Genetics of hybridization between the pocket gophers Thomomys bottae and Thomomys townsendii in northeastern California

Hybridization between the pocket gophers Thomomys bottae and T. townsendii at Cold Run Creek in Honey Lake Valley, Lassen County, California, is examined by electromorphic and morphologic characters and by the distribution of ectoparasitic mallophagan lice. Hybrid formation is minimal (about 12% of the total sample of 104 individuals examined), but both F1 hybrids and a few presumptive backcross individuals are apparent. Nevertheless, no evidence of genic introgression based on five diagnostic allozyme loci is present in parental populations of either taxon within a mile of the hybrid zone. Similarly, louse species unique to each parental gopher host do not penetrate beyond the geographic limits of the genetic hybrid zone into the range of the opposite gopher species. A narrow zone of hvbridization is thus concordantly defined by genetic, morphologic, and ectoparasitic parameters. These two gopher taxa are thus genetically if not reproductively isolated and should be considered separate biological species.