Allozymic Variation and Systematics of Plains Pocket Gophers (Geomys) of South-Central Texas

Allozymic variation was analyzed for populations of seven taxa comprising five cytotypes of the Geomys chromosome complex in Texas. The genetic relationships of taxa from the central Texas Edwards Plateau, Geomys bursarius llanensis and G. b. texensis, were compared to G. b. major, Geomys knoxjonesi, Geomys attwateri, Geomys personatus, and Geomys breviceps. Geomys from the Edwards Plateau had from two to six fixed allelic differences with the other taxa. Isolation of the Edwards Plateau taxa precludes contact-zone analysis. Nevertheless, genetic differentiation is typical of that between other species of Geomys, and the Edwards Plateau taxa should be recognized as Geomys texensis. Phenetic analysis of genetic similarity among the six taxa indicated that G. texensis is most similar to G. knoxjonesi. Cladistic analyses indicated G. texensis is a sister taxon to G. bursarius. A vicariance model of speciation of G. texensis is supported by paleoecological data.