Aspidoscelis Exsanguis Research Articles

Whiptail lizards (Aspidoscelis exsanguis) recognize invertebrate prey via cuticular hydrocarbons

AbstractCuticular hydrocarbons (CHCs) present on the surface of arthropods are important mediators of both intraspecific and interspecific interactions. They are known to be important chemical cues that help predatory arthropods locate prey, yet less is known about if and how vertebrate insectivores use these nearly ubiquitous chemical cues. We examined behavioral responses of insectivorous lizards (Aspidoscelis exsanguis) to the CHCs of three different species of arthropod prey (crickets, ants, and spiders). We presented cotton swabs with either extracted CHCs or a solvent control to determine if lizards respond to CHCs in the absence of visual cues of prey. We found that CHCs not only increased the frequency of chemosensory behaviors performed by predatory lizards, but that they also elicit feeding‐like behavior from lizards (e.g., biting at the cotton swabs). These results indicate that lizards not only respond to arthropod CHCs, but that they are sufficient for prey‐recognition by our chosen lizard species. This finding lays the ground work for future studies to investigate the precise compounds that are used by foraging lizards, and how the chemical communication systems of arthropods respond to selection exerted by vertebrate predators.

Predatory lizards perceive plant-derived volatile odorants.

Many lizards are olfactory foragers and prey upon herbivorous arthropods, yet their responses to common herbivore‐associated plant volatiles remain unknown. As such, their role in mediating plant indirect defenses also remains largely obscured. In this paper, we use a cotton‐swab odor presentation assay to ask whether lizards respond to two arthropod‐associated plant‐derived volatile compounds: 2‐(E)‐hexenal and hexanoic acid. We studied the response of two lizard species, Sceloporus virgatusand Aspidoscelis exsanguis, because they differ substantially in their foraging behavior. We found that the actively foraging A. exsanguisresponded strongly to hexanoic acid, whereas the ambush foraging S. virgatus responded to 2‐(E)‐hexenal—an herbivore‐associated plant volatile involved in indirect defense against herbivores. These findings indicate that S. virgatus may contribute to plant indirect defense and that a species' response to specific odorants is linked with foraging mode. Future studies can elucidate how lizards use various compounds to locate prey and how these responses impact plant‐herbivore interactions.

Corrigenda: Davis DR, LaDuc TJ (2018) Amphibians and reptiles of C. E. Miller Ranch and the Sierra Vieja, Chihuahuan Desert, Texas, USA. ZooKeys 735:97-130. https://doi.org/10.3897/zookeys.735.22200.

[This corrects the article DOI: 10.3897/zookeys.735.22200.].

Neaves' Whiptail Lizard: The First Known Tetraploid Parthenogenetic Tetrapod (Reptilia: Squamata: Teiidae)

Abstract The first known tetraploid amniote that reproduces through parthenogenetic cloning by individual females is named and described. The species originated through hybridization between Aspidoscelis exsanguis (triploid parthenogen) × Aspidoscelis inornata (diploid bisexual or gonochoristic species) in the laboratory. We compared multivariate morphological variation between two lineages that arose from separate F1 hybrid zygotes in one clutch and among several generations in those lineages. The tetraploid species is also compared with its ancestral taxa, with two hybrids of A. exsanguis × A. inornata that were found in nature at two localities that are 100 km apart in southern New Mexico, and with three laboratory hybrid males. This will facilitate identification of field-caught tetraploids in the future.

Extreme variant of the triploid parthenogenetic lizardAspidoscelis exsanguis(Squamata: Teiidae) from New Mexico

Abstract Parthenogenetic reproduction in several all-female species of whiptail lizards (genus Aspidoscelis) does not preclude the occasional production of extreme variants. An adult lizard with a unique combination of dorsal color pattern, scutellation, and meristic characters captured 20 August 2013 approximately 200 m east of the Rio Grande in Bosque Farms, Valencia County, New Mexico, was inferred to be an extreme variant of triploid, hybrid-derived Aspidoscelis exsanguis which was also observed near the point of capture. There was no basis for identifying the specimen as a tetraploid hybrid because morphology did not reflect that origin and no gonochoristic species (e.g., Aspidoscelis marmorata or Aspidoscelis inornata) was known to occur at the site. Morphological analyses also ruled out the possibility that it could be an extreme variant of diploid parthenogenetic Aspidoscelis neomexicana, which is syntopic with A. exsanguis in Bosque Farms.

