James M. Walker

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

Abstract 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. tesselatus Nine 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. tesselatus The 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. tesselatus usually have oocytes in the ovary, complete and well-organized ovarian follicle walls, inconspicuous connective tissue and fewer vacuoles in the well-vascularized ovary, the distal oviduct with a thin mucosa, well-developed alveolar glands restricted to the middle oviduct, a proximal oviduct with a thick mucosa and well-developed folds, and small mesonephric tubules. Female hybrids have a poorly defined follicular epithelium with little vascularization in small ovaries, empty or fluid-filled follicles without oocytes, few or no cilia in the middle oviduct, and numerous abnormally large mesonephric tubules. There is no evidence that Cnemidophorus tesselatus × C. tigris marmoratus females can produce viable and fertile eggs. Although hybrid males are capable of producing sperm that appear normal and were present in the epididymides, the allotriploid chromosome complement reduces the chance that sperm would carry genetically balanced sets of information. Although the annual production of hybrids could affect the long-term success of this local population of C. tesselatus two lines of evidence indicate that hybridization is unlikely to result in its extirpation. First, the population of C. tigris marmoratus at Arroyo del Macho is tightly associated with a microhabitat dominated by creosote bush. Because creosote bush is distributed there in small, widely scattered patches, the density of C. tigris marmoratus is relatively low, and many individuals of C. tesselatus escape insemination. This was evident from an absence of sperm in the reproductive tracts of 11 individuals of C. tesselatus collected during the peak reproductive season (May and June) of three different years. Second, reproductively mature individuals of C. tesselatus are significantly larger than comparable females of C. tigris marmoratus This translates into larger clutches, with the mean clutch size of C. tesselatus being twice as large as that of C. tigris marmoratus The disparity in mean clutch size in conjunction with habitat constraints on C. tigris marmoratus probably explains why C. tesselatus outnumbers both C. tigris marmoratus and hybrids by a ratio of approximately 2:1 at the hybridization site. Although hybridization between C. tesselatus and C. tigris marmoratus appears to be an annual event at Arroyo del Macho, there is no evidence that a new triploid parthenogenetic species is resulting from this hybridization activity—all female hybrids examined were sterile. Nevertheless, the hybridization taking place at Arroyo del Macho is a remarkable natural experiment in progress, with either evolutionary alternative—speciation vs. destabilizing hybridization—adding to an understanding of the dynamics between parthenogenetic and bisexual species in sympatric associations.

Application of the Evolutionary Species Concept to Parthenogenetic Entities: Comparison of Postformational Divergence in Two Clones of Aspidoscelis tesselata and between Aspidoscelis cozumela and Aspidoscelis maslini (Squamata: Teiidae)

Abstract Sumner Lake State Park, De Baca County, New Mexico, is the only known locality where three pattern classes of diploid, parthenogenetic Aspidoscelis tesselata (Sumner C, Sumner D, and Sumner E) coexist in syntopy. Reciprocal skin transplants confirmed that the pronounced phenotypic differences between Sumner C and Sumner E represent postformational genetic changes rather than separate hybridization origins. Sumner D is meristically indistinguishable from Sumner C and is considered to be a recent mutational derivative of the latter. In contrast, Sumner E is distinctly different from Sumner C in multivariate meristic characters and several important life-history characteristics. Discordant patterns of phenotypic variation characterize many geographically disjunct groups of A. tesselata classified as pattern class E, thus defying a cohesive diagnosis. Therefore, based on the evolutionary species concept (ESC), we consider Sumner C and Sumner E to be divergent clonal groups in the same species. We contrast this example with a parthenogenetic complex on the Yucatán Peninsula in which formal recognition of Aspidoscelis maslini and Aspidoscelis cozumela can be accommodated under the ESC.

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

Abstract 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 A. neomexicana × A. sexlineata viridis from Conchas Lake. Of the 23 allozyme loci analyzed, 9 showed no allelic variation among the individuals of the parental taxa and the hybrid examined; however, 12 loci were particularly informative for identifying the hybrid and its parental species. For most of these loci, the suspected hybrid (based on morphology and triploid karyotype) had electrophoretic banding patterns consistent with a triploid bearing a combination of alleles that included the two found in diploid A. neomexicana plus a third allele from the local A. sexlineata viridis. This is consistent with a cloned A. neomexicana ovum having been fertilized by a haploid A. sexlineata viridis spermatozoan. We present the first evidence of perennial hybridization in Aspidoscelis between a parthenogen and a species other than a progenitor. However, we found no evidence that occasional hybridization between A. neomexicana and A. sexlineata viridis has had a significant negative effect on either of these species at Conchas Lake.

