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Abstract:
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Pocket gophers are known for their fossorial lifestyle, small isolated populations, and low fecundity. These characteristics make pocket gophers an ideal group for examining rate heterogeneity and sequence divergence in light of recent hypotheses concerning metabolic-rate and body size. To test these hypotheses, the mitochondrial 12S ribosomal (rRNA) gene was sequenced from individuals representing 10 species of the genus Geomys. In addition, specimens of Cratogeomys castanops. Thomomvs bottae. T^ umbrinus. Dipodomvs philHpsii. and Pedetes capensis were examined as outgroups. Specifically, the goals of this study were to: (1) determine if heterogeneity existed in rates of sequence divergence between fossorial and nonfossorial rodents, (2) determine intrageneric nucleotide sequence variation at the 12S rRNA gene, and (3) determine if the 12S rRNA gene contains phylogenetic signal to resolve the phylogenetic relationships within Geomys. The overall levels of 12S rRNA sequence divergence observed (average 3.5, range 0.6-7.5) support a low level of divergence within Geomvs. with the overall transition/transversion ratio lower than that observed in other mammalian groups. Relative rate tests did not detect significant overall levels of rate heterogeneity within and among Geomvs and outgroup taxa, nontheless certain taxa did show rate heterogeneity when compared to other members within group. The resultant 12S rRNA gene phylogenies provided strong phylogenetic signal and consistently supported several relationships within species and subspecies of Geomvs. |