6-Methoxy-2-benzoxazolinone and photoperiod: prenatal and postnatal influences on reproductive development in prairie voles (Microtus ochrogaster ochrogaster)

Abstract

The effects of photoperiod and 6-methoxy-2-benzoxazolinone (6-MBOA) on the gonadal development of prairie voles was studied when this plant compound was available to pups in utero, during nursing, or postweaning. In part 1, pregnant voles exposed to long or short day lengths were fed food in which 6-MBOA was present (50 μg of 6-MBOA/g food) or absent prior to the birth of their young; all of these dams received a diet that lacked 6-MBOA after the pups were born. Other females were fed food without 6-MBOA throughout pregnancy, but received one of the diets during lactation. Short days inhibited reproductive development in male offspring, affected pup survival, and enhanced pelage development. Postnatal exposure to 6-MBOA did not affect the reproductive function of males. In contrast, prenatal exposure to 6-MBOA accelerated reproductive development among short-day males. Prenatal exposure to 6-MBOA did not affect survival of short-day males, but reduced survival of long-day pups. Prenatal 6-MBOA treatment affected the sex ratio of pups that survived until weaning (13:21; male:female) and of pups that died prior to weaning (26:5). In contrast, photoperiod did not affect reproductive function in female voles. Although reproductive function appears to be uncoupled from photoperiodic regulation, female prairie voles processed photoperiodic information; pelage development was enhanced among short-day females. In part II, breeding pairs were exposed to long or short days and fed food devoid of 6-MBOA prior to the birth of the young. On the day of birth, and for the following 3 weeks, either 6-MBOA-free or 6-MBOA-enriehed food was provided. After weaning, pups received their parents type of food until autopsy 3 or 7 weeks later. Again, photoperiod affected male, but not female, reproductive function. No consistent pattern of results from postnatal exposure to 6-MBOA was discerned for either males or females. Acceleration of reproductive function among short-day males because of prenatal influences may, be involved in the rapid rate of sexual maturation observed prior to peak population densities of microtine rodents. Because males of this species induce females into estrus, male prairie voles may depend on environmental cues to regulate reproductive function, while females may respond only to males. The physiological and ecological implications of these data are discussed.