Skin Histocompatibility between Syntopic Pattern Classes C and D of Parthenogenetic Cnemidophorus tesselatus in New Mexico

Abstract At Conchas Lake State Park, San Miguel County, New Mexico, four allozymic variants of parthenogenetic Cnemidophorus tesselatus pattern class C and three allozymic variants of C. tesselatus D are syntopic with one gonochoristic and two parthenogenetic congeners. Our study of 14 individuals revealed that C. tesselatus C and D from this site are histoincompatible with both their maternal, Cnemidophorus tigris marmoratus, and paternal, Cnemidophorus gularis septemvittatus, progenitors. Evidence of skin histocompatibility between these combinations of C. tesselatus pattern class C and D lizards supports the hypothesis of a single hybrid origin for representatives of this species at the study site.

Males of three normally parthenogenetic species of teiid lizards (Genus Cnemidophorus)

CAGLE, F. R. 1948. Observations on a population of the salamander Amphiuma tridactylum (Cuvier). Ecology 29:479-491. 1954. Observations on the life history of the salamander Necturus louisianensis. Copeia 1954(4):257-260. DUFFY, McF. 1961. Cold dogs. La. Conserv. 13(1):5-6, 21. GUNNING, G. E. 1963. The concepts of home range and homing in stream fishes. Ergeb. Biol. 26:202-215. AND C. R. SHOOP. 1963. Occupancy of home range by longear sunfish, Lepomis m. megalotis (Rafinesque), and bluegill, Lepomis m. macrochirus Rafinesque. Anim. Behav. 11: 325-330. NEILL, W. T. 1941. A collection of salamanders from Georgia. Copeia 1941(3):177. .1963. Notes on the Alabama waterdog, Necturus alabamensis Viosca. Herpetologica 19:166-174. PENN, G. H. 1959. An illustrated key to the crawfishes of Louisiana with a summary of their distribution within the state. Tulane Stud. Zool. 7:3-20. SHOOP, C. R. 1965. Aspects of reproduction in Louisiana Necturus populations. Am. Midi. Nat. 74:357-367. VIOSCA, P., JR. 1937. A tentative revision of the genus Necturus with descriptions of three new species from the southern Gulf drainage area. Copeia 1937(2):120-138.

Evolutionary and Systematic Implications of Skin Histocompatibility Among Parthenogenetic Teiid Lizards: Three Color Pattern Classes of Aspidoscelis dixoni and One of Aspidoscelis tesselata

Abstract The whiptail lizard Aspidoscelis dixoni (Teiidae) comprises three distinctive color pattern classes (i.e., variants); A and B are restricted to Presidio County, Texas, and C is isolated over 500 km to the west-northwest in Hidalgo County, New Mexico. Pattern class E of A. tesselata is widely distributed in Chihuahua, Texas, and New Mexico. Genetic data have verified that these parthenogenetic species are hybrid-derivatives of A. tigris marmorata ♀ X A. gularis septemvittata ♂; however, the number of hybridization events involved in their origin has remained problematic. We used 19 lizards in laboratory skin-grafting experiments to test the histoincompatibility responses among A. dixoni A, B, C, and A. tesselata E. The results of these graft exchanges indicated that individuals of all four pattern classes were mutually histocompatible to skin grafts, a level of genetic homogeneity indicative of the origin of A. dixoni and A. tesselata from the same hybrid lizard. Thus, the color pattern variants A. dixoni A, B, C, and A. tesselata E are identifiable products of mutation and/or recombination in a single historical group. Such postformational genetic changes have not been shown to be capable of mimicking the mutual graft rejection responses that occur between all members of historical groups derived from different hybrid zygotes. Falsification of the hypothesis that A. dixoni and A. tesselata were derived from different hybrid individuals also nullified the generally accepted rationale for their treatment as separate species. Aspidoscelis dixoni is revealed to consist of a morphologically well-defined grouping of three of the several diploid color pattern classes (i.e., tokogenetic arrays) in the A. tesselata complex that are also potentially diagnosable as species using similar criteria. Based on histocompatibility data presented herein for the A. tesselata complex and a review of preexisting data for other taxa, we provide a comparison of published opinions pertaining to the taxonomic status of A. dixoni and A. tesselata and the other named parthenogenetic entities in the A. cozumela, A. sexlineata, and A. tesselata species groups of Aspidoscelis. This generic name was recently resurrected from the synonymy of Cnemidophorus; however, monophyly has yet to be achieved for the revised genus “Cnemidophorus” owing to paraphyly in the “C. lemniscatus” species group. La lagartija cola de látigo Aspidoscelis dixoni (Teiidae) comprende tres clases distintivas de patrones de coloración (esto es, variantes); las clases A y B están restringidas al condado de Presidio, Texas, y la C está aislada a más de 500 km hacia el oeste-noroeste en el condado de Hidalgo, Nuevo Mexico. La clase E de A. tesselata está ampliamente distribuida en Chihuahua, Texas y Nuevo Mexico. Datos genéticos han verificado que estas especies partenogenéticas son derivadas de híbridos de ♀ de A. tigris marmorata y ♂ de A. gularis septemvittata; sin embargo, el número de eventos de hibridación que dio lugar a su origen ha permanecido incierto. Utilizamos 19 lagartijas en laboratorio para experimentos de injertos de piel para probar las respuestas de incompatibilidad de tejidos entre las clases A, B, y C de A. dixoni, y E de A. tesselata. Los resultados de estos intercambios de injertos indicaron que los individuos de las cuatro clases de patrones fueron histológicamente compatibles a los injertos de piel, un nivel de homogeneidad genética indicadora del origen de A. dixoni y A. tesselata de la misma lagartija híbrida. Por lo que, las variantes en el patrón de coloración A, B, C de A. dixoni, y E de A. tesselata son productos identificables de mutación y/o recombinación en un solo grupo histórico. Tales cambios genéticos postformativos no han mostrado ser capaces de imitar las respuestas de rechazo mutuo de los injertos que ocurren entre los miembros de grupos históricos derivados de diferentes cigotos híbridos. El rechazo de la hipótesis que A. dixoni y A. tesselata fueron derivados de diferentes individuos híbridos también nulifica el razonamiento generalmente aceptado de considerar a estas como especies separadas. Se revela que Aspidoscelis dixoni está compuesta de un grupo morfológico bien definido de tres de las varias clases de patrones de coloración diploides (esto es, arreglo tokogenético) en el complejo A. tesselata que son también potencialmente diagnosticadas como especies utilizando criterios similares. Basados sobre datos de compatibilidad histológica presentados aquí para el complejo A. tesselata, y sobre una revisión de datos preexistentes para otros taxa, proporcionamos una comparación de opiniones publicadas sobre el estatus taxonómico de A. dixoni y A. tesselata y las otras entidades partenogenéticas nombras en los grupos de especies A. cozumela, A. sexlineata, y A. tesselata del género Aspidoscelis. El nombre genérico fue recientemente resucitado de la sinonimia de Cnemidophorus; sin embargo, la monofilia aún tiene que probarse para el género “Cnemidophorus” debido a la parafilia restante en el grupo de especies “C. lemniscatus.”

