Ovaries of meadow voles, Microtus pennsylvanicus, after copulation with a series of males.

Abstract

Female meadow voles, Microtus pennsylvanicus, were paired with a series of four males. Each male, except the first, interrupted the pregnancy caused by the preceding male and initiated a further ovulation and pregnancy. These events were reflected in vaginal-smear patterns. The ovaries of these voles were compared with those obtained from primiparous and multiparous females killed after copulation. No significant differences in ovarian weight were observed among the three groups. The number of corpora lutea per vole varied from 20.0 ± 1.3, in the repeatedly mated group, to 5.6 ± 0.4 and 5.9 ± 0.5, respectively, in the primiparous and multiparous groups. The data are compared with published information on ovaries of wild microtines. High numbers of corpora lutea in the ovaries of wild microtines, such as Microtus spp. and Clethrionomys glareolus. which nave been shown to be induced ovulators, may be taken as suggestive evidence of pregnancy failure in nature.