believe that a wide diversity of en- basin in southwestern Nevada and eastern Califor- demic species associated with these habitats nia. It comprises the Owens River, , would suggest that conservation programs pro- and Mojave River basins, which were tributary to tecting endemic species could also protect desert (present day Death Valley) during aquatic and wetland ecosystems. 350 DIVERSITY OF DESERT POPULATIONS 351

I. LAHONTAN BASIN 1. Smoke Creek 2 2. Reese River 2 3. Huntington Creek 1,2 1,2 4. East Fork Walker River

II. DEATH VALLEY SYSTEM

5. Spring at Little Alkali Lake 2 14 6. Whitmore Hot Springs 7. Hot Creek' 8. Marble Creek 1.2 1,2 9. Pine/Rock Creeks 2 10. A-1 Drain near Bishop Canal south of Bishop 12. Little Lake 13. Amargosa River at Tecopa 1,2 14. Tubbs Spring Ranch' 15. Bradford Spring 1.2 16. Amargosa River at Beatty 1,2

III. LOWER COLORADO RIVER DRAINAGE 17. Beaver Dam Wash 1.2

FIGURE 1.—Delineation of the Lahontan basin (I), Death Valley system (II), and Colorado River drainage (III), and locations (numbered 1-17) of Rhinichthys osculus populations examined in morphological and genetic studies. Super- script 1 on place names denotes museum collections examined in morphological studies; superscript 2 denotes populations sampled for genetic analysis.

Methods them from Pine and Rock creeks and the other Morphological and allozyme analyses were con- from A-1 Drain, were combined), and 14 collections ducted on several speckled dace populations from from 13 localities were used for analysis of meristic the Lahontan basin, one population from the lower and mensural characteristics. Colorado River drainage, and all known popula- Morphometrics.—Eighteen traditional truss mea- tions in the DVS (Figure 1). Of the 17 collections surements, fin lengths, and six meristic variables examined, 13 were used for the allozyme analysis (lateral line scales and pores and rays of the dorsal, (two proximate collections near Bishop, one of anal, pelvic, and pectoral fins, all counted by the 352 SADA ET AL.

FIGURE 2.—Morphometric measurements taken on speckled dace from the Death Valley system: (1) head width; (2) least bony interorbital width; (3) snout tip to supratemporal canal; (4) snout tip to branchiostegal junction; (5) branchiostegal junction to supratemporal canal; (6) supratemporal canal to pelvic fin origin; (7) supratemporal canal to dorsal fin origin; (8) branchiostegal junction to dorsal fin origin; (9) branchiostegal junction to pelvic fin origin; (10) dorsal fin origin to pelvic fin origin; (11) dorsal fin origin to anal fin origin; (12) pelvic fin origin to base last dorsal ray; (13) dorsal fin base length; (14) pelvic fin origin to anal fin origin; (15) base last dorsal ray to anal fin origin; (16) base last dorsal ray to upper caudal peduncle; (17) base last dorsal ray to lower caudal peduncle; (18) anal fin origin to upper caudal peduncle; (19) anal fin origin to lower caudal peduncle; (20) vertical through junction of caudal vertebrae 5 and 6 anterior of hypural plate; (21) depressed dorsal fin length; (22) depressed anal fin length; (23) pectoral fin length; (24) pelvic fin length; (25) standard length. Measurements 1-20 were used in sheared principle components analysis.

