Date of Award

Fall 12-1-1981

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Life Sciences

First Advisor

John O. Whitaker Jr.

Second Advisor

William J. Brett

Third Advisor

Joseph F. Albright

Abstract

This study was undertaken to determine specific and intraspecific relationships within the genus Zapus (Mammalia, Rodentia, Zapodidae). Subspecies are based on the biological subspecies concept where the subspecies is an evolutionary step between a population and species. Approximately 20,000 Recent specimens and representatives of fossil taxa were examined. Cranial and postcranial characteristics, colors, and when available bacula, sperms and karyotypes were incorporated into the morphological analyses. In addition, published biological data were summarized and analyzed for evidence of primary and secondary isolating mechanisms. Supplemental data were acquired during collection of 450 specimens in midwestern and western United States, western Canada, and Alaska. The ancestor of living Zapus was Zapus rinkeri-like. A population of this progenitor was apparently isolated by the glacier and meltwater Mississippi River in what is now southeastern United States; there it speciated into Zapus hudsonius. Other populations were isolated in the southwestern United States, the Sierra Nevada Mountains, and along the west coast from San Francisco to southwestern British Columbia. These peripheral populations, including Zapus hudsonius, closely resemble each other. As a result of environmental drying, perhaps during the Xerothermic Period (4000-6000 years B. P.), the western and southwestern peripheral populations were isolated. Coincidentally, an interior population speciated, apparently in the central Rocky Mountains; the resulting derived phenotype is that of Zapus princeps in the central portion of its range. Zapus hudsonius and z. princeps are sympatric in North Dakota and Minnesota, Colorado, and British Columbia. The two species can be discriminated by the nature of the paracone of the Ml and M2. In 1· hudsonius, it is not connected to the rest of the occlusal pattern; the first primary and first secondary folds are continuous medially. The paracone of ~- princeps, however, is broadly connected; the first primary and first secondary folds do not converge. The two species maintain their integrity in these areas. However, when the derived form (i.e., 1· £· orinceps) contacts the southwestern and Pacific coast populations there is extensive intergradation. The populations in northern New Mexico are a blend of the primitive (i.e., peripheral) and derived forms. However, the populations in southern New Mexico and eastern Arizona remain isolated, retaining the primitive phenotype, as did a population in Edwards County, Texas, known only from fossils. The subspecies 1· £· luteus is retained for these isolated southwestern populations. In the Northwest, extensive intergradation occurs from southern Idaho westward to coastal Oregon and south into California. The population in Marin County, California is isolated by the Sonoma-Marin Gap and Sacramento Valley and has retained its integrity; this is~-£· orarius. The populations in the Sierra Nevada Mountains are also distinct and apparently isolated; they are grouped under f. princeps pacificus. The derived form of Zapus princeps invaded Washington via the Cascade Mountains. Intergradation occurs from the area of Mt. Rainier southwest, west, and north along the coast. A second route to this coastal region occurs in the area of Manning Provincial Park, British Columbia. Although there is evidence of intergradation, the populations of Zapus princeps isolated in the Raft River Mountains, Utah and Idaho comprise the only interior population which retains the primitive phenotype. This is z. £· cinereus. There are two dental phenotypes off. hudsonius, one in northwestern (e.g., Alaska, British Columbia) and the other in eastern North America. This suggests an isolated population in the unglaciated portion of Alaska, in a manner similar to that theorized in the Southeast. The two forms intergrade in Ontario. There is no evidence of any population of Zapus hudsonius being sufficiently isolated or distinct to warrant subspecific status.

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