Postimplantation pregnancy disruption in Microtus ochrogaster, M. pennsylvanicus and Peromyscus maniculatus

The Bruce effect, the inhibition of pregnancy by a 'strange' male before implantation (Bruce, 1959), has been demonstrated in house mice, Mus musculus (Bruce, 1959; Chipman & Fox, 1966), prairie deermice, Peromyscus maniculatus bairdii (Eleftheriou, Bronson & Zarrow, 1962), field voles, Microtus agrestis (Clulow & Clarke, 1968), prairie voles, M. ochrogaster (Stehn & Richmond, 1975), and meadow voles, M. pennsylvanicus (Clulow & Langford, 1971). In their study of prairie voles, Stehn & Richmond (1975) described a postimplantation disruption of pregnancy by a non-stud male as late as Day 17 of the 21–23-day pregnancy, and they ascribed this prolonged susceptibility to factors associated with the occurrence of reflex ovulation in these voles. We therefore examined the effect of a 'strange' male on pregnancy in prairie and meadow voles, species in which ovulation is induced by copulation, and in prairie deermice which are spontaneous ovulators.