Geographic variation, species recognition, and molecular evolution of cytochrome oxidase I in the Tropidurus spinulosus complex (Iguania : Tropiduridae)
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Geographic variation and molecular evolution in mitochondrial cytochrome oxidase I were examined among 28 individuals representing 11 populations of the Tropidurus spinulosus complex in Paraguay and Brazil. Thirteen haplotypes were discovered with variation at 43 of 405 nucleotide positions. Polymorphisms were present in three geographic locations. All nucleotide substitutions were synonymous and predominantly C-T transitions at third codon positions. The minimum number of migration events required by most parsimonious mtDNA trees composed of all individual sequences was 11, decidedly fewer than predicted if haplotypes were distributed randomly. Phylogenetic analysis of 13 haplotypes revealed a tree with a basal dichotomy geographically consistent with separation of populations on either side of the Rio Paraguay. These transriver populations exhibited 5.0-7.5% sequence divergence between pairwise comparisons. The geographical barrier also was concordant with some geographic trends of squamation and adult coloration, Discordance of a few morphological characters with the molecular phylogenetic evidence may suggest that previcariance geographic variation in these features has persisted in the divergent lineages. Alternatively, convergence must be invoked to explain coherent geographic variation in morphological characters across well-supported molecular boundaries. Combining morphological characters with the mtDNA characters does not change topology of trees based on mtDNA characters alone. Populations east and west of the Rio Paraguay represent at least two distinct evolutionary lineages. Tropidurus guarani occurs on the eastern side of the Rio Paraguay, extending east and northeast into Mato Grosso do Sul and Goias, Brazil. We predict that additional data will reveal that T. guarani is composed of two lineages, and denote these species candidates as T. guarani 'Paraguari' and T. guarani 'Mato Grosso do Sul.' Tropidurus spinulosus occurs on the western side of the Rio Paraguay in the Argentinian, Paraguayan, and Bolivian Chaco.