Growth, Activity, and Survivorship from Three Sympatric Parthenogenic Whiptails (Family Teiidae)

We surveyed whiptail lizard populations for seven summers (2000–2006) in riparian forests along the Rio Grande in central New Mexico. We captured 5,382 individuals from three parthenogenic species (Aspidoscelis exsanguis, Aspidoscelis neomexicana, and Aspidoscelis uniparens) including 129 hatchlings (young-of-the-year) that were later recaptured as adults. Growth data were fit to a logistic growth model and compared using a likelihood ratio test. Comparisons of growth rates showed that A. exsanguis grew faster than both A. neomexicana and A. uniparens and attained a larger snout–vent length (SVL). Comparisons of capture rates showed that species had similar activity patterns during the summer. Captures of adults peaked in mid-June and decreased in August. Hatchlings became active at the end of July and captures peaked in September. Some individuals were captured several seasons indicating that lizards lived for at least 3–4 yr. Our study shows both similarities and differences in life-history characteristics for three closely related and coexisting whiptail species.

Strong Artifactual Effect of Starting Distance on Flight Initiation Distance in the Actively Foraging Lizard Aspidoscelis exsanguis

Escape theory predicts flight initiation distance (FID), distance between predator and prey when escape begins, for factors affecting costs of fleeing and not fleeing. Starting distance (SD), distance between predator and prey when approach begins, appears to affect FID for some species and risk levels, but not others. I predicted that in an active forager under low risk FID would appear to increase as SD increases due to (1) inclusion of SDs shorter than optimal FID and (2) spontaneous movements not motivated by escape. I predicted that FID and SD are unrelated at low risk when SDs shorter than optimal FID and spontaneous movements are excluded. When I approached the lizard Aspidoscelis exsanguis, an active forager, all predictions were confirmed. Effects of short SD and spontaneous movement might account for relationships between FID and SD in some birds and lizards. Nevertheless, as a predator approaches, costs of monitoring may increase, as may assessed risk and risk-averse errors due to shorter available assessment time. Risk-aversion might account for restriction of the relationship between FID and SD to high risk levels in an ambushing lizard species, for which spontaneous movements are far less frequent than for active foragers such as A. exsanguis. Although FID and SD are unrelated in A. exsanguis, SD and the related alert distance can provide valuable insights into risk assessment in other taxa having escape movements distinct from other movements. Present findings emphasize the importance of distinguishing between escape and other movements that may be initiated during approaches. A previously untested prediction of escape theory is that escape begins immediately when a prey detects an approaching predator closer than optimal FID, leading to the prediction of a slope of 1.0 between FID and SD. This prediction was confirmed for SDs less than 1.5 m.

COMPARATIVE ESCAPE BEHAVIOR OF CHIHUAHUAN DESERT PARTHENOGENETIC AND GONOCHORISTIC WHIPTAIL LIZARDS

We characterized differences in escape behavior among syntopic parthenogenetic and gonochoristic whiptail lizards (Teiidae: Aspidoscelis) in western Texas by performing 2 experiments. The first experiment revealed that Aspidoscelis exsanguis (parthenogenetic) allowed a human simulated predator to approach significantly closer than Aspidoscelis neomexicana (parthenogenetic), and both species allowed a significantly closer approach than Aspidoscelis tigris (gonochoristic). Furthermore, A. neomexicana and A. exsanguis did not flee as far as A. tigris, but this difference in flight distance was not statistically significant. Temperature was not correlated with approach distance or flight distance for any of the above species. The second experiment determined that, when captured, Aspidoscelis tesselata (parthenogenetic) was more likely to release cloacal contents on a human captor than A. tigris (gonochoristic).