Hybrid Cnemidophorus (Sauria: Teiidae) in Ninemile Valley of the Purgatoire River, Colorado

Canonical variate analysis (CVA) of color pattern and scutellation characters in lizards collected in Ninemile Valley of the Purgatoire River at Higbee, Otero Co., Colorado graphically depicted two forms of parthenogenetic Cnemidophorus tesselatus (diploid color pattern class C and triploid color pattern class B), gonochoristic C. sexlineatus, and hybrid C. tesselatus x C. sexlineatus as four morphologically distinctive groups. A newly obtained male specimen with a C. tesselatus-like color pattern entered as an unknown was classified to the hybrid group in the CVA. It represented the fourth tetraploid hybrid C. tesselatus B(3n) x C. sexlineatus collected in the valley. A female specimen was also classified to the hybrid group by the CVA. A triploid karyotype (3n = 69) and color pattern identified this female as a putative C. tesselatus C(2n) x C. sexlineatus hybrid. Whereas male hybrids are presumably sterile and biological novelties at most, the possibility remains that a female hybrid could be the founder of a new parthenogenetic lineage. Zweifel (1965) informally described six color pattern classes of parthenogenetic lizards (A, B, C, D, E, F) in the Cnemidophorus tesselatus complex (family Teiidae) of which four (A-D) were reported from Colorado. Wright and Lowe (1967a) found that pattern classes A and B were triploid hybrid derivatives and pattern classes CF were diploid hybrid derivatives. Analyses of morphology (Walker et al., 1990) and karyology (Cordes, 1991) identified three of Zweifels pattern classes of C. tesselatus in sympatry in Ninemile Valley of the Purgatoire River at Higbee, Otero Co., Colorado rather than two as indicated by Zweifel (1965), Densmore et al. (1989), and Wright (1993). These included diploid C. tesselatus C and D and triploid B, not triploid pattern class C as indicated by Parker and Selander (1976), Densmore et al. (1989), Wright (1993), and Leuck (1993). We found that the Ninemile Valley triploid population was morphologically indistinguishable from the pattern class B population described by Zweifel (1965) from Pueblo Co., Colorado. In samples collected in the valley since 1960 by various workers, diploid C. tesselatus outnumbered triploid C. tesselatus by a combined ratio of over 7:1. Moderate numbers of the gonochoristic species C. sexlineatus, the paternal parent of triploid C. tesselatus B (Wright and Lowe, 1967a; Parker and Selander, 1976), were also found in many parts of the area sampled. Four hybrid male C. tesselatus x C. sexlineatus were included in these collections. Three of these were described, and their probable parental forms identified as triploid C. tesselatus B x C. sexlineatus, by Walker et al. (1990). In the present study we describe the most recently collected hybrid male Cnemidophorus, infer its putative parentage on the basis of critical morphological characters, and evaluate the possibility of a hybrid origin for a female specimen displaying an ambiguous combination of classification characters. MATERIALS AND METHODS-Characters of scutellation that were quantitatively analyzed included: number of granules around midbody (GAB), number of granules from occiput to rump (OR), sum of left and right femoral pores (FP), number of subdigital lamellae on the longest toe of the left pes (SDL), sum of left and right circumorbital scales (COS), sum of This content downloaded from 207.46.13.57 on Mon, 08 Aug 2016 05:24:23 UTC All use subject to http://about.jstor.org/terms 236 The Southwestern Naturalist vol. 39, no. 3

