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"This is the first comprehensive treatment of the biology of the Monstersauria in nearly 50 years, during which time our knowledge has increased dramatically. It gives the reader an unprecedented opportunity to understand the evolution, ecology, and behavior of gila monsters and beaded lizards, as well as insights into folklore, venom, and threats to the existence of these fabled animals."--William Cooper, Indiana University-Purdue University at Fort Wayne "Beck is the foremost authority on these animals and has published extensively on them. He provides a highly readable and fascinating summary of their biology."--Jonathan Campbell, author of Venomous Reptiles of Latin America
Reproductive Biology and Phylogeny of Lizards and Tuatara is a remarkable compendium of chapters written by the world's leading experts from over four continents. The book begins with a chapter recounting historical discoveries in reproductive biology and a review of phylogenetics and up-to-date hypotheses concerning evolutionary relationships amon
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.
The definitive reference source covering the 123 species of amphibians and reptiles found in New Mexico, including over 130 color plates and 100 maps.
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.