PROTEIN POLYMORPHISM AND GENIC HETEROZYGOSITY IN TWO EUROPEAN SUBSPECIES OF THE HOUSE MOUSE.

Abstract

A recent survey (Selander and Yang, 1969) of electrophoretically demonstrable genetic variation in proteins in a population of wild house mice (Mus musculus) from Hallowell Farm, Ramona, California, provided a basis for estimating the proportion of polymorphic loci in the total genome. Of 40 loci controlling the 35 enzymes and non-enzymatic proteins studied, 30% were polymorphic, a proportion closely similar to those available for Drosophila pseudoobscura (Lewontin and Hubby, 1966) and for man (Harris et al., 1968; Lewontin, 1967). Because this estimate was based on an analysis of a single population assigned taxonomically to one subspecies (M. m. brevirostris) and derived from ancestral stocks introduced from Europe to North America within historical times (Schwarz and Schwarz, 1943), it seemed desirable to extend the investigation to additional populations and subspecies. In the present paper, we have surveyed electrophoretic protein variation in six samples representing two subspecies of the house mouse, M. m. musculus and M. m. domesticus, occurring in Denmark. Our objectives are to obtain estimates of total genic heterozygosity for comparison with that available for the California population, and to assess the overall degree of genetic difference between the two subspecies, utilizing the loci investigated as a representative sample of the total genome. A genetic comparison of the Danish populations should be of special interest to students of speciation, since M. m. musculus and M. m. domesticus are, in fact, evolutionary semispecies, having acquired many of the attributes of species rank (Mayr, 1963), including conspicuous morphological and behavioral differences. Despite the existence of a zone of allopatric hybridization between the two forms in central Jutland, there appears to be little gene flow between them (Ursin, 1952; and an investigation of protein variation in progress by Hunt). With the Danish material, we have the opportunity to estimate the degree of genetic difference attained by allopatric populations at the critical stage of speciation where coadapted genetic systems are closing and species are forming.