Hybridization Between Parthenogenetic Lizards (Aspidoscelis neomexicana) and Gonochoristic Lizards (Aspidoscelis sexlineata viridis) in New Mexico: Ecological, Morphological, Cytological, and Molecular Context

Whiptail lizard guilds consisting of different combinations of parthenogenetic Aspidoscelis exsanguis, Aspidoscelis neomexicana, and Aspidoscelis tesselata pattern classes C and D and gonochoristic Aspidoscelis sexlineata viridis inhabit numerous sites in the immediate vicinity of Conchas Lake, San Miguel County, New Mexico. Based on morphological identification by other workers of specimens collected in 1978, A. neomexicana was the species most recently added to the list of whiptail lizards known to occur at Conchas Lake, about 190 km east of its main distribution area in the Rio Grande Valley. We sampled guilds consisting of A. neomexicana and its congeners at Conchas Lake from 2000 through 2003. In 2002 we also collected specimens of what appeared to be another tokogenetic array of A. neomexicana east of the Rio Grande Valley in syntopy with A. tesselata E and A. sexlineata viridis at Fort Sumner, De Baca County, New Mexico. Comparison of karyotypes revealed that individuals of A. tesselata and those assigned by their discoverers to A. neomexicana from Conchas Lake and Fort Sumner have identical diploid karyotypes (2n = 46) that include diagnostic haploid complements of chromosomes derived from independent hybridizations between species in the tigris and sexlineata species groups. Consequently, we used electrophoretic data for 23 gene loci, of which the sMDH, sMDHP, sIDH, ESTD, PEPA, PEPB, ADA, MPI, GPI, and PGM2 loci were definitive, to further validate the hypothesis that the disjunct groups of putative A. neomexicana in eastern New Mexico had been correctly identified. The specimens analyzed electrophoretically also indicated that the Conchas Lake clone of A. neomexicana is identical to the most widely distributed clone of the species in the Rio Grande Valley of New Mexico and that the Fort Sumner clone possessed a distinctive allele.We describe the habitat for A. neomexicana at Conchas Lake at three sites north of the Canadian River and two sites south of the river. Two of the sites north of the Canadian River were studied as examples of guilds that did not include A. sexlineata viridis. The latter species was observed with A. neomexicana, A. tesselata, and A. exsanguis at one site north of the Canadian River and two sites south of the river. At Fort Sumner, we studied A. neomexicana at two sites where it was syntopic with A. tesselata E and A. sexlineata viridis.We identified 15 lizards from three sites at Conchas Lake as hybrids of A. neomexicana × A. sexlineata viridis. Most of these hybrids were found in either patchy or weedy chronically disturbed habitats in which the parental forms were forced into unusually close syntopic relationships. Hybrids between these parental forms were collected in each year from 2000– 2003 and represented a minimum of four and a maximum of five generations.Although hybrids of A. neomexicana × A. sexlineata viridis were characterized by distinctive color patterns, all were rather similar to maternal parent A. neomexicana, but with modifications resulting from the genetic contribution of its paternal parent A. sexlineata viridis. All specimens identified as hybrids by color pattern also possessed meristic characters that distinguished them from both parental forms. Univariate and multivariate analyses of scutellation also revealed evidence of the genetic effects of the parental species on the hybrids.One live hybrid male of A. neomexicana × A. sexlineata viridis was collected at Conchas Lake. The hybrid (American Museum of Natural History R-151739) was a triploid (3n = 69) including the complete diploid complement of A. neomexicana (= A. tigris marmorata × A. inornata) plus a second haploid complement of sexlineata group chromosomes. Karyotypically, in all details this triploid appeared to be an F1 hybrid of A. neomexicana × A. sexlineata viridis. This confirmed hybrid possessed a similar array of color pattern and scutellation characters observed in the other individuals of presumptive

