Biochemical Polymorphism and Systematics in the Genus Peromyscus. III. Variation in the Florida Deer Mouse (Peromyscus floridanus), a Pleistocene Relict

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. The large and successful rodent genus Peromyscus includes about 60 named species, variously assigned to five to seven subgenera (Osgood, 1909; Hall and Kelson, 1959; Hooper and Musser, 1964; Hooper, 1968). The diversity in size of geographic range and in pattern of recognized geographic variation in morphology among nominal Peromyscus species is striking. Roughly one-half of the species are monotypic, exhibiting no definable geographic variation in morphology (Baker, 1968). Most monotypic species, such as P. stephani and P. dickeyi, are insular endemics, but a few others such as P. melanotis are continental and occupy larger ranges. Similarly, polytypic species consisting of more than one named subspecies may have narrow (P. sitkensis) or wide (P. maniculatus) geographic ranges. In this study, we continue our biochemical survey of the genus Peromyscus by examining geographic variation in electromorphic content of species belonging to the truei and maniculatus species groups of the subgenus Peromyscus. We are particularly interested in the systematic and evolutionary ramifications of contrasting patterns of geographic genetic differentiation. Peromyscus maniculatus is probably the most widespread and abundant small mammal on the North American continent. Populations referable to some 65 named subspecies are distributed from southern Mexico to the Northwest Territories of Canada, and from the Pacific to North Atlantic seaboards. The diversity of occupied habitats ranges from arid grasslands and brushy slopes to humid coniferous and deciduous forests. We have examined allozymic variation in proteins encoded by 21 genetic loci in a total of 716 P. maniculatus collected throughout most of its range. We have also examined several populations of a more narrowly distributed sibling...

Isoenzyme variation in the common shrew (Sorex araneus) in Britain, in relation to karyotype

“…Therefore it is considered more likely to have come about by genetic drift permitted by at least a temporary reduction of gene flow between close sites than the result of local selection pressures. Similar heterogeneity in allele frequencies has been demonstrated in other small mammals, e.g., house mouse (Selander, 1970), Florida deer mouse (Smith et a!., 1973). It is perhaps surprising that there should be such genetic subdivision in the common shrew, as this species is catholic in its habitat requirements (Corbet, 1966) and it is wellknown from ecological studies that adult male common shrews roam widely during the breeding season in search of mates (Shillito, 1963;Buckner, 1969), a factor which should greatly promote gene flow.…”

Electrophoretic Comparisons between Allopatric Populations of Five Australian Pseudomyine Rodents (Muridae)

“…If the same situation applies to rodents, then electrophoresis becomes a powerful tool for determining the specific status of allopatric populations. Selander et al (1971), Smith et al (1973) In order to test this possibility, we have compared the levels of taxonomic differentiation, in terms of 'apparently fixed' differences, between taxonomic levels of various rodent groups from data available in the literature. An 'apparently fixed' difference was defined for the purposes of this analysis as one in which one allele at a locus occurred at a frequency of greater than 90 % in one taxon and less than 10% in the other taxon (corresponding to a genetic similarity of less than 0,2).…”

THE GENETICS OF SPECIATION IN THE RODENT GENUSPEROMYSCUS

“…Whereas studies by several investigators (Avise et al, 1974a,b;Bowers et al, 1973;Garten, 1976;Jensen, 1970;Jensen and Rasmussen, 1971;Johnson and Packard, 1974;Selander et al, 1971;Smith et al, 1973) have increased our understanding of the genetics of various other species of Peromyscus, quantification of the amount of genomic modification accompanying speciation has not been thoroughly examined. Data now available from our studies permit us to assess the genetics of speciation at five levels of differentiation among six of the seven species groups of the subgenus Peromyscus.…”