Systematic Relationships and Historical Zoogeography of the Desert Pocket Gopher, Geomys arenarius

Abstract

Evolutionary relationships of peripheral populations of pocket gophers of the genus Geomys in New Mexico were investigated using karyotypic and allozymic data. Analysis of previously undescribed karyotypes from populations geographically intermediate between G. bursarius knoxjonesi (2N = 70, FN = 70) and G. arenarius arenarius (2N = 70, FN ≈ 102) revealed an intermediate chromosomal complement (2N = 70, FN ≈ 88). Allozymic variation among populations of the two nominal species was generally of a smooth clinal nature, and no fixed allelic differences were detected, indicating the existence of gene flow between the two taxa. Based on these data, coupled with consideration of previous morphometric and ectoparasitic studies, G. arenarius is synonymized under G. bursarius. Geomys from the Rio Grande Valley in southern New Mexico and adjacent Texas and Chihuahua are herein referred to G. b. arenarius; populations from the Tularosa Basin and adjacent Jornada del Muerto in New Mexico are collectively referred to G. b. brevirostris. These peripheral populations apparently represent relicts of an expansion of G. bursarius into the area during more mesic Wisconsinan times.