NOCTURNAL ACTIVITY BY DIURNAL LIZARDS (SCELOPORUS JARROVI, S. VIRGATUS) EATEN BY SMALL OWLS (GLAUCIDIUM GNOMA, OTUS TRICHOPSIS)

Whiskered screech-owls (Otus trichopsis) and northern pygmy-owls (Glaucidium gnoma) delivered freshly caught Yarrow's spiny lizards (Sceloporus jarrovi) and striped plateau lizards (S. virgatus) to nestlings from dusk to dark in southeastern Arizona. This observation stimulated studies of the prey deliveries by the owls and lizard activity patterns, because the lizards are not known to be nocturnal. Lizards were more frequent prey of both owls than endothermic vertebrates but infrequent compared to arthropods, a pattern in the pygmy-owl that differs from its northern populations. Yarrow's spiny lizard, the most abundant and frequently captured lizard, was most active in the morning but also active in the evening. Striped plateau lizard, the second most abundant and depredated species, had morning and evening peaks of activity. Few lizards, including S. clarki and Urosaurus ornatus, but not Cnemidophorus exsanguis and C. sonorae, were active at or after dark, when relatively few were captured by the owls.

Natural Hybridization Between the Teiid Lizards Cnemidophorus tesselatus (Parthenogenetic) and C. tigris marmoratus (Bisexual): Assessment of Evolutionary Alternatives

Annual hybridization is taking place between representatives of the parthenogenetic lizard Cnemidophorus tesselatus (2n = 46, 47) and males of the bisexual species C. tigris marmoratus (2n = 46) in desert grassland habitats at Arroyo del Macho, Chaves County, New Mexico. This raises the question of whether a new triploid parthenogenetic species may be originating as a consequence of this activity. Hybrids were collected in each of four years (1996–1999), and 20 of 21 hybrids collected (12 males and 8 females) were available for study. Although a triploid parthenogenetic species (Cnemidophorus exsanguis 3n = 69) and a diploid bisexual species (C. inornatus 2n = 46) were also found at the hybridization site, the genealogy of the hybrids was determined unequivocally with karyotypic and electrophoretic evidence (34 loci tested). The specimens examined electrophoretically included an adult female and one of her laboratory-reared daughters, which demonstrated for the first time clonal inheritance in C. tesselatus pattern class E.The population of C. tesselatus at Arroyo del Macho is characterized by two karyotypic cytotypes. The ancestral one (2n = 46) occurs at about half the frequency of the derived cytotype (2n = 47), which apparently was produced by centric fission of the ancestral X-chromosome from C. tigris In contrast, the occurrence of the two cytotypes was reversed and strongly asymmetrical in the hybrids; only one of nine hybrids possessed the fissioned X-chromosome. This individual was significantly different in 12 meristic characters from the sample of hybrids with intact X-chromosomes. Predictably, principal components scores for this individual fell outside the 95% confidence ellipse of scores of the other eight hybrids that were karyotyped. The skewed ratio and multiple phenotypic differences suggest that hybrids inheriting a fissioned X-chromosome might be at a selective disadvantage compared to hybrids with intact X-chromosomes.All 20 hybrids closely resemble C. tesselatus in most color pattern features. However, these hybrids, like C. tigris marmoratus lack lateral stripes. Because the population of C. tesselatus at Arroyo del Macho has lateral stripes (or their remnants), hybrids can be readily distinguished from C. tesselatus by this color pattern feature. Compared to the two parental species, hybrids had a significantly lower mean number of scales around midbody, but hybrids resembled either C. tesselatus or C. tigris marmoratus in other univariate meristic characters. This mosaic pattern of resemblance was simplified to a three-dimensional depiction of variation using principal components analysis. Each of two principal components expressed the resemblance of hybrids to one of the two parental species. A third component reflected the difference between hybrids and both parental species. A canonical variate analysis of meristic characters demonstrated the multivariate distinctiveness of each group—hybrids, C. tesselatus and C. tigris marmoratus However, based on Mahalanobis D2 distances, the closest morphological resemblance among hybrids and parental species was between hybrids and the maternal species, C. tesselatusNine additional museum specimens, suspected of being C. tesselatus × C. tigris marmoratus hybrids, were identified, as such, by a canonical variate analysis using our samples of C. tesselatus, C. tigris marmoratus and hybrids from Arroyo del Macho as a priori groups. These nine individuals document hybridizations between C. tesselatus and C. tigris marmoratus at two additional localities in Chaves County, New Mexico, two localities in Sierra County, New Mexico, and a cluster of sites near Presidio, Presidio County, Texas. Previously, several of these hybrids had been misidentified as male C. tesselatusThe reproductive systems of female and male hybrids were compared histologically to those of C. tesselatus and C. tigris marmoratus respectively. Sexually mature and reproductive adults of C. tesselatu

