Control of ovulation, vaginal estrus, and behavioral receptivity in voles (Microtus).

Rodents of the genus Microtus provide an excellent focus for the study of the effects of environmental and behavioral influences on reproductive physiology. Despite some early reports, there is little definitive evidence of truly spontaneous ovulation in Microtus. Stimuli from copulation with males appear capable of triggering ovulation in all species: the requisite amount of stimulation for ovulation and a functional luteal phase varies with the species. In addition, however, a certain percentage of the females of some, but not all, species ovulate when placed in proximity to males when copulation is presented. There are few reports of regular cycles of cell types in the vaginal smears of Microtus females; the relative preponderance of cornified, nucleated, and leukocytic cells varies with species and conditions. Behavioral receptivity is not invariably correlated with smear type. The complexity of environment-behavior relationships in different species suggests the need for a more comprehensive classification schema for systems of female reproductive physiology and a study of their adaptive significance.