PARTHENOGENETIC CNEMIDOPHORUS TESSELATUS COMPLEX AT HIGBEE, COLORADO : RESOLUTION OF 30 YEARS OF CONTROVERSY

At times over 30 years, various authors have expressed conflicting opinions on the composition of the parthenogenetic Cnemidophorus tesselatus complex at Higbee, Otero County, Colorado, the only known site of sympatry between diploid and triploid members of this complex. Recently, some workers have stated that two rather than three distinctive parthenogens occur at Higbee, one being an undescribed triploid species (tentatively designated pattern class C), which resulted from hybridization between C. tesselatus D(2n) and gonochoristic C. sexlineatus. Alternatively, our study identified two diploid pattern classes [C(2n) and D(2n)] and one triploid pattern class [B(3n)] among specimens of C. tesselatus from Higbee (including those with electrophoretically determined ploidy levels). We used two canonical variate analyses (CVA) to test hypotheses concerning the identity and origin of the triploid form. CVA1 suggested that specimens of the Higbee triploid form represented C. tesselatus B(3n), not an undescribed species. CVA2 suggested that C. tesselatus B(3n) was derived from a C. tesselatus C(2n) x C. sexlineatus hybrid, not a hybrid involving C. tesselatus D(2n).

Reproductive Characteristics and Body Size in the Parthenogenetic Teiid Lizard Cnemidophorus tesselatus: Comparison of Sympatric Color Pattern Classes C and E in De Baca County, New Mexico

Cnemidophorus tesselatus is an allodiploid, parthenogenetic lizard comprised of a number of distinctive tokogenetic arrays (Frost and Hillis, 1990) presently identified by four color pattern class descriptors: C, Colorado D, New Mexico D, and E (Taylor et al., 1996; Walker et al., 1997). The macrogeographic relationships of these pattern classes were outlined in Zweifels (1965) pioneering study of geographic variation in Cnemidophorus tesselatus. Pattern class C was known to exist isolated from the other pattern classes in parts of southeastern Colorado, northwestern Oklahoma, and northwestern Texas. Sympatry between pattern classes C and D was known to occur only in the vicinities of the historic townsite of Higbee, Otero County, Colorado, and Conchas Lake, San Miguel County, New Mexico. Pattern class E occurred to the south, with specimens from Fort Sumner, De Baca County, New Mexico, approximately 105 km south of the Conchas Lake locality, documenting the closest proximity of pattern class E to pattern classes C and D.

Allocation of Populations of Whiptail Lizards to septemvittatus Cope, 1892 (Genus Cnemidophorus) in Chihuahua, México, and the scalaris Problem

Abstract We used 11 samples comprising 224 specimens collected between 1966 and 1999 in Chihuahua, México, and Texas to clarify aspects of color pattern and meristic variation in the notoriously difficult gonochoristic Cnemidophorus gularis-scalaris-septemvittatus complex which is characterized by enlarged mesoptychial scales and enlarged and platelike postantebrachial scales. We allocated populations represented in all SEPT-CMX samples except SEPT-CMX5 from northeastern Chihuahua to Cnemidophorus gularis septemvittatus Cope, 1892, type locality Marfa, Presidio County, Texas, represented by sample SEPT-TUS1. This allocation adds 28 newly discovered sites in Chihuahua to the single valid record previously known for the taxon in that state. Our study revealed that three taxonomically distinct forms, one in Trans-Pecos Texas east of Alamito Creek, Presidio County, and another in southern Coahuila, México (both beyond the scope of this study), were included in septemvittatus in a 1962 taxonomic revision. Clarification of the distribution and variation of C. g. septemvittatus in Chihuahua sets the stage for further systematic studies. Whiptail lizards in our SCAL-CMX samples from Chihuahua, for which only the name Cnemidophorus gularis scalaris Cope, 1892, is available, represent two forms distinguishable from each other and from C. g. septemvittatus on the basis of color patterns that remain distinct through ontogeny. Further sampling of Cnemidophorus populations in Chihuahua will be required to fully resolve the scalaris problem.