Charles J. Cole

Phylogenetic Relationships of Whiptail Lizards of the Genus Cnemidophorus (Squamata: Teiidae): A Test of Monophyly, Reevaluation of Karyotypic Evolution, and Review of Hybrid Origins

Abstract 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 others 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.

Hybridization between multiple fence lizard lineages in an ecotone: locally discordant variation in mitochondrial DNA, chromosomes, and morphology

We investigated a hybrid zone between two major lineages of fence lizards (Sceloporus cowlesi and Sceloporus tristichus) in the Sceloporus undulatus species complex in eastern Arizona. This zone occurs in an ecotone between Great Basin Grassland and Conifer Woodland habitats. We analysed spatial variation in mtDNA (N = 401; 969 bp), chromosomes (N = 217), and morphology (N = 312; 11 characters) to characterize the hybrid zone and assess species limits. A fine‐scale population level phylogenetic analysis refined the boundaries between these species and indicated that four nonsister mtDNA clades (three belonging to S. tristichus and one to S. cowlesi) are sympatric at the centre of the zone. Estimates of cytonuclear disequilibria in the population closest to the centre of the hybrid zone suggest that the S. tristichus clades are randomly mating, but that the S. cowlesi haplotype has a significant nonrandom association with nuclear alleles. Maximum‐likelihood cline‐fitting analyses suggest that the karyotype, morphology, and dorsal colour pattern clines are all coincident, but the mtDNA cline is skewed significantly to the south. A temporal comparison of cline centres utilizing karyotype data collected in the early 1970s and in 2002 suggests that the cline may have shifted by approximately 1.5 km to the north over a 30‐year period. The recent northward expansion of juniper trees into the Little Colorado River Basin resulting from intense cattle overgrazing provides a plausible mechanism for a shifting hybrid zone and the introgression of the mtDNA haplotypes, which appear to be selectively neutral. It is clear that complex interactions are operating simultaneously in this contact zone, including the formation of hybrids between populations within S. tristichus having diagnostic mtDNA, morphology, karyotypes, and dorsal colour patterns, and secondary contact between these and a distantly related yet morphologically cryptic mtDNA lineage (S. cowlesi).

Influence of gene dosage on electrophoretic phenotypes of proteins from lizards of the genus Cnemidophorus

Abstract 1. 1. Electrophoretic phenotypes of 23 proteins representing 29 loci indicate that populations of the diploid bisexual species of whiptail lizards normally have heterozygosity indices of about 0.05. 2. 2. Comparison of the same proteins of diploid and triploid parthenogenetic (unisexual) species of whiptail lizards reveals very high and fixed heterozygosities (0.41 and 0.45). 3. 3. Banding patterns of isozymes at loci that are heterozygous in the unisexual forms and in a triploid and a tetraploid hybrid between unisexual and bisexual species indicate that the alleles involved are all equally functional within individual cells. 4. 4. Proteins of these diploid, triploid and tetraploid lizards have the same number of polypeptide chains/molecule as do other vertebrates for which relevant data exist. 5. 5. Ploidy of specimens whose karyotypes are unknown can be estimated with reasonable confidence by careful electrophoretic analysis of a variety of proteins.

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.

HYBRIDIZATION AMONG WESTERN WHIPTAIL LIZARDS (CNEMIDOPHORUS TIGRIS) IN SOUTHWESTERN NEW MEXICO:POPULATION GENETICS, MORPHOLOGY, AND ECOLOGY INTHREE CONTACT ZONES

Abstract 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.

