Details - 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

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

Title

By

Taylor, Harry Leonard.
Cole, Charles J.
Dessauer, Herbert C.
Parker, E. D., Jr.

Type

Book

Material

Published material

Publication info

New York, NY, American Museum of Natural History, c2003

Notes

Caption title.

"December 9, 2003."

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 5 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 Maslin's (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 2100/296, 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.