Browsing by Subject "Rodents -- Evolution"
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Item Molecular systematics of the genus Sigmodon(Texas Tech University, 1998-12) Peppers, Lottie LThe genus Sigmodon is comprised of six North American (S. alleni, S. arizonae, S.fidviventer, S. leucotis, S. mascotensis, and S. ochrognathus), three South American (5. alstoniy S. inopinatus^ and S. peruanus), and one widespread species {S. hispidus) found in both North and South America. Phylogenetic relationships among cotton rats are poorly understood due to a lack of morphological differentiation among taxa and the absence of comprehensive studies involving both North and South American forms. This study addressed phylogenetic relationships among members of the hispidus ondfulviventer groups, monophyly of South American taxa, and genetic differentiation within 5. Hispidus by assessing nucleotide sequence variation in the mitochondrial cytochrome b gene. Results of phylogenetic analyses do not support the conventional hispidus and fulviventer groups. South American taxa do not form a monophyletic unit, and 5. hispidus appears to contain several cryptic species. Percent sequence divergence values between currently recognized species ranged from 8.2 to 21.8 percent, and indicate either an earlier date of diversification than traditionally accepted, or an accelerated rate of molecular evolution.