OCCURRENCE OF SUCCESSFUL MULTIPLE INSEMINATION OF FEMALES IN NATURAL POPULATIONS OF DEER MICE (PEROMYSCUS MANICULATUS)

The possibility that populations of' small mammals are subdivided into highly isolated demes of small size has been a point of contention in the literature. Much of the evidence supporting this demic structure concept has been accumulated by studies on house mice (Mus musculus) (e.g., Selander, 1970; Anderson, 1964, 1965). Anderson (1970) has used this evidence as support for a model of local population subdivision involving highly complex spatial and temporal structuring, which he suggests is likely to be characteristic of rodent populations in general. This paper is a report of direct evidence of frequent multiple male parentage within single litters in natural populations of deer mice (Peromyscus maniculatus). Thus in these populations the social units (if, in fact, they exist) must be large enough to include two, or probably more, breeding males. This is quite unlike the social structure described by Brown (1969) in Apodernus populations and Selander (1970) in Mus populations, in which one dominant male is thought to do most, if not all, of the breeding.