Helminth Parasites of Unisexual and Bisexual Whiptail Lizards (Teiidae) in North America. III. The Chihuahuan Spotted Whiptail (Cnemidophorus exsanguis)

Twenty-four of 87 (28%) parthenogenetic Chihuahuan spotted whiptails (Cnemidophorus exsanguis) from nine counties of New Mexico and seven counties of Texas were infected with one or more endoparasites. These included a linstowiid cestode (Oochoristica bivitellobata) in seven (8%), a larval spirurid nematode (Physaloptera sp.) in nine (10%) and an oxyurid nematode (Pharyngodon warneri) in 10 (11%). This note, the third in a series of reports on helminths of Cnemidophorus spp., documents parasites in C. exsanguis for the first time.

Tandem Duplication of D-Loop and Ribosomal RNA Sequences in Lizard Mitochondrial DNA

Some Cnemidophorus exsanguis have mitochondrial DNA's (mtDNA's) that are 22.2 kilobases (kb) in size, whereas most have mtDNA's of 17.4 kb. Restriction site mapping, DNA transfer hybridization experiments, and electron microscopy show that the size increment stems from the tandem duplication of a 4.8-kb region that includes regulatory sequences and transfer and ribosomal RNA genes. This observation is notable in that sequences outside of the control region are involved in major length variation. Besides revealing a novel form of mtDNA evolution in animals, these duplications provide a useful system for investigating the molecular and evolutionary biology of animal mtDNA.

Use of Anaerobic Metabolism by Free-Ranging Lizards

We measured whole-body lactic acid concentrations of two species of iguanid lizards and two species of teiids in the field during routine and experimentally manipulated activities. Lactate concentrations were lowest when lizards first emerged in the morning. Routine foraging behavior produced small increases in lactate concentrations for all species. The teiids (Cnemidophorus exsanguis and C. sonorae) had significantly higher lactate concentrations at emergence and during routine activity than did the iguanids (Sceloporus virgatus and S. jarrovi). For S. virgatus lactate concentration during routine activity was positively correlated with the distance a lizard moved (0-16 m) during the half-hour period of observation before capture. Subduing and swallowing grasshoppers increased lactate concentrations of S. virgatus by an average of .121 mg/g, which was an increase of 40% over the average for routine activity. The magnitude of the increase was positively correlated with the size of the prey (.09-.48 g) but not with the time required (<1-35 min). Territorial defense by S. jarrovi doubled the average lactate concentration from .309 mg/g during routine activity to .653 mg/g after combat. Intensity of combat (measured as bites per minute by the resident lizard) was positively correlated with lactate concentration, but the duration of an agonistic encounter (1-15 min) was not. These data suggest that anaerobic metabolism can be an important pathway of energy input for lizards under natural conditions and support the hypothesis that physiological constraints can limit the behaviors available to a species of lizard.

Additional notes on requirements of captive whiptail lizards (Cnemidophorus), with emphasis on ultraviolet radiation

AbstractSince 1972 we have maintained a colony of parthenogenetic Cnemidophorus exsanguis, which has reached the seventh generation in our laboratory. This paper reports improved husbandry techniques that allow maintenance of healthy, reproducing colonies of this and additional species of Cnemidophorus. In addition, aspects of the physiology of calcium regulation and metabolic bone disease are discussed in relation to the captive rearing of lizards through many generations.

