Effect of vomeronasal organ removal on behavioral estrus and mating latency in female meadow voles (Microtus pennsylvanicus).

The vomeronasal organ (VNO) mediates the induction of behavioral estrus in prairie voles by male chemosignals; however, the importance of this system for the initiation of estrus in meadow voles, a species in which spontaneous estrus has been postulated, is unknown. This experiment was designed to investigate the influence of VNO-mediated chemosensory information on behavioral estrus in meadow voles housed in photoperiods simulating summer (long photoperiods; 14L:10D) and winter (short photoperiods; 10L:14D). The VNO was removed from nulliparous female meadow voles, and the percentage of animals mating after removal and the timing of mating onset were assessed. Removal of the organ did not suppress mating or change the timing of mating onset in females housed in short photoperiods. In animals housed in long photoperiods, in contrast, removal of the organ significantly increased the percentage of females mating and the percentage of females mating rapidly after pairing. The results indicate that chemosensory information mediated via the VNO is not necessary for the induction of behavioral estrus in meadow voles and lends support to the hypothesis that meadow voles have a spontaneous estrus. We postulate that polygynous, solitary meadow voles reproduce more effectively with spontaneous estrus than with the induced estrus described for monogamous, group-living prairie voles.