Browsing by Author "Dessauer, Herbert C."
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Item The blue and green whiptail lizards (Squamata, Teiidae, Cnemidophorus) of the Peninsula de Paraguana, Venezuela : systematics, ecology, descriptions of two new taxa, and relationships to whiptails of the Guianas. American Museum novitates ; no. 3207(New York, N.Y. : American Museum of Natural History, 1997) Markezich, Allan L.; Cole, Charles J.; Dessauer, Herbert C.Item Congruent patterns of genetic and morphological variation in the parthenogenetic lizard Aspidoscelis tesselata (Squamata, Teiidae) and the origins of color pattern classes and genotypic clones in eastern New Mexico. American Museum novitates ; no. 3424(New York, NY : American Museum of Natural History, 2003) Taylor, Harry Leonard.; Cole, Charles J.; Dessauer, Herbert C.; Parker, E. D., Jr.Item Hybrid origin of a unisexual species of whiptail lizard, Cnemidophorus neomexicanus, in western North America : new evidence and a review. American Museum novitates ; ; no. 2905.(New York, N.Y. : American Museum of Natural History, 1988) Cole, Charles J.; Dessauer, Herbert C.; Barrowclough, George F.Item Hybridization among western whiptail lizards (Cnemidophorus tigris) in southwestern New Mexico : population genetics, morphology, and ecology in three contact zones. Bulletin of the AMNH ; no. 246([New York] : American Museum of Natural History, 2000) Dessauer, Herbert C.; Cole, Charles J.; Townsend, Carol R.Cnemidophorus tigris punctilinealis of the Sonoran Desert and C. t. marmoratus of the Chihuahuan Desert contact each other and interbreed in the Animas Valley of southwestern New Mexico. More than 600 specimens have been examined from the contact region, and data on biochemical genetics (mitochondrial DNA haplotypes, protein electrophoresis of nuclear gene products), chromosomes, external morphology (coloration, size, scalation), reproduction, and fitness have been compared for three hybrid zones. Habitats in the contact region were mapped and photographed, and they are discussed in the context of vegetational changes during Pleistocene to Recent times, which affected the geographic distribution of these animals. Data from mitochondrial DNA, allele frequencies at four protein loci (of 36 analyzed), and body coloration demonstrate that the areas of contact have steep, concordant, and coincident step-clines in which most gene exchange occurs in hybrid zones that are 3.2-7.8 km wide. Analyses of allele frequencies, genotype frequencies, and fixation indices (including Hardy-Weinberg equilibrium, linkage equilibrium, and cytonuclear equilibrium) indicate a population structure determined primarily by random mating and an absence of selection against hybrids. Estimates of gene flow indicate that the clines resulted from neutral secondary contact initiated with the newest reconnection of the Sonoran and Chihuahuan deserts within the present interglacial episode, from 1000 to 5000 years ago. This timeframe is consistent with paleoecological data from packrat middens. Analyses of karyotypes, morphology, reproduction, and physiology also fail to detect differences in fitness among lizards with various genotypes. Although it is possible that there are fitness differences that are too small to be detected by the sample sizes we employed, the data indicate that reproductive success, fitness, and the dynamics of populations within the hybrid zones presently are no different from those in nonhybrid populations. Earlier data, which suggested that one of the step-clines was moving, are not supported. The clines are located in fragile semiarid habitats that are subject to desertification. Consequently, we present considerable data and dated photographs of habitats, precise locations of sampling sites, and local allele frequencies, so that future investigators can monitor changes in position, width, or dynamics of these hybrid zones. In addition, the population genetics data are discussed in the context of the following: (1) absence of rare, apparently novel alleles forming in the hybrid zones; (2) genetic comparisons with additional subspecies of C. tigris (C. t. aethiops and C. t. septentrionalis); and (3) interspecific hybridization between C. tigris and other whiptail lizards of either bisexual or unisexual (parthenogenetic, clonal) species. Cnemidophorus tigris is one of the ancestors of some of the parthenogens, which are of hybrid origin, and our interest in their evolutionary history fuels our efforts to improve understanding of hybridization among whiptail lizards.Item Hybridization between parthenogenetic lizards (Aspidoscelis neomexicana) and gonochoristic lizards (Aspidoscelis sexlineata viridis) in New Mexico : ecological, morphological, cytological, and molecular context. American Museum novitates ; no. 3492(New York, NY : American Museum of Natural History, 2005) Manning, Glenn J.; Cole, Charles J.; Dessauer, Herbert C.; Walker, James M. (James Martin)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 3 