Parthenogenetic reproduction in lizards: Histological evidence.

Hermaphroditism and sex reversal have not previously been ruled out adequately as possible explanations for the existence of unisexual species of reptiles. Therefore, we examined serial histological sections of the complete urogenital systems of nine F2 specimens belonging to two ontogenetic series of Cnemidophorus exsanguis raised in captivity in isolation from males, as well as the urogenital system of the F1 mother of one of these series. No evidence of spermatozoa or testicular tissue was found in any specimen. Comparative material reveals that the histology of the urogenital tract, including the mesonephric kidney in adults, is similar to that of females of bisexual species of Cnemidophorus. We conclude that C. exsanguis is a unisexual, parthenogenetic species whose normal reproduction does not involve sex reversal, self-fertilization, gynogenesis, hybridogenesis, or spermatozoa in any way whatsoever.

Analysis of the pH and Electrolyte Components Found in the Blood Plasma of Several Species of West Texas Reptiles

The pH and electrolytic composition of the plasma of several species of reptiles from Presidio Co., Texas, were investigated. Sodium, chloride and bicarbonate ions constitute over 80 per cent of the osmotically significant components of the plasma of these reptiles. Sodium ions constitute 91 per cent of the plasma cations. Bicarbonate and chloride ions account for 83 per cent of the total plasma anion concentration. The variability between the plasma electrolytes of these experimental animals was lowest for potassium. Data on plasma electrolyte levels is provided for the first time for Kinosternon flavescens, Cnemidophorus exsanguis, Crotalus molossus and Pituophis melanoleucus.

Ecological Relationships of Two Species of the Lizard Genus Cnemidophorus in the Santa Rita Mountains of Arizona

Ecological relationships of locally sympatric populations of the southern whiptail (Cnemidophorus tigris gracilis Baird and Girard), and the Chihuahua whiptail (Cnemidophorus exsanguis Lowe) on the Santa Rita Experimental Range, Arizona, were studied intermittently in 1962 and for their entire period of activity in 1963. Although analysis of stomach contents (consisting largely of termites) and daily activity pattern reveal little divergence between the two species, differences in foraging behavior may reflect differences in the kinds of food resources being exploited. Cnemidophorus exsanguis is an all-female species and has a clutch size half again as great as that of C. tigris. The indications are that competition does occur. About 20%o of the species belonging to the lizard genus Cnemidophorus (whiptail lizards) are uniparental, males being either unknown or extremely rare (Maslin, 1962, 1966). Three of the five species groups recognized within the genus include uniparental species, there being one such species for both the TESSELATUS and DEPPEI groups, and several in the SEXLINEATUS group. With the exception of Cnemidophorus cozumelus, which occurs on the Yucatan Peninsula of Mexico (and nearby islands), all of the uniparental species are restricted to an area from western Colorado and southeastern Utah to north-central Mexico, and from central Arizona to, western Texas. Few previous studies have been concerned with the ecology of the uniparental whiptails, possibly because of the uncertainty evident in the literature as to how uniparental species should be treated taxonomically (see, e.g., Maslin, 1966). Only M'ilstead (1953) has reported a comprehensive ecological study involving both unisexual and bisexual species of Cnemidophorus exsanguis. My paper reports such a study carried out with Cnemidophorus exsanguis Lowe (uniparental) and C. tigris gracilis Baird and Girard (bisexual). DISTRIBUTION AND HABITAT The overall geographic ranges of Cnemidophorus tigris gracilis and C. exsanguis overlap widely. Cnernidophorus tigris gracilis occurs in northeastern Sonora and northwestem Chihuahua, Mexico, in southwestern New Mexico (excluding the extreme southwestern corner of the state) and south-central and southeastern Arizona (excluding the extreme southeastern comer). Cnemidophorus exsanguis occupies about the same geographic range, but occurs more extensively in New Mexico than C. tigris gracilis (Stebbins, 1966). The study reported herein was carried out in the Santa Rita Mountains of southern Ari1 Present address: Museum of Natural History, University of Kansas, Lawrence 66044.

