Male-Related Pheromones and the Activation of Female Reproduction in the Prairie Vole (Microtus-Ochrogaster)
In virgin female Microtus ochrogaster, increases in uterine weight, indicative of reproductive activation, were observed as early as 20 days of age. Exposure to an unfamiliar adult male for a period of 1 h or less induced, within 48 h, increases in uterine weight lasting for at least 10 days. Applications of male urine induced increases in uterine weight equivalent to those observed in females exposed to additional visual, auditory, and olfactory stimuli from the male; urine from castrated males was less effective than urine from intact males. Direct physical contact with intact males or their urine was essential to reproductive activation, and visual or air-borne cues were not adequate. Sibling male-female pairs of this species do not ordinarily reproduce, probably due to the failure of the female to become reproductively active. Estrus and subsequent reproduction were induced, however, by applications of sibling male urine to the female’s upper lip, suggesting a behavioral barrier to reproduction among siblings.