methods of Hubbs et al. 1974) were recorded from Isozyme data analysis. —Estimates of polymor- 484 fish (Figure 2). Individuals were segregated by phism and heterozygosity and tests for conformance sex for analysis of mensural characters, and only fish to Hardy-Weinberg expectations were made with longer than 25 mm standard length (SL) were ex- the BIOSYS-1 program (Swofford and Selander amined. Truss measurements and two measures of 1981). A X2 test for heterogeneity was used to test body width were analyzed by principal components the significance of allele frequency differences be- analysis with shearing to reduce the effects of size tween populations, and fixation (F) statistics were (Rohlf and Bookstein 1987). Components were calculated for all sampled populations. Differences sheared by locality and calculated from the covari- among populations were assessed by principal com- ance matrix of data transformed to basee loga- ponents analysis of arcsine-transformed allele fre- rithms. Proportional truss measurements (fractions quencies for polymorphic loci. of SL multiplied by 1,000), fin length measure- Distribution of endemic wetland species.—En- ments, and meristic counts were log-transformed demic wetland species associated with DVS valley (basee) and tested by one-way analysis of variance floor wetlands were identified from the literature (ANOVA) for differences among populations. and by consultation with regional scientists and land Protein electrophoresis.—The variability of iso- managers. zymes coded by 23 gene loci (Table 1) was assayed for 311 speckled dace from 13 localities (Figure 1). Whole fish were stored at -80°C until processed for Results electrophoresis. Approximately 1 g of muscle tissue Morphological Analysis was dissected from the caudal end of each fish. This was minced in an iced spot plate and combined with Meristic and proportional mensural characters 0.75 mL of chilled 0.05 M tris-HC1 extraction buffer were all within ranges documented for speckled (pH 7.1) in a centrifuge tube for further macera- dace (Hubbs et al. 1974). Highly significant differ- tion. Electrophoretic and histochemical staining ences among all populations for all meristic and procedures followed those of May (1992). mensural characters (P < 0.001, one-way ANOVA) DIVERSITY OF DESERT POPULATIONS 353

TABLE 1.—Enzymes and their abbreviations (Shaklee et al. 1990), enzyme numbers (IUBMBNC 1992), and buffers (May 1992) used in electrophoretic analysis of speckled dace. Enzyme Number Enzyme Abbreviation' number of loci Buffer

Asparate aminotransferase sAAT 2.6.1.1 Creatine kinase CK 2.7.3.2 Esterase EST 3.1.1.- 2 General (unidentified) protein PROT 3 Glycerol-3-phosphate dehydrogenase G3PDH 1.1.1.8 1 Glucose-6-phosphate 1-dehydrogenase G6PHD 1.1.1.49 1 Glucose-6-phosphate isomerase GPI 5.3.1.9 2 Isocitrate dehydrogenase (NADP') IDH 1.1.1.42 L-Lactate dehydrogenase LDH 1.1.1.27 2 4 Malic enzyme (NADP') sMEP 1.1.1.40 1 4 Mannose-6-phosphate isomerase MPI 5.3.1.8 1 4 Dipeptidase PEPA 3.4.-.- 1 Tripeptide aminopeptidase PEPB 3.4.-.- 1 Proline dipeptidase PEPD 3.4.-.- 1 Phosphogluconate dehydrogenase PGDH 1.1.1.44 1 4 Phosphoglucomutase PGM 5.4.2.2 2 4 Superoxide dismutase sSOD 1.15.1.1 aAn "s" prefix specifies the cytosolic form of the enzyme.

showed the morphology of each population to be 0.05, x2 tests), indicating substantial genetic differ- unique. entiation among populations. Furthermore, the Plots of sheared principal components II and III mean fixation index, FsT, among the 13 populations indicated that the body shapes of both males and was 0.538 and the mean index for individuals, FIT, females segregated strongly in some populations was 0.621. A hierarchical analysis to elucidate the but could not be differentiated in others. The most geographical scale at which panmixia breaks down definitive patterns of body shape appeared when showed significant allele frequency differences (P < factor scores of strongly overlapping populations 0.05) among the four populations within the Owens were clustered (Figure 3). These plots suggest that River drainage at six of the eight polymorphic loci body shape is best explained by the existence of two in the drainage (PGM-1*, PEPA*, sAAT*, EST-1*, forms, one that is short and deep and another that and GPI-1,2*). Likewise, all four polymorphic loci is long and slender. in the three Amargosa drainage populations (PGDH*, PGM-1*, sAAT*, and GPI-2*) differed Population Genetic Variability and Structure significantly in allele frequencies (P < 0.05). Signif- Only Smoke Creek (sAAT* locus), Bishop (PGM- icant differences in allele frequencies were detected 1*), and Huntington Creek (PGD-1* and PEPD*) between the two Smoke Creek populations at two populations were not in Hardy–Weinberg equilib- of the four polymorphic loci (PGM-1* and GPI-1*; rium at all assayed loci. P < 0.05). When the two Smoke Creek populations All populations were fixed for the same alleles at were tested for allele frequency heterogeneity with the remaining monomorphic loci except for those in the two Humboldt populations, significant levels of the Owens basin at Whitmore Hot Springs and heterogeneity occurred at eight of the nine poly- Little Alkali Lake. The alternative (*D) allele of the morphic loci in these populations (PGDH*, PGM- PEPA* locus segregated in these populations, pro- 1*, MPI*, PEPD*, sAAT*, CK*, EST-1*, and GPI- viding the only instances in which populations were 1*; P < 0.05). There were no detected differences in distinguished by a fixed allelic difference. allele frequencies between the Reese River and Polymorphism levels ranged from 4% in lower Huntington Creek populations (two Humboldt Marble Creek and Little Alkali Lake samples to drainage populations from the Lahontan basin). 35% in the Huntington Creek population (Table 2). This indicates that a higher level of gene flow may Mean observed heterozygosity ranged from 0.008 in be occurring between the Humboldt drainage pop- the Little Alkali Lake population to 0.072 in the ulations than among DVS populations. Finally, the East Fork Walker River sample (Table 2). population-to-drainage fixation index (F) was 0.525 Differences in allele frequencies among popula- and the population-to-total sample fixation index tions were significant for all polymorphic loci (P < was 0.528, indicating that gene flow among these