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

Abstract Aspidoscelis tesselata exhibits significant clonal diversity despite its recent origin (from hybridization between A. tigris marmorata and A. gularis septemvittata) and its parthenogenetic mode of reproduction. Two hypotheses have been advanced to explain the derivation of its genetic and morphological variation: (1) separate parthenogenetic lineages derived from several different F1 hybrid zygotes, and (2) postformational mutations occurring in a parthenogenetic lineage derived from a single F1 hybrid zygote. We evaluated these competing hypotheses with evidence from skin transplant studies, protein electrophoresis, multivariate analyses of morphological characters, and geographic distributions of pertinent groups. Starting with the clonal diversity at Conchas Lake State Park, San Miguel County, New Mexico, we expanded the study to include populations at Sumner Lake State Park and Fort Sumner (De Baca County), Puerto de Luna (Guadalupe County), and Arroyo del Macho and Roswell (Chaves County). This enabled us to resolve origins of color pattern classes and genotypic clones in eastern New Mexico. We used pattern class designations C-E and E-C to signify that elements of both pattern classes were expressed in populations at Conchas Lake and Arroyo del Macho. The two pattern classes at Conchas Lake (C-E and D) had the same F1 hybrid karyotype (2n = 46), with haploid sets of 23 chromosomes characteristic of each progenitor species of A. tesselata. Clonal variation was found at 4 of the 35 gene loci examined electrophoretically: GPI (glucose-6-phosphate isomerase), EST2 (a muscle esterase), sACOH (aconitase hydratase), and MPI (mannose-6-phosphate isomerase). The strong congruence between genotype and morphological variation facilitated the characterization of three morphological subgroups of C-E. Although these subgroups lacked individually distinctive color patterns, they were discriminated effectively in canonical variate analyses based on scalation characters and a priori groups of known genotype. Nine individuals of Conchas C-E and four individuals of Conchas D have histocompatibility data from a recent skin transplant study (Cordes and Walker, 2003). The subgroup identities of the C-E specimens document histocompatibility among the three morphological subgroups of C-E and between each subgroup and representatives of pattern class D. This evidence, together with Maslins (1967) report of histocompatibility between pattern classes C and E, suggests that all color pattern classes, morphological subgroups, and genotypic clones of A. tesselata can be traced back to a single ancestral F1 hybrid zygote. A pair of pale broken lines in the middorsal region distinguishes pattern class D from the other pattern classes. However, Conchas ID shared the GPI −100/−96, EST2 100/96 genotype with Conchas IC-E, and individuals of these pattern classes were very similar in multivariate meristic characters. Sumner D expressed the same type of relationship, resembling the syntopic population of Sumner C rather than the other population of D. In addition, certain individuals of Sumner C had partially divided (D-like) vertebral lines—additional evidence that Sumner C was ancestral to Sumner D. We conclude that pattern class New Mexico D is polyphyletic, having originated twice from different individuals of C-E and C in the vicinities of Conchas and Sumner Lakes. The northern position of pattern classes C and C-E in the range of A. tesselata is consistent with recent colonizations by individuals from more southerly populations. A candidate source population, based on its extensive color pattern and meristic variation, is E-C at Arroyo del Macho. The strong morphological resemblance of several northern populations to Macho E-C rather than to either syntopic clones or geographically proximate populations of other pattern classes supports this possibility. Evidence from geographic distributions, patterns of genotypic and meristic variation, and histocompatibility identifies postformational mutations as the likely basis for the genetic and morphological variation found in A. tesselata. This variation also includes different life-history characteristics between pattern classes C and E at Sumner Lake State Park. The name tesselata is presently associated indirectly with pattern class C through the neotype of A. tesselata. The neotype is a specimen of Colorado D, a derivative of pattern class C. With respect to pattern classes E-C, E, and other southern variants, taxonomic restructuring would confront mosaic patterns of genotypic, phenotypic, and geographic variation—patterns expected from random mutations in clonally reproducing species. Aspidoscelis tesselata has exploited a variety of ecological opportunities despite the constraints of clonal inheritance. Postformational mutations in the generalized genotype acquired from its progenitor species may have contributed to its ecological success.

Amphibians and reptiles of Guyana, South America: illustrated keys, annotated species accounts, and a biogeographic synopsis

