Morphological Divergence and Genetic Variation in the Triploid Parthenogenetic Teiid Lizard, Aspidoscelis neotesselata
The parthenogenetic triploid lizard Aspidoscelis neotesselata originated from a hybridization event between a female of diploid parthenogenetic Aspidoscelis tesselata (pattern class C) and a male of Aspidoscelis sexlineata viridis, and A. neotesselata is morphologically more similar to its maternal progenitor, A. tesselata. The geographic distribution of A. neotesselata is characterized by localized arrays of individuals located within a four-county area in southeastern Colorado, and postorigin divergence is visually evident in its four allopatric color pattern classes (A, B, C, and D). A fundamental pattern of morphological divergence was revealed by a multivariate partitioning of its four color pattern classes into two basic groups: an A group (pattern classes A and D) and a B group (pattern classes B and C). A problem introduced by this grouping is the incongruence between the multivariate similarity of pattern classes A and D and the closer geographic proximity of other color pattern classes to each of A and D. All four color-pattern classes of A. neotesselata had a modified triploid karyotype of 69 + 1 chromosomes (3n = 70). Electrophoretic assessment of 31 nuclear gene loci across the four color-pattern classes revealed postorigin genetic variation only at the mannose-6-phosphate isomerase (MPI) locus, but A. neotesselata had a remarkable heterozygosity of 71% based on these loci.Abstract
Representatives of the progenitor species of parthenogenetic Aspidoscelis neotesselata from Otero County, southeastern Colorado: (A) Aspidoscelis sexlineata viridis: HLT 0334, 71-mm SVL. (B) Aspidoscelis tesselata C: HLT 0125, 79-mm SVL (size at which reproductive maturity can be attained in southeastern Colorado; Taylor et al., 1999). (C) Aspidoscelis tesselata C: HLT 0172, 104-mm SVL (near-maximum size for this species). See Appendix 1 for specific localities.
Representatives of four color-pattern classes of Aspidoscelis neotesselata from southeastern Colorado. (A) Pattern class B (group B1): HLT 0118, 96-mm SVL; Otero County, Nine-Mile Valley. (B) Pattern class C (group C): HLT 0212, 105-mm SVL; Pueblo County, historic town site of Lime near St. Charles River. (C) Pattern class A (group A2): HLT 0095, 95-mm SVL; Fremont County, Indian Springs Ranch. (D) Pattern class D (group D): HLT 0337, 93-mm SVL; Otero County, city of La Junta. See Appendix 1 for specific localities.
Relative locations in southeastern Colorado of sampling localities of pattern classes A, B, C, and D of Aspidoscelis neotesselata analyzed in this study. Designations A1, A2, B1, B2, C, and D refer to disjunct arrays designated by pattern class and locality. Specific locations of collecting sites are provided in Appendix 1. This figure was modified from an image provided by Google Earth©.
Scatter plots of multivariate scores from (A) principal-components analysis and (B) canonical variate analysis of Aspidoscelis neotesselata (N = 316) and samples of its progenitor species, Aspidoscelis tesselata C (N = 76) and Aspidoscelis sexlineata viridis (N = 35), from southeastern Colorado. Ellipses define 95% confidence limits of group variation; axis percentages are proportions of the variation accounted for by principal components (PC1 and PC2) and canonical variates (CV1 and CV2).
Scatter plots of multivariate scores from (A) principal components analysis and (B) canonical variate analysis of 318 individuals in six groups of Aspidoscelis neotesselata (defined by color pattern class and geographic locality) from southeastern Colorado. Ellipses define 95% confidence limits of group variation; axis percentages are proportions of the variation accounted for by principal components (PC1 and PC2) and canonical variates (CV1 and CV2).
Two basic morphological groups of Aspidoscelis neotesselata: (1) B1, B2, and C; and (2) A1, A2, and D, as shown by the separation of two clusters of centroids. Group centroids (points created at the intersections of means for CV1 and CV2) are shown as solid circles and depict positions in two dimensions. Aspidoscelis tesselata C was included in the analysis to maximize separation of groups of A. neotesselata on CV2.
Electrophoretic phenotypes of six proteins (Table 9) as expressed on separate gels, each with lanes representing six lizards (genotypes in parentheses). PEPA, a dimeric enzyme, which is triallelic in Aspidoscelis neotesselata and has the a-allele from Aspidoscelis sexlineata viridis. MPI, monomeric, showing all known clonal variants in A. neotesselata and two in Aspidoscelis tesselata. sACOH, monomeric, showing clonal variants in A. tesselata. TF, monomeric, showing the a-allele in A. neotesselata, inherited from A. sexlineata viridis. LDH1, tetrameric, showing dosage effects of two b-alleles and one a-allele in A. neotesselata. GPI, dimeric, showing dosage effects of two c-alleles and one a-allele in A. neotesselata. Abbreviations are as follows: NEO, A. neotesselata, with pattern class specified by letter; SEX, A. sexlineata viridis; TES, A. tesselata, with pattern class specified by letters. For each, the anode is to the right. Specimens examined for the lanes labeled TES E were listed as individuals of TES E-C in Taylor et al. (2003). The specimen examined for the lane labeled as SEX was listed in Manning et al. (2005).
Triploid karyotype of Aspidoscelis neotesselata, with 70 chromosomes that were combined through two steps of hybridization that involved three, bisexual ancestral species. Chromosomes are arranged to represent the haploid complements inherited from each ancestor, as follows: top two rows, Aspidoscelis tigris marmorata (note fission of the X-chromosome (third largest; uppermost arrow), resulting in 24 chromosomes instead of 23); middle two rows, Aspidoscelis gularis septemvittata, with 23 chromosomes; bottom two rows, Aspidoscelis sexlineata viridis, with 23 chromosomes. Note the secondary constrictions (=NORs; Ward and Cole, 1986) present in both the middle and bottom genomes (lower arrows). The upper four rows represent the karyotype of A. tesselata, resulting from the first ancestral step of hybridization; the lowermost genome was added in the second step. The specimen (UAZ 18527) is of pattern class A, but all specimens of all pattern classes examined had the same karyotype. Bar represents 10 microns.
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