Browsing by Author "Taylor, Harry Leonard."
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Item Comparative meristic variability in whiptail lizards (Teiidae, Aspidoscelis) : samples of parthenogenetic A. tesselata versus samples of sexually reproducing A. sexlineata, A. marmorata, and A. gularis septemvittata. (American Museum novitates, no. 3744)(American Museum of Natural History., 2012-05-23) Taylor, Harry Leonard.; Cole, Charles J.; Manning, Glenn J.; Cordes, James E.; Walker, James M. (James Martin)Is it correct, as is often assumed, that the clonal form of inheritance in parthenogenetic lizards results in less variability than occurs with genetic recombination in their sexually reproducing (gonochoristic) relatives? We tested this hypothesis by comparing morphological variability in samples of parthenogenetic Aspidoscelis tesselata and several gonochoristic species of whiptail lizards. To control for environmental factors that might differentially affect embryonic development of morphological characters, we compared samples obtained from the same or geographically adjacent localities. In addition, we compared apparently "uniclonal" and multiclonal samples from each of two color-pattern classes (C and E) of A. tesselata. For univariate meristic characters, parthenogenetic A. tesselata matched the variability of a sympatric gonochoristic species in 11 of 20 comparisons, had lower variability in six comparisons, and was more variable in three. For multivariate characters derived from principal components analyses (PCA), the relative meristic variability of samples of A. tesselata could not be predicted by its reproductive mode, color-pattern class, apparent "uniclonal" or multiclonal state, or geographic location. In addition, we compared A. tesselata, A. sexlineata, A. marmorata, and A. gularis septemvittata in a single PCA, with the latter two species representing the two ancestral taxa from which A. tesselata was derived through hybridization. Once again, relative variability of A. tesselata was not always predictable based on its reproductive mode. It had greater variability than A. sexlineata, equivalent variability with A. gularis septemvittata, and less variability than A. marmorata.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 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 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 Morphological variation in a unisexual whiptail lizard (Aspidoscelis exsanguis) and one of its bisexual parental species (Aspidoscelis inornata) (Reptilia, Squamata, Teiidae) : is the clonal species less variable? (American Museum novitates, no. 3849)(American Museum of Natural History., 2016-02-04) Cole, Charles J.; Taylor, Harry Leonard.; Townsend, Carol R.Two clonal lineages, each comprising multiple generations of unisexual A. exsanguis, were produced in the laboratory from two lizards that were collected at the same locality in the field. Based on 10 meristic and four additional characters, we assessed morphological scores and relative variation as follows: (1) between the two laboratory lineages; (2) between these lineages pooled and samples of A. exsanguis and the bisexual (gonochoristic) A. inornata from the field; and (3) between field samples of the clonal lizards and A. inornata from a nearby locality. The two lineages differed significantly in the means and variances of two univariate characters and the two most informative multivariate characters. Contrary to expectations, the pooled sample of cloned laboratory lineages of A. exsanguis were as variable as the bisexual species in all 10 univariate characters and four important multivariate characters.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.