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 x 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 x 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 x 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 x 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 x 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.Item Hybridization between the endangered unisexual gray-checkered whiptail lizard (Aspidoscelis dixoni) and the bisexual western whiptail lizard (Aspidoscelis tigris) in southwestern New Mexico ; American Museum novitates, no. 3555(New York, NY : American Museum of Natural History, 2007) Cole, Charles J.; Painter, Charles W. (Charles Wilson), 1949-; Dessauer, Herbert C.; Taylor, Harry Leonard.Hybridization between the unisexual Aspidoscelis dixoni and the bisexual Aspidoscelis tigris punctilinealis in southwestern New Mexico is documented by observations and analyses of external morphology (coloration, size, scalation), chromosomes (karyotypes), nuclear gene products (allozymes), and mitochondrial DNA. The locality (Hidalgo County, Antelope Pass of the Peloncillo Mountains, centered at 10.5 km west of Animas), consisting of only a few square kilometers, is the only place where this particular unisexual clone of A. dixoni exists. Because of its extreme rarity in recent years, A. dixoni has been listed as an endangered species in New Mexico, and the status of its populations has received intense study. Today, the cause(s) of endangerment remains unknown, although we hypothesize that interspecific competition may be the problem. Aspidoscelis dixoni is a diploid unisexual species that normally reproduces by parthenogenetic cloning, as demonstrated here with genetic data from laboratory-reared lizards. However, fertilization of its eggs in Antelope Pass is possible if mating occurs with a male of the syntopic bisexual species A. tigris punctilinealis. The resulting hybrids closely resemble their maternal parent morphologically, but they are triploid and the females observed to date have been sterile. Aspidoscelis t. punctilinealis is a recent invader of southwestern New Mexico. It is the dominant species of whiptail lizard today in the low-elevation, semiarid habitat of creosote desertscrub in Antelope Pass. The present rarity of A. dixoni in Antelope Pass, in contrast to its abundance a few decades ago, may result from negative interactions with this dominant species, including asymmetrical destabilizing hybridization. Only a few other populations of A. dixoni are known to exist, each in a limited area in southwestern Texas, so there is a hiatus of nearly 500 km between the small and restricted populations in New Mexico and Texas. Comparative genetic data presented here indicate that although these populations are similar, the population in New Mexico represents a unique clone. It has three alleles at 3 nuclear gene loci (among 31 examined) that distinguish it from the Texan populations, and it lacks a microchromosome that occurs in Texan populations. In addition, in this paper we present new comparative genetic data confirming that the origin of A. dixoni itself was from a hybrid between an A. tigris marmorata [female] x A. gularis septemvittata [male], consistent with earlier studies.Item Hybridization between whiptail lizards in Texas : Aspidoscelis laredoensis and A. gularis, with notes on reproduction of a hybrid. (American Museum novitates, no. 3947)(American Museum of Natural History., 2020-03-06) Cole, Charles J.; Dessauer, Herbert C.; Paulissen, Mark A.; Walker, James M. (James Martin)Karyotypes and allozyme data for 32 genetic loci overwhelmingly support the conclusion that Aspidoscelis laredoensis is a diploid all-female species that had a hybrid origin between A. gularis x A. sexlineatus. Comparisons of allozymes in individuals representing three mother-to-daughter generations raised in the laboratory suggest that they reproduce by parthenogenetic cloning. In addition to two previously described morphotypes (pattern classes A and B) that occur in southern Texas, we report the existence of three all-female clonal lineages based on allozymes. Individuals of at least one of these lineages occasionally hybridize in nature with males of A. gularis, producing viable and healthy triploid offspring that can grow to adulthood, one of which herself produced an offspring in the laboratory and could have represented a new, clonal triploid species. The possibility exists that cloned offspring of triploid hybrids are present in South Texas and/or northern Mexico, awaiting discovery. These would represent a new species that would appear to be very similar to A. laredoensis.Item Kentropyx borckiana (Squamata, Teiidae) : a unisexual lizard of hybrid origin in the Guiana region, South America. American Museum novitates ; no. 3145(New York, N.Y. : American Museum of Natural History, 1995) Cole, Charles J.; Dessauer, Herbert C.; Townsend, Carol R.; Arnold, Margaret G."More than 100 females and yet no males of Kentropyx borckiana are known from northern South America and Barbados. Features of external