354 SADA ET AL.

0.25

0.15

0.1 0.7 0.75 0.8 0.85 0.9 0.95 1 PCII

0.25

0.2 = 5 0. 0.15

0.1

0.05 0.6 0.65 0.7 0.75 0.8 0.85 0.9 0.95 PCII 0 DEEP BODY • SLENDER BODY

FIGURE 3.—Plots of factor scores along sheared principal components (PC) II and III, clustered by body type, for 484 Death Valley system, Lahontan basin, and lower Colorado River speckled dace Rhinichthys osculus. (a) females; (b) males.

populations is approximately the same within drain- rado River populations should be conducted to re- ages as between drainages. solve questions about speckled dace diversity in this Factor score plots from analysis of principal com- river system. ponents illustrate the genetic differences and rela- tionships among the sampled populations (Figure Other Tam Endemic to Death Valley Wetlands 4). Death Valley system populations cluster sepa- rately from Lahontan basin populations. This indi- Fifty-nine plant and taxa are documented cates that ancestral DVS speckled dace invaded this from wetland and aquatic habitats in the DVS (Ta- basin from the Colorado River rather than from the ble 3). This includes 10 plant taxa (Morefield and Lahontan basin. Additional studies involving Colo- Knight 1992; Hickman 1993), 3 mammals (Hall and DIVERSITY OF DESERT POPULATIONS 355

TABLE 2.-Genetic variability estimates for 13 populations of speckled dace sampled in California and Nevada. Standard errors are in parentheses. Mean (SE) heterozygosity Mean (SE) Percentage 4. number of of loci Hardy-Weinberg Population alleles per locus polymorphic Direct count expectation Upper Smoke Creek 1.1 (0.1) 13.0 0.049 (0.028) 0.054 (0.030) Lower Smoke Creek 1.3 (0.1) 17.4 0.054 (0.027) 0.071 (0.037) Reese River 1.4 (0.1) 30.4 0.067 (0.026) 0.084 (0.035) Huntington Creek 1.5 (0.2) 34.8 0.056 (0.020) 0.102 (0.037) East Fork Walker River 1.4 (0.2) 30.4 0.072 (0.029) 0.078 (0.031) Whitmore Hot Spring 1.1 (0.1) 8.7 0.029 (0.020) 0.028 (0.020) Little Alkali Lake 1.0 (0.0) 4.3 0.008 (0.008) 0.008 (0.008) Lower Marble Creek 1.0 (0.0) 4.3 0.017 (0.017) 0.020 (0.020) Bishop, California 1.3 (0.1) 21.7 0.028 (0.015) 0.045 (0.024) Tecopa, California 1.1 (0.1) 8.7 0.023 (0.016) 0.029 (0.021) Ash Meadows 1.1 (0.1) 8.7 0.014 (0.013) 0.020 (0.015) Beatty, Nevada 1.1 (0.1) 8.7 0.011 (0.009) 0.011 (0.009) Beaver Dam, Washington 1.2 (0.1) 8.7 0.040 (0.028) 0.035 (0.024)

