Biochemical Polymorphism and Systematics in the Genus Peromyscus VII. Geographic Differentiation in Members of the Truei and Maniculatus Species Groups

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Abstract
Allozymic variation at 22 gene loci in populations of Peromyscus truei, P. difficilis, P. melanotis, and P. maniculatus is used to examine patterns of geographic differentiation. Samples of P. maniculatus collected throughout most of its immense range, from southern Mexico to northern Canada and from the Pacific to Atlantic coasts, are very similar in genic composition. Evidence from morphology, chromosomal configurations, ecology, and patterns of reproductive isolation argue that contemporary gene flow among P. maniculatus populations is not sufficient to account for the similarity in their allelic configurations. The macrogeographic conservatism in level of genic divergence conceivably results from relatively recent separation of populations, coupled with a genetic inertia resulting from a selected cohesion of the genome. Nonetheless, significant intersample heterogeneity of allele frequencies at polymorphic loci may certainly result from stochastic effects. The relative geographic uniformity in P. maniculatus contrasts somewhat with the geographic differences observed in P. truei and in P. difficilis. Members of the truei and maniculatus species groups are added to a biochemical dendrogram, which now includes 20 named species of Peromyscus.