Histocompatibility differences in wild mice; further evidence for the existence of deme structure in natural populations of the house mouse.

T has been knolwn to ecologists for some time that the commensal house mouse, I Mus muscuhs, has rather limited range of movement and that the mouse populations in different buildings are isolated from each other [see BLAIR (1953) for review]. It was also known that the different local groups differed in the frequencies of some genetically controlled traits (WEBER 1950; DEOL 1958; DUNN 1957). The subdivision of natural mouse populations into more or less isolated groups was furthermore required on some theoretical grounds. Most of the natural populations of this species are polymorphic for alleles at the T-t (Brachyury) locus (DUNN 1957). Calculations of the expected t-allele frequencies based on random mating and infinite population size led to a sharp discrepancy with frequencies actually observed (BRUCK 1957; DUNN and LEVENE 1961). To bring the expected and observed frequencies into agreement it must be assumed that the geographical population of the house mouse consists of small endogamous breeding units, or demes (LEWONTIN and DUNN 1960). On the basis of their cage population studies, REIMER and PETRAS (1967) postulated that a deme consists of a dominant male, several females, and several subordinate males. Empirical evidence for the existence of demes in the natural population was provided by studies of t alleles (ANDERSON 1964), protein variants (PETRAS 1967), and H-2 polymorphism (KLEIN 1970). In this paper we present additional evidence from a study of histocompatibility differences in wild mice. It was calculated that two different inbred strains of laboratory mice differed in at least 15 (BARNES and KROHN 1957) to 29 (BAILEY and MOBRAATEN 1969) histocompatibility ( H ) loci. All these loci can be studied simultaneously by tissue transplantation. In the present study skin grafting was used for comparison between mice of the same and geographically distant localities and for the calculation of the number of histocompatibility loci showing effective segregation in the wild population.