Kelson 1959), 7 aquatic insects (Polhemus 1979; speckled dace, many inhabit wetland communities Schmude 1992; Shepard 1992), 22 mollusks (Hershler some distance from fish habitats. and Sada 1987; Hershler 1989), 1 amphibian (Steb- bins 1966), and 16 fish (Smith 1978; Soltz and Discussion Naiman 1978). Habitat occupied by these species is either aquatic (fish, mollusks, and insects), mesic Several people have used isozyme data to esti- alkali meadow (plants and mammals), or semiter- mate population structure and levels of gene flow restrial (mollusks and amphibians). Although distri- between populations (e.g., Slatkin 1985; Allendorf butions of many of these taxa overlap with DVS et al. 1987). The isolation of desert wetlands sug-

2 • Beatty 1.5 * Beaver Dam Wash

Huntington Creek 0.5 A A Reese River • Marble Creek A Smoke Creek - 16.8% 0 . Bishop & Pine/Rock Creeks

PC II AEast Fork -0.5 N Bradford Spring Walker River • Tecopa -1 • Little Alkali Lake

-1.5 / Whitmore Hot Springs

-2.5 -2 -1.5 -0.5 0 0.5 1.5 2 2.5 PC 1 - 26.7% A Lahontan Basin • Death Valley System * Lower Colorado River FIGURE 4.-Principal components (PC) plot of arcsine-transformed allele frequencies in 13 speckled dace populations assayed in the Death Valley system, Lahontan basin, and lower Colorado River. 356 SADA ET AL.

TABLE 3.—Endemic taxa of valley floor wetlands in the Owens, Amargosa, and Mojave basins and Death Valley. Habitat abbreviations: ST = stream, SP = spring source, SPMAR = spring margin, MAM = mesic alkali meadow, MAF = mesic alkali flat. Taxon Habitat

Owens River Basin Plants Owens Valley checkerbloom Sidalcea covellii MAM Fish Slough milkvetch Astragalus lentiginosus var. piscensis MAM Owens Valley Mariposa lily Calochortus excavatus MAM Mollusks Owens springsnail owensensis SP Fish Slough springsnail Pyrgulopsis perturbata SP Benton Valley springsnail Pyrgulopsis aardhali SP Fish Owens radiosus SP, ST Owens tui chub Gila bicolor snyderi ST Long Valley speckled dace Rhinichthys osculus ssp. SP, ST Owens speckled dace Rhinichthys osculus ssp. ST Owens sucker Catostomus fumeiventris ST Mammals Owens Valley vole Microtus californicus vallicola Amargosa River Basin Plants Ash Meadows ivesia Ivesia eremica MAF Ash Meadows gumplant Grindelia fraxino-pratensis SPMAR Ash Meadows ladies tresses Spiranthes infernalis SPMAR Amargosa nitenvort Nitrophila mohavensis MAF Spring-loving centaury Centautium namophilune SPMAR Tecopa birds beak Cordylanthus tecopensis MAM Insects Devils hole riffle beetle Stenelemis calida calida SP Amargosa naucorid bug amargosus SP Relict naucorid bug Ambrysus sp. SP Saratoga Springs bug Belostoma saratogae SP (No common name) Microcylleopus similis SP Mollusks . Sporting,goods tryonia Tryonia anuglata SP (No common name) Tryonia variegata SP (No common name) Tryonia ericae SP Point of Rocks tryonia Tryonia elata SP Fairbanks Spring springsnail Pyrgulopsis fairbanksensis SP Crystal Spring springsnail Pyrgulopsis crystalis SP Longstreet Spring springsnail Pyrgulopsis sp. SP Oasis Valley springsnail Pyrgulopsis micrococcusb SP Ash Meadows pebblesnail Pyrgulopsis erythropoma SP Distal-gland springsnail Pyrgulopsis nanus SP Median-gland springsnail Pyrgulopsis pisteri SP Elongate-gland springsnail Pyrgulopsis isolatus SP Amargosa springsnail Pyrgulopsis amargosae SP (No common name) sp. SPMAR Fish Cyprinodon diabolis SP Ash Meadows Nevada pupfish mionectes SP Cyprinodon nevadensis nevadensis SP Warm Springs pupfish Cyprinodon nevadensis pectoralis SP Cyprinodon nevadensis tecopensis SP Cyprinodon nevadensis shoshone SP Nevada speckled dace Rhinichthys osculus nevadensis SP, ST Ash Meadows poolfish Empetrichthys merriami SP Mammals Ash Meadows vole Microtus montanus nevadensis Amargosa vole Microtus californicus scitpensis Amphibians Amargosa toad Bufo nelsoni SPMAR DIVERSITY OF DESERT POPULATIONS 357