morphology, karyotypes, and biochemical genetics (electrophoresis of proteins encoded by 45 presumptive gene loci) reveal that individuals of K. borckiana from Guyana represent a unisexual clone that originated from one or more parthenogenetic F1 hybrids between Kentropyx calcarata X Kentropyx striata, the other two species of this genus known previously from the Guiana Region. Comparisons include data for Kentropyx altamazonica also, including the first specimens known from Venezuela (Amazonas Territory). Although K. altamazonica and K. calcarata are morphologically similar, genetically they are quite distinct. Origin of the unisexual Kentropyx borckiana involved hybridization between both morphologically and ecologically distinct ancestral species, unlike several other unisexual lizards of Neotropica. For example, clones of the parthenogenetic Gymnophthalmus underwoodi, Cnemidophorus cryptus, and Cnemidophorus pseudolemniscatus originated in the Guiana Region from hybrids between morphologically and ecologically similar, yet genetically distinct, ancestral species"--P. 2.Item Laboratory hybridization among North American whiptail lizards, including Aspidoscelis inornata arizonae x A. tigris marmorata (Squamata, Teiidae), ancestors of unisexual clones in nature. (American Museum novitates, no. 3698)(American Museum of Natural History., 2010) Cole, Charles J.; Hardy, Laurence M.; Dessauer, Herbert C.; Taylor, Harry Leonard.; Townsend, Carol R.The natural origin of diploid parthenogenesis in whiptail lizards has been through interspecific hybridization. Genomes of the parthenogens indicate that they originated in one generation, as the lizards clone the F₁ hybrid state. In addition, hybridization between diploid parthenogens and males of bisexual species has resulted in triploid parthenogenetic clones in nature. Consequently, the genus Aspidoscelis contains numerous gonochoristic (= bisexual) species and numerous unisexual species whose closest relatives are bisexual, and from whom they originated through instantaneous sympatric speciation and an abrupt and dramatic switch in reproductive biology. In order to study this phenomenon more closely, with hopes (unfulfilled) to witness the origin of parthenogenetic cloning in one generation, we maintained whiptail lizards in captivity. For more than 29 years, we caged males of bisexual species with females of bisexual and of unisexual species in attempts to obtain laboratory hybrids. Hybrids were raised to adulthood to see whether they would reproduce, but none did. The hybrid status of suspected laboratory hybrids was confirmed by karyotypic, allozyme, and morphological analyses, and histological studies were made on reproductive tissues of the hybrids, which were apparently sterile. The present paper focuses on the laboratory hybrids of two bisexual species, A. inornata arizonae ([female]) x A. tigris marmorata ([male]). These three individuals from one clutch of eggs were the only hybrids between two bisexual species that we obtained. The hybrids had a karyotype, allozymes (21 loci tested), and external morphology that were similar to those of A. neomexicana, which is a diploid parthenogen that had a hybrid origin in nature that was the reciprocal cross: A. t. marmorata ([female]) x A. inornata ([male]). Histological study showed that the largest and oldest laboratory hybrid raised, which appeared to be a female with inherited X chromosome of A. t. marmorata, was an intersex with an enormous adrenal. The other hybrid that reached adult size, a male, was also apparently sterile. Later, we review and summarize the information on the other laboratory hybrids we obtained over the years. These include two different combinations of hybrids between a male of a bisexual species and females of unisexual species (one diploid, one triploid), producing triploid and tetraploid hybrids, respectively, as a haploid genome from the male was added to the cloned egg. Considering only those specimens whose hybrid status was confirmed with genetic analyses, a total of only five hybrids from three crosses were obtained over 29 years. The effort involved having a total of 74 males of four species caged with 156 females of nine species, where individuals were caged together for at least six months (or less, if mating behavior was observed). Despite our extensive efforts to provide for their comfort and best health and captive environment, the lizards at times experienced health problems such as metabolic bone disease and a Salmonella infection. These definitely had a negative effect on reproduction, the full extent of which is unknown. Nevertheless, we estimate that successful hybridization among whiptail lizards (i.e., which results in healthy offspring capable of reproduction) is much more rare than we previously thought, although, paradoxically, it is far more common among Aspidoscelis than among nearly all other genera of lizards in the world, with the possible exception of lacertids.Item Missing link found : the second ancestor of Gymnophthalmus underwoodi (Squamata, Teiidae), a South American unisexual lizard of hybrid origin. American Museum novitates ; no. 3055(New York, N.Y. : American Museum of Natural History, 1993) Cole, Charles J.; Dessauer, Herbert C.; Markezich, Allan L.Item Natural hybridization between the teiid lizards Cnemidophorus tesselatus (parthenogenetic) and C. tigris marmoratus (bisexual) : assessment of evolutionary alternatives. American Museum novitates ; no. 3345(New York, NY : American Museum of Natural History, 2001) Taylor, Harry Leonard.; Cole, Charles J.; Hardy, Laurence M.; Dessauer, Herbert C.; Townsend, Carol R.; Walker, James M. (James Martin); Cordes, James E.