Browsing by Author "Hardy, Laurence M."
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ItemKaryotypes of six species of colubrid snakes from the Western Hemisphere, and the 140-million-year-old ancestral karyotype of Serpentes. (American Museum novitates, no. 3926)(American Museum of Natural History., 2019-04-29) Cole, Charles J.; Hardy, Laurence M.Karyotypes are described for six species of snakes from the Western Hemisphere, and comparisons are made with all species of snakes from around the world that have been karyotyped with modern methods. Although there is significant karyotypic variation in snakes, there is one basic karyotype that is shared by members of all families of snakes, representing widely divergent lineages, extending from today back through the evolutionary history of the Serpentes. Long-term survival of the ancestral snake karyotype may be a result of canalization, similar to some ancient chromosomes of turtles. ItemLaboratory 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. ItemMorphology of a sterile, tetraploid, hybrid whiptail lizard (Squamata, Teiidae, Cnemidophorus). American Museum novitates ; no. 3228(New York, NY : American Museum of Natural History, 1998) Hardy, Laurence M.; Cole, Charles J."Experimental hybridization with whiptail lizards has been conducted in order to improve understanding of the evolution of parthenogenesis in vertebrates and the effects of horizontal gene transfer in Cnemidophorus, the systematics of which has been confused owing to the reticulate phylogeny within the genus. Here we describe the external morphology and reproductive tissue histology of a sterile tetraploid hybrid between C. sonorae (triploid, unisexual) X C. tigris (diploid, bisexual), and compare her to her parents and siblings that developed from unfertilized eggs (normally cloned C. sonorae). This may help to identify F³ hybrids that are found in nature and may help to determine whether they are sterile without conducting extensive laboratory breeding programs. Considering that the maternal parent (C. sonorae) represented a clone that was of hybrid origin itself, the four genomes in the tetraploid hybrid historically were derived from three hybridization events among three bisexual species of Cnemidophorus, probably as follows: [(inornatus [female] X burti [male]) X burti [male] ] X tigris [male]. The tetraploid inherited 100% of its mother's genes and morphologically was very similar to her and her cloned offspring, particularly in scalation. Nevertheless, it was slightly larger than its siblings at hatching, grew faster than its siblings, attained a larger size, and, beginning at an age of six months, developed dorsal spots reflecting paternal traits in its color pattern. However, if this lizard had been found in nature, without any knowledge of its life history and in the absence of genetic data, it could easily have been misidentified as Cnemidophorus exsanguis, which it resembled more closely than its parental species. Although she reached adult size and lived for more than two years beyond the age at which her cloned siblings produced offspring (nine months), the tetraploid never reproduced. Her ovaries were abnormally small, had poorly defined follicular epithelium with little vascularization, and had either empty or fluid-filled follicles devoid of oocytes. She also had numerous abnormally large mesonephric tubules and few or no cilia in the median oviduct. These traits should be examined in other specimens hypothesized to be sterile F³ hybrid females"--P. 2. ItemNatural 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. ItemSystematics of North American colubrid snakes related to Tantilla planiceps (Blainville). Bulletin of the AMNH ; v. 171, article 3(New York : American Museum of Natural History, 1981) Cole, Charles J.; Hardy, Laurence M."Examination of numerous characters (primarily of head coloration, hemipenes, scutellation, and size and proportions) of more than 750 specimens suggests that Tantilla planiceps, as recognized by Tanner (1966), actually represents four distinct species: Tantilla planiceps (Blainville, 1835), of southern California and Baja California; Tantilla yaquia Smith, 1942, of southeastern Arizona and northwestern Mexico; Tantilla atriceps (Günther, 1895), of southern Texas and northeastern Mexico; and Tantilla hobartsmithi Taylor, '1936' (1937), which is broadly distributed in the southwestern United States and northern Mexico and usually has been considered synonymous with T. atriceps. Synonymies, diagnoses, descriptions, illustrations, range maps, and ecological notes are presented for each of these species. Tantilla atriceps and T. hobartsmithi are sibling species with strikingly different hemipenes. They also are the only species of the complex for which sympatry (in Coahuila) has been documented. Future collecting may well demonstrate sympatry at the periphery of the ranges of T. planiceps and T. hobartsmithi and of T. yaquia and T. hobartsmithi. Analysis of variation indicates that some classical taxonomic characters used previously (e.g., number of ventral scales) are not particularly reliable for distinguishing among species of Tantilla. The best specific characters we found are in anatomy of the hemipenes. Variation in hemipenial features usually is correlated with variation in head coloration. Because T. atriceps and T. hobartsmithi are sibling species, now known to differ consistently only in hemipenial characters, and because they exhibit sympatry at the periphery of their ranges, specific identification of females is a problem that requires additional investigation. Once it appeared that male copulatory organs would provide important, diagnostic characters for the four species formerly assigned to T. planiceps, we examined hemipenes on as many specimens (258) as were reasonably available. These included pertinent type-specimens and outgroup comparisons with T. gracilis, T. nigriceps, and T. wilcoxi; hemipenes of these species are distinctive also, and examples of all are described and illustrated (excepting T. wilcoxi). One problem that remains under investigation is the specific relationship between T. atriceps and southern populations of T. nigriceps. No such problem exists between T. hobartsmithi and T. nigriceps, however, as they differ rather consistently in hemipenes and head coloration, and they are sympatric in the western part of the range of T. nigriceps. We also examined maxillary bones, sex ratio, and karyotypes (including that of T. coronata) in addition to the characters mentioned above. Most of these data are not taxonomically useful, due either to lack of significant variation or lack of comparative data from congeners. A preferred cladogram of phylogenetic relationships of T. wilcoxi, T. planiceps, T. yaquia, T. nigriceps, T. atriceps, T. hobartsmithi, and T. gracilis is presented, as is a key to all species of Tantilla known to occur in the western United States and northern Mexico. The most useful characters for distinguishing species of Tantilla, particularly in North America, appear to be in the hemipenes and head coloration. Hereafter, all taxonomic studies within Tantilla routinely should include examination of hemipenes of the specimens examined. When possible, males should be selected as type-specimens"--P. 203.