TABLE 3.—Continued. Taxon Habitat

Death Valley Plants Death Valley blue-eyed grass Sisyrinchium funereum SPMAR Insects (No common name) Ambrysus funebris SP (No common name) Microcylleopus formicoideus SP Mollusks Assiminea infima SPMAR Grapevine Springs elongate tryonia Tryonia margae SP Grapevine Springs squat tryonia Tryonia rowlandsi SP Robust tryonia Tryonia robusta SP Cottonball Marsh tryonia Tryonia sauna SP Fish Salt Creek pupfish Cyprinodon salinus salinus SP, ST Cottonball Marsh pupfish Cyprinodon salinus milleri SP Mojave River Basin Fish Mojave tui chub Gila bicolor mohavensis ST 'Also occurs in Death Valley. bAlso occurs in the Mohave River basin. gests that genetic diversity within populations occu- timates for most DVS speckled dace populations is pying these habitats should be low but that many consistent with the hypothesis that neutral or populations should be genetically distinctive (Meffe weakly selected genetic variability is lost due to and Vrijenhoek 1988). These assumptions have genetic drift in small isolated populations. The been confirmed by Turner (1974) and Echelle and mean heterozygosity over DVS populations (0.014) Echelle (1993) in work with pupfish (genus Cyprin- was substantially lower than heterozygosities in La- odon) throughout the southwestern United States, hontan basin and lower Colorado River popula- including the DVS. tions, which were near the average documented for Earlier workers recognized the distinctiveness of other cyprinid fishes (0.052; Buth et al. 1991). Even speckled dace populations within isolated Great though the morphological distinctiveness of each basin drainages (Hubbs and Miller 1948; Hubbs et DVS speckled dace population is clouded by the al. 1974). Data from our study indicate that speck- presence of only two body forms, differences in led dace variation conforms more to relatively re- meristic and mensural characteristics among popu- cent models (Slatkin 1985; Allendorf et al. 1987) lations also suggest that each population is distinc- that recognize the distinctiveness of individual pop- tive. Recognition of the taxonomic distinctiveness ulations than to earlier models that recognized dis- of many regional fishes has justified protection of tinctiveness only by focusing on similarities among many aquatic habitats throughout the desert South- populations in a basin. We used Slatkin's (1987) west (Williams and Sada 1985; Williams et al. 1985). method with our data to calculate the genetically However, no population of aquatic species in this effective number of migrants between all popula- region has been protected unless it had gained for- tions for each generation (N„,) from FS, values. mal taxonomic recognition. Our genetic and mor- The results indicate that approximately one genet- phological examination indicates that populations ically effective individual is exchanged per DVS of even wide-ranging species may be unique and population every five generations (Nm = 0.21). This worthy of protection as evolutionarily significant level of gene flow is well below the level theoreti- units. cally necessary to prevent populations from diverg- The number and diversity of species endemic to ing in allele frequencies under a neutral model of DVS wetlands suggest that factors causing the ge- selection (Hartl and Clark 1989). The significant netic and morphological differentiation of DVS differences in allele frequencies and the fixation of speckled dace have also affected a wide diversity of a unique allele at PEPA* in the Whitmore Hot plants and animals. Isolation and differentiation Springs and Little Alkali Lake populations further have permitted development of unique communi- indicate a paucity of gene flow between DVS pop- ties associated with each persistent water. ulations. Also, the relatively low heterozygosity es- The biotic distinctiveness of these isolated waters 358 SADA ET AL. requires conservation programs to be designed wetlands suggests that programs conserving these around ecological requirements of the entire com- species must be ecologically based on communities. munity. Williams et al. (1985) and Moyle and Yo- This lesson can also be applied to conservation of shiyama (1994) have proposed protective strategies wetland systems in more mesic regions. The chal- that embrace a broad variety of aquatic species. lenge of conservation requires more than protecting However, both these strategies focus attention on a population in the isolation of its immediate envi- aquatic species; neither addresses the broader re- ronment. It