Species of the Cnemidophorus exsanguis Subgroup of Whiptail Lizards

Species of the Cnemidophorus exsanguis Subgroup of Whiptail Lizards

New Records for Reptiles from Chihuahua, Mexico, with Comments on Sympatry between two Species of Cnemidophorus

NEW RECORDS FOR REPTILES FROM CHIHUAHUA, MEXICO, WITH COMMENTS ON SYMPATRY BETWEEN TWO SPECIES OF CNEMIDOPHORUS.-The species mentioned below were collected during a brief collecting trip in the Mexican state of Chihuahua in July, 1962. Numbers refer to specimens in the collection of Ralph W. Axtell (RWA) or Robert G. Webb (RGW). We thank Hobart M. Smith for information concerning Tantilla atriceps. Cnemidophorus exsanguis Lowe and Cnemidophorus septemvittatus scalaris Cope.-Duellman and Zweifel (Bull. Amer. Mus. Nat. Hist., 123: 198, 1962) wrote that and west of Chihuahua City (the exact areas of contact remain to be discovered) C. s. scalaris is replaced by C. On a previous page, however, (op. cit.: 186) they mentioned the possibility of intergradation between C. exsanguis and C. septemvittatus on the Mexican Plateau. We found the two species sympatric at three localities-12 road mi. NW Cd. Chihuahua (2 scalaris, 2 exsanguis), 12 road mi. NW Est. Bachimba (27 road mi. NW of Meoqui, 7 scalaris, 3 exsanguis), and 10 road mi. NW Est. Bachimba (2 scalaris, 1 exsanguis). The four lizards from the first-mentioned locality are not included in the discussion below because the two exsanguis, presumably gravid, are being kept alive. Lizards from the last two localities are lumped for comparison between the two species. Duellman and Zweifel (op. cit.: 199) mentioned that several specimens of scalaris from near Meoqui, Chihuahua, resembled exsanguis, and, in the field, we initially identified several specimens of scalaris as exsanguis. Our four female exsanguis (RGW 2753-54; RWA 1084, 1086) range from 76 to 86 mm. in snout-vent length and closely resemble some scalaris of corresponding size in having whitish ventral surfaces and dorsal patterns of longitudinal stripes with spots in the dark fields. However, such individuals of exsanguis were distinguished from scalaris in having (1) the pale longitudinal stripes dim and obscure on the neck, often a uniform grayisholive (striping bright and prominent on neck in scalaris), (2) the stripes on back obscure, so that the pale spotting was most prominent (striping as prominent as spotting on back in scalaris), and (3) smudges of dark pigment on the lateralmost row of ventrals (scales whitish in scalaris). In regard to the last-mentioned character, only one of nine scalaris (RWA 1080) resembled exsanguis. Duellman and Zweifel (op. cit.:198) reported an average of 86.5 (82-92) granules at midbody for six specimens of scalaris from Cd. Chihuahua-a number which corresponds to an average of 89.3 (78-99) for seven of our nine scalaris. However, the remaining two scalaris (RGW 2752, RWA 1080) had low counts of 70 and 72, which correspond to those of our exsanguis, averaging 73.0 (72-75). The above-mentioned facts suggest the possibility of gene exchange (perhaps via male scalaris, as no male exsanguis are known) between these two species which we found to overlap approximately 33 airline miles. No differences in habitat preference between the two species were noted. Lizards of both species were collected between elevations of 5000 and 5300 feet in hilly to low mountainous terrain, usually on alluvial outwash fans, but several specimens were collected on steep, talus and boulder-strewn slopes. Vegetative cover was widely spaced and principally mesquite, several species of acacia, creosote bush, and patches of grasses and herbs. Motts of scrub oak occurred only at the locality of highest elevation north of Cd. Chihuahua. Bufo punctatus, Holbrookia texana, Phry-