Relationships of pocket gophers of the genus Geomys from the Central and Northern Great Plains

Abstract

Three species of pocket gophers of the genus Geomys exist in the Great Plains north of Texas. The northernmost of these, G. bursarius, consists of the widespread, variable nominate subspecies and two more restricted, less variable subspecies (G. b. illinoensis and G. b. wisconsinensis). The second species, from the central plains, G. lutescens, has two subspecies within the study area (G. l. lutescens and G. l. major), and one or more extralimital subspecies. The third species, G. breviceps, is represented in the southern plains (in Oklahoma) by G. b. sagittalis, and by several subspecies outside of our study area. All species are distinguishable on the basis of cranial morphology, karyology, and ectoparasite fauna, and show minor differences in bacula. All specimens previously thought to be intergrades between the three species were reexamined and found to be clearly assignable to one species or the other, with no evidence of intergradation. Hybridization between G. bursarius and G. lutescens occurs only at a single locality in Nebraska, and introgression there is inconsequential. Hybridization between G. lutescens and G. breviceps probably occurs in several places in east-central Oklahoma, but the hybrid zones are narrow, and gene flow appears to be restricted. Variation within all species is mostly clinal; non-clinal variation is thought to be due to the late-Pleistocene history of the gophers. Analysis of cranial and other characters indicates that G. bursarius and G. lutescens are recently derived from a stock similar to G. breviceps and G. personatus. Geomys pinctis had the most primitive features of the species considered, and was probably separated from the others at an early date.