Biosystematics of the genus Reithrodontomys on the Southern High Plains

Determining and understanding evolutionary relationships of organisms is a goal in systematics. Initial studies of the genus Reithrodontomys addressed the subspecific affinities of species within the genus in portions of their ranges (Hooper 1952; Jones and Mursaloglu 1961). The focus of subsequent investigations has evolved beyond the taxonomic level of the subspecies, and has paralleled the development of new genetic and molecular techniques, such as standard karyotype analysis (Shellhammer 1967; Carleton and Myers 1979; Engstrom et al. 1981), G- and C- banding of chromosomes (Robbins and Baker 1980), starch-gel electrophoresis of allozymes (Arnold et al. 1983), and most recently, in situ hybridization of satellite DNA (Hamilton et al. 1990). Thus, many of the questions regarding Reithrodontomys pertain to phylogenetic relationships. Despite the many studies of Reithrodontomys, important questions relative to variation among populations of species within the genus remain unanswered.

Reithrodontomys megatotis, from the Southern High Plains in West Texas, represents a taxon in which variation within and among populations is not well understood. This species Is a relatively rare or elusive inhabitant of the area, and to date, these characteristics have prevented a thorough study of populational differences in this geographical region. Currently, two subspecies (R m. aztecus, R. m. megatotis), are recognized rom this expanse in West Texas. The purpose of this study is to examine specimens from this region, and through the use of phenetic techniques and statistical analyses, elucidate the extent of nongeographic and geographic variation in R. megatotis, and assess the subspecific status of R. megatotis on the Southern High Plains.