Biochemical Polymorphism and Systematics in the Genus Peromyscus. V. Insular and Mainland Species of the Subgenus Haplomylomys

Abstract

Biochemical polymorphism and systematics in the genus Peromyscus. V. Insular and mainland species of the subgenus Haplomylomys. Syst. Zool. 23:226–238.—We have examined allozymic variation at 25 loci in nine species of Peromyscus inhabiting the southwestern United States, Sonora, Baja California, and islands in the Gulf of California. Four previously studied species of Peromyscus are also included in a dendrogram formed by cluster analysis of genie similarity coefficients. Mainland populations currently assigned to P. eremicus represent two distinctive genetic types, an eastern form in Nevada, New Mexico, Arizona, Texas, and Sonora, and a western form in southern California and Baja that may have been separated originally by the Gulf of California embayment in the Pleistocene. Peromyscus merriami is genically distinct from sympatric P. eremicus populations of the eastern type, although it falls within the range of genetic variation found between eastern and western P. eremicus forms. The insular endemics P. guardia, P. interparietalis, and P. dickeyi, and two insular subspecies of P. eremicus, are similar to the western P. eremicus type on Baja and probably share a recent common ancestor. Populations on shallow-water islands near Baja are more similar to mainland populations than are those on deep-water islands. Other insular species, P. caniceps and P. stephani, are genetically more distinct from P. eremicus and may have closer relationships with other mainland species. P. sejugis is closely related to P. polionotus (maniculatus species group) and probably evolved from maniculatus. There is considerable variation in level of genie heterozygosity among mainland populations, although the mean of six percent is consistent with “normal” heterozygosity estimates for other vertebrates. All insular populations have low variability, averaging less than one percent of loci in heterozygous state, presumably as a consequence of random drift in small populations.