Origins and Evolution in the Aspidoscelis cozumela Complex of Parthenogenetic Teiid Lizards: Morphological and Karyotypic Evidence and Paradoxes
The Aspidoscelis cozumela complex of parthenogenetic lizards of the Yucatán Peninsula originated from hybridization between individuals of Aspidoscelis angusticeps (maternal) and Aspidoscelis deppii deppii (paternal) followed by postorigin clonal divergence. A previous report of histocompatibility between two members of the complex, Aspidoscelis maslini and Aspidoscelis cozumela, is reliable evidence that they share a single hybridization event. However, evidence from mitochondrial DNA and histoincompatibility has been used to conclude that another member of the complex, Aspidoscelis rodecki, originated from a separate hybridization event. Although future evidence might tip the balance in favor of a two-hybridization model, we provide examples where evidence from mtDNA and histoincompatibility probably led to incorrect predictions of the number of hybridization events in parthenogenetic Aspidoscelis. In this study, we compared correspondence between patterns of morphological and karyotypic divergence among A. cozumela, A. rodecki, and northern populations of A. maslini and progenitor species to two-hybridization and one-hybridization models. Although morphological and karyotypic patterns can be explained by either model, the most parsimonious alternative is a single hybridization event followed by postformational divergence. El complejo Aspidoscelis cozumela de lagartijas partenogenéticas de la Península de Yucatán se originó de la hibridación entre individuos de Aspidoscelis angusticeps (especie materna) y Aspidoscelis deppii deppii (especie paterna) seguida por una divergencia clonal postorigen. Un reporte previo de histocompatibilidad entre dos miembros de este complejo, Aspidoscelis maslini y Aspidoscelis cozumela, es una evidencia confiable de que ellos comparten un evento de hibridación único. Sin embargo, evidencia de ADN mitocondrial e histoincompatibilidad ha sido utilizada para concluir que otro miembro de este complejo, Aspidoscelis rodecki, se originó de un evento de hibridación separado. Aunque evidencias futuras podrían inclinar la balanza en favor de un modelo de dos-hibridaciones, proporcionamos ejemplos donde evidencias de ADN mitocondrial e histoincompatibilidad probablemente conducen a predicciones incorrectas del número de eventos de hibridación en Aspidoscelis partenogenéticos. En este estudio, comparamos correspondencia entre patrones de divergencia morfológica y cariotípica entre A. cozumela, A. rodecki, y poblaciones del norte de A. maslini y especies progenitoras de modelos de dos-hibridaciones y una-hibridación. Aunque patrones morfológicos y cariotípicos pueden ser explicados por cualquiera de estos dos modelos, la alternativa más parsimoniosa es un evento único de hibridación seguido de divergencia postformativa.Abstract
Resumen
Geographic relationships among samples examined: A. cozumela (C), A. maslini (M1, M2, and M3), A. rodecki (R), and representative progenitor populations: A. a. angusticeps (AA1, AA2, AA3, and AA4) and A. d. deppii (D1 and D2).
Representatives of the A. cozumela complex from sampling sites that include karyotyped individuals: (A) A. maslini: Guatemala, Petén, Ramate (UAZ 27479, snout–vent length (SVL) = 67 mm); (B) A. maslini: México, Campeche, Isla Carmen, 4 km SW Puerto Real (UAZ 29323, SVL = 69 mm); (C) A. cozumela: México, Quintana Roo, Isla Cozumel, Caleta (UAZ 29363, SVL = 69 mm); (D) A. rodecki: México, Quintana Roo, Isla Mujeres, airport (UAZ 29358, SVL = 53 mm). UAZ = University of Arizona Museum of Natural History (Herpetology), Department of Ecology and Evolutionary Biology, Tucson.
Morphological meristic variation expressed by 91 specimens of A. maslini, 48 of A. cozumela, 46 of A. rodecki, 62 of A. a. angusticeps, and 43 of A. d. deppii. Ellipses define 95% confidence boundaries for score distributions. (A) Principal component scores based on the model shown in Table 1. Percentages represent the proportion of meristic variation accounted for by principal components PC1 and PC2. (B) Plot of canonical variate scores based on the model shown in Table 1. Percentages represent the proportion of the discrimination accounted for by canonical variates CV1 and CV2.
Morphological meristic variation expressed by 96 specimens of A. maslini, 49 of A. cozumela, and 46 of A. rodecki. Ellipses define 95% confidence boundaries for score distributions. (A) Principal component scores based on the model shown in Table 1. Percentages represent the proportion of meristic variation accounted for by principal components PC1 and PC2. (B) Plot of canonical variate scores based on the model shown in Table 1. Percentages represent the proportion of the discrimination accounted for by canonical variates CV1 and CV2.
Chromosomes of three forms of Aspidoscelis: (A) (left of vertical line). The pair of Set I metacentric chromosomes of maternal A. a. angusticeps (UAZ 29433). (B) Karyotype of parthenogenetic A. maslini with 1 + 26 + 24, from Ramate, Guatemala (UAZ 27692); the Set I chromosome is clearly submetacentric and there are two more microchromosomes than expected from ancestral A. angusticeps (upper row) and A. deppii (lower row). (C) Karyotype of parthenogenetic A. cozumela with 0 + 28 + 21, from Isla Cozumel, México (UAZ 29315); the expected Set I chromosome is represented by two extra telocentric Set IIs and there is one less microchromosome than expected from ancestral A. angusticeps (upper row) and A. deppii (lower row); arrow indicates dot-like terminal satellite. Scale bar between B and C represents 10 microns.
Two alternative hypotheses for possible sequence of events in the evolution of karyotypic clones presently identified in the A. cozumela complex.
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