Hybridization in lizards

56 p. : ill. (some col.), map ; 26 cm.Includes bibliographical references (p. 51-53).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