Effects of a pleistocene barrier on herpetofaunal distributions in southwestern North America




Rosenthal, Jonas

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Lake Cabeza de Vaca existed in the northern portion of the Chihuahuan Desert during the Pleistocene, possibly limiting taxon ranges and driving diversification of taxa by sundering once continuous populations occurring across this region. I reevaluate phylogenetic studies in light of evidence of Cabeza de Vaca and present molecular data that addresses the biological influence of the lake. Supplementing our reevaluations of previous studies, we identified taxa likely to show genetic differentiation consequent of the lake and tested them. Specimens from the colubrid snake Rhinocheilus lecontei and the phrynosomatid lizard taxa Phrynosoma cornutum and Urosaurus ornatus were collected, followed by DNA sequencing of a mitochondrial gene region that included Nicotinamide Adenine Dinucleotide subunit 4 (ND4), and the tRNAs Serine, Histidine, and Leucine. Phylogenetic analyses using maximum likelihood and Bayesian methods were used to construct evolutionary relationships between individuals of each taxo based on the obtained nucleotide sequences. In order to determine if correlations existed between sequence data variation and geography, haplotype networks were constructed and nested clade analysis was performed on P. cornutum using a combined data set that included other available sequence of the ND4 gene region. Deep molecular divergences were found within each taxon from specimens collected across the northern Chihuahuan Desert. Application of a molecular clock using three calibration rates suggests that the divergences predate the age of the lake. Orogeny of the southern extension of the Rocky Mountains in the Miocene and Pliocene likely produced the molecular signatures recovered in each taxon. These findings corroborate a more widely known hypothesis invoked to account for the split of the Sonoran and Chihuahuan Desert faunas.



Pliocene-Pleistocene boundary, organisms, reptiles, amphibians, Chihuahuan Desert


Rosenthal, J. (2005). Effects of a pleistocene barrier on herpetofaunal distributions in southwestern North America (Unpublished thesis). Texas State University-San Marcos, San Marcos, Texas.


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