Abstract Guyana has a very distinctive herpetofauna. In this first ever detailed modern accounting, based on voucher specimens, we document the presence of 324 species of amphibians and reptiles in the country; 148 amphibians, 176 reptiles. Of these, we present species accounts for 317 species and color photographs of about 62% (Plates 1–40). At the rate that new species are being described and distributional records are being found for the first time, we suspect that at least 350 species will be documented in a few decades. The diverse herpetofauna includes 137 species of frogs and toads, 11 caecilians, 4 crocodylians, 4 amphisbaenians, 56 lizards, 97 snakes, and 15 turtles. Endemic species, which occur nowhere else in the world, comprise 15% of the herpetofauna. Most of the endemics are amphibians, comprising 27% of the amphibian fauna. Type localities (where the type specimens or scientific name-bearers of species were found) are located within Guyana for 24% of the herpetofauna, or 36% of the amphibians. This diverse fauna results from the geographic position of Guyana on the Guiana Shield and the isolated highlands or tepuis of the eastern part of the Pantepui Region, which are surrounded by lowland rainforest and savannas. Consequently, there is a mixture of local endemic species and widespread species characteristic of Amazonia and the Guianan Region. Although the size of this volume may mislead some people into thinking that a lot is known about the fauna of Guyana, the work has just begun. Many of the species are known from fewer than five individuals in scientific collections; for many the life history, distribution, ecology, and behavior remain poorly known; few resources in the country are devoted to developing such knowledge; and as far as we are aware, no other group of animals in the fauna of Guyana has been summarized in a volume such as this to document the biological resources. We briefly discuss aspects of biogeography, as reflected in samples collected at seven lowland sites (in rainforest, savanna, and mixed habitats below 500 m elevation) and three isolated highland sites (in montane forest and evergreen high-tepui forest above 1400 m elevation). Comparisons of these sites are preliminary because sampling of the local faunas remains incomplete. Nevertheless, it is certain that areas of about 2.5 km2 of lowland rainforest can support more than 130 species of amphibians and reptiles (perhaps actually more than 150), while many fewer species (fewer than 30 documented so far) occur in a comparable area of isolated highlands, where low temperatures, frequent cloudiness, and poor soils are relatively unfavorable for amphibians and reptiles. Furthermore, insufficient study has been done in upland sites of intermediate elevations, where lowland and highland faunas overlap significantly, although considerable work is being accomplished in Kaieteur National Park by other investigators. Comparisons of the faunas of the lowland and isolated highland sites showed that very few species occur in common in both the lowlands and isolated highlands; that those few are widespread lowland species that tolerate highland environments; that many endemic species (mostly amphibians) occur in the isolated highlands of the Pakaraima Mountains; and that each of the isolated highlands, lowland savannas, and lowland rainforests at these 10 sites have distinctive faunal elements. No two sites were identical in species composition. Much more work is needed to compare a variety of sites, and especially to incorporate upland sites of intermediate elevations in such comparisons. Five species of sea turtles utilize the limited areas of Atlantic coastal beaches to the northwest of Georgetown. All of these are listed by the International Union for the Conservation of Nature as being of global concern for long-term survival, mostly owing to human predation. The categories of Critically Endangered or Endangered are applied to four of the local sea turtles (80%). It is important to protect the few good nesting beaches for the sea turtles of Guyana. We have documented each of the species now known to comprise the herpetofauna of Guyana by citing specimens that exist in scientific collections, many of which were collected and identified by us and colleagues, including students of the University of Guyana (UG). We also re-identified many old museum specimens collected by others in the past (e.g., collections of William Beebe) and we used documented publications and collection records of colleagues, most of whom have been working more recently. We present dichotomous keys for identifying representatives of the species known to occur in Guyana, and we present brief annotated species accounts. The accounts provide the current scientific name, original name (with citation of the original description, which we personally examined in the literature), some outdated names used in the recent past, type specimens, type localities, general geographic distribution, examples of voucher specimens from Guyana, coloration in life (and often a color photograph), and comments pointing out interesting subjects for future research.

PHYSIOLOGICAL VARIATION AND ALLOMETRY IN WESTERN WHIPTAIL LIZARDS (CNEMIDOPHORUS TIGRIS) FROM A TRANSECT ACROSS A PERSISTENT HYBRID ZONE

A hybrid zone involving Cnemidophorus tigris punctilinealis (formerly gracilis) and C. tigris marmoratus in southwestern New Mexico and adjacent Arizona is narrow and characterized by abrupt and concordant change in both morphological characters and allele frequencies studied by protein electrophoresis. We compared adult C. tigris sampled from three locations that span the hybrid zone. Body mass was positively associated with both treadmill endurance at 1.0 km/h and maximal sprint running speed on a high-speed treadmill, although the largest individuals were not the fastest sprinters. Males and females differed significantly for maximal sprint ruloning speed, liver mass, and kidney mass (ANCOVA with body mass as covariate). We found no statistically significant population differences for body mass, maximal sprint running speed, standard metabolic rate at 40C, blood hematocrit levels, or heart mass. Hybrids tended to have lower treadmill endurance rlnning capacities as compared with the pure forms, but the difference was not statistically significant. Cnemidophorus tigris punctilinealis and the hybrids both had significantly heavier kidneys, relative to body mass, than did C. tigris marmoratus. Hybrid individuals also had significantly heavier livers as compared with either pure population. However, the present data cannot rule out the possibility that the observed differences in organ masses were related to reproductive status as opposed to being genetically based population differences. Thus, our results do not suggest that hybrid individuals differ from nonhybrids with respect to Darwinian fitness.

Laboratory Hybridization Among North American Whiptail Lizards, Including Aspidoscelis Inornata Arizonae × A. tigris marmorata (Squamata: Teiidae), Ancestors of Unisexual Clones in Nature

ABSTRACT 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.

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.