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 x 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 x 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.Item Phylogenetic relationships of whiptail lizards of the genus Cnemidophorus (Squamata, Teiidae) : a test of monophyly, reevaluation of karyotypic evolution, and review of hybrid origins. American Museum novitates ; no. 3365(New York, NY : American Museum of Natural History, 2002) Reeder, Tod.; Dessauer, Herbert C.; Cole, Charles J.Phylogenetic relationships of the whiptail lizards of the genus Cnemidophorus are inferred based on a combined analysis of mitochondrial DNA, morphology, and allozymes. Within the Teiini, Teius and Dicrodon are the most basal lineages, and these two taxa form a graded series leading to a cnemidophorine clade containing Ameiva, Cnemidophorus, and Kentropyx. Cnemidophorus monophyly is not supported, with members of the neotropical "C." lemniscatus species group (except "C." longicaudus) being more closely related to species in other neotropical cnemidophorine taxa (Ameiva and Kentropyx). Ameiva is also paraphyletic. The "Cnemidophorus" lemniscatus species group is also paraphyletic, with a "C." murinus + "C." lemniscatus complex clade being more closely related to Kentropyx than to "C." lacertoides, "C." longicaudus, and/or "C." ocellifer. Although the "C." lemniscatus species group is paraphyletic, the three remaining bisexual "Cnemidophorus" species groups (deppii, sexlineatus, and tigris species groups) are each monophyletic. Together, these three groups form a clade (= North American "Cnemidophorus" clade), with the deppii and tigris species groups being sister taxa. Within the "Cnemidophorus" deppii species group, the Baja California "C." hyperythrus is the sister species to a more exclusive mainland Mexico clade containing "C." deppii and "C." guttatus. Except for a "C." inornatus + "C." sexlineatus clade and a monophyletic "C." gularis complex, the inferred inter- and intraspecific relationships within the sexlineatus species group are weakly supported. In none of the inferred phylogenies are the "C." costatus populations ("C." c. costatus and "C." c. griseocephalus) represented as each other's closest relatives. Because of Cnemidophorus paraphyly, nomenclatural changes are recommended. Aspidoscelis Fitzinger, 1843, is resurrected for the North American "Cnemidophorus" clade containing the deppii, sexlineatus, and tigris species groups (and the unisexual taxa associated with them). Lizards of the genus Aspidoscelis differ from all other cnemidophorine lizards by the combined attributes of absence of basal tongue sheath, posterior portion of tongue clearly forked, smooth ventral scutes, eight rows of ventral scutes at midbody, absence of anal spurs in males, mesoptychial scales abruptly enlarged over scales of gular fold (more anterior mesoptychials becoming smaller), three parietal scales, and three or four supraocular scales on each side. Previous studies using morphology and allozymes have determined that the unisexual Kentropyx borckiana originated from a historical hybridization event between the bisexual species K. calcarata and K. striata. In this study mitochondrial DNA confirms K. striata as the maternal ancestor of K. borckiana. A review of our current knowledge of teioid unisexuals and their hybrid origins is provided. Also, a reevaluation of teiine chromosomal evolution is presented from a phylogenetic perspective. These reviews elucidate the paradox that the capability of instantly producing parthenogenetic clones through one generation of hybridization has existed for approximately 200 million years, yet the extant unisexual taxa are of very recent origins. Consequently, these lineages must be ephemeral compared to those of bisexual taxa.Item Unisexual and bisexual whiptail lizards of the Cnemidophorus lemniscatus complex (Squamata, Teiidae) of the Guiana Region, South America : with descriptions of new species. American Museum novitates ; no. 3081(New York, N.Y. : American Museum of Natural History, 1993) Cole, Charles J.; Dessauer, Herbert C.Item Unisexual lizards of the genus Gymnophthalmus (Reptilia, Teiidae) in the Neotropics : genetics, origin, and systematics. American Museum novitates ; no. 2994(New York, N.Y. : American Museum of Natural History, 1990) Cole, Charles J.; Dessauer, Herbert C.; Townsend, Carol R.; Arnold, Margaret G.