Further observations on the influence of the social environment on ovulation in the vole, Microtus agrestis.

Although members of the species Microtus agrestis are induced ovulators (Austin, 1957; Breed, 1967), ovulation may be induced by stimuli other than those associated with mating, e.g. when females are separated from adult males by wire mesh (Milligan, 1974). Tactile contact between the sexes is not necessary for this ovulatory response as ovulation still occurred when two barriers of mesh, 2\m=.\5cm apart, separated the male and female (Milligan, 1974). The present experiments continued the investigation of the nature of the effective stimuli for ovulation which are provided by non-coital contact with a male. Laboratory bred voles from the `mixed-type' colony described by Milligan (1974) were used. Males were fertile adults from the breeding colony; all females had shown cornified vaginal smears on 3 consecutive days before the experiments. In Exp. 1, virgin females were treated as shown in Table 1. The females were housed individually on a wire-mesh floor supported 5 cm above the normal solid floor of a wire-topped plastic cage (29\m=x\19\m=x\10 cm). A plastic box (17\m=.\5\m=x\11\m=.\5\m=x\6\m=.\0 cm), open at the bottom, was placed on the wire floor; this box contained a male in Exps 1B and 1C. Faeces and urine from males and females passed through the mesh of the floor and thus the females in Exps 1B and 1C were exposed to male odours. The sides of the box used in Exp. 1C