also requires conserving populations as quirement of protecting communities that rely upon a part of their ecosystem so they can continue along adjacent mesic soils as well as upon water. The their evolutionary pathways. ecology and distribution of species endemic to DVS wetlands suggests that conservation programs fo- Acknowledgments cusing upon only aquatic species may not be ade- quate. More definitive protective strategies should Genetics and morphology analyses were sup- ported by funds from the California Department of consider the entire ecosystem and be implemented Fish and Game's Endangered and Rare Fish, Wild- to include the entire community of organisms reli- ant upon waters supporting the aquatic habitat. In life, and Plant Species Conservation Account (con- this respect, tasks for these conservation programs tract FG0524), and assistance from the Nevada should be expanded beyond those necessary to Biodiversity Initiative. Live material was collected maintain aquatic ecosystems and include tasks nec- under California Department of Fish and Game essary to maintain habitats in the broader context of permit 279, Nevada Department of Wildlife permit wetlands. 6923, and U.S. Fish and Wildlife Service Endan- The importance of recognizing the diverse taxa gered Species Permit SADADW issued to D. Sada. associated with aquatic habitats is supported by Mary DeDecker and Anna Halford assisted with examining the ecology of several DVS endemic spe- identifying endemic DVS plant taxa. cies. The Amargosa niterwort is restricted to mesic alkali flats in the Amargosa basin (Mozingo 1977), References where most populations rely on soil moisture that is Allendorf, F. W., N. Ryman, and F. M. Utter. 1987. Ge- maintained by discharge from springs approxi- netics and fishery management: past, present, and mately 8 km away. This plant could be detrimentally future. Pages 1-19 in N. Ryman and F. Utter, editors. affected by narrowly conceived conservation pro- Population genetics and fishery management. Univer- grams that inadvertently alter soil moisture and sity of Washington Press, Seattle. subsurface percolation in areas distantly associated Brues, C. T. 1932. Further studies on the fauna of North American hot springs. Proceedings of the American with aquatic habitats. Although many endemic DVS Academy of Arts and Sciences 67:184-303. taxa occupy terrestrial habitats close to flowing wa- Buth, D. G., T. E. Dowling, and J. R. Gold. 1991. Mo- ter, the population viability of most endemic plants, lecular and cytological investigations. Pages 83-126 in mammals, and mollusks (e.g., Assiminea infima) de- I. J. Winfield and J. S. Nelson, editors. Cyprinid fishes pends upon mesic soils moistened by water from systematics, biology, and exploitation. Chapman and sometimes distant springs and streams. Ecological Hall, London. Echelle, A. A., and A. F. Echelle. 1993. Allozyme per- diversity represented by the complete community of spective on tnitochondrial DNA variation and evolu- endemic DVS species suggests that programs de- tion of the Death Valley (Cyprinodontidae: signed to conserve these species would protect all Cyprinodon). Copeia 1993:275-287. aspects of wetland ecosystems in the region. We Hall, E. R., and K. R. Kelson. 1959. Mammals of North believe the uniqueness of these communities qual- America. Ronald Press, New York. ifies each as an evolutionarily significant unit. Hartl, D. L., and A. G. Clark. 1989. Principles of popu- lation genetics, 2nd edition. Sinauer, Sunderland, Much of the knowledge about desert wetland Massachusetts. ecosystems comes from comparatively recent stud- Hershler, R. 1989. Springsnails (: Hydrobi- ies of their species' ecology, genetics, and mor- idae) of Owens and Atnargosa River (exclusive of phometry. The diversity of taxa dependent upon Ash Meadows) drainages, Death Valley system, Cali- these aquatic resources is much greater than was fornia—Nevada. Proceedings of the Biological Society appreciated before these studies began. Additional of Washington 102:176-248. Hershler, R., and D. W. Sada. 1987. Springsnails (Gas- surveys and continued advances in and tropoda: ) of Ash Meadows, Amargosa ecology are necessary to define tasks that will con- basin, California—Nevada. Proceedings of the Biolog- serve all members of these wetland communities. ical Society of Washington 100:776-843. The diversity of organisms that depend on desert Hickman, J. C., editor. 1993. The Jepson manual. Higher DIVERSITY OF DESERT POPULATIONS 359

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