Female prairie voles (Microtus ochrogaster) fail to form a new pair after loss of mate.

We tested experimentally the hypothesis that failure to acquire a new mate by monogamously paired female Microtus ochrogaster that lose their mate represents pair-bonding behavior, not a lack of available males. Males were removed from reproductive male-female pairs and the females provided an opportunity to pair with unfamiliar sexually inexperienced or experienced males in a semi-natural arena. Only three of 22 (13.6%) females formed a new pair, two with inexperienced males and one with an experienced male. Three other females spent more time with an experienced male than with the inexperienced male, but did not form a pair or co-nest with that male. The results confirm field observations that availability of males is not a factor in the failure of female prairie voles to form a new pair following loss of their mate. This study concludes failure to form a new pair is associated with pair-bonding behavior.

Physiological substrates of mammalian monogamy: the prairie vole model.

Prairie voles (Microtus ochrogaster) are described here as a model system in which it is possible to examine, within the context of natural history, the proximate processes regulating the social and reproductive behaviors that characterize a monogamous social system. Neuropeptides, including oxytocin and vasopressin, and the adrenal glucocorticoid, corticosterone, have been implicated in the neural regulation of partner preferences, and in the male, vasopressin has been implicated in the induction of selective aggression toward strangers. We hypothesize here that interactions among oxytocin, vasopressin and glucocorticoids could provide substrates for dynamic changes in social and agonistic behaviors, including those required in the development and expression of monogamy. Results from research with voles suggest that the behaviors characteristics of monogamy, including social attachments and biparental care, may be modified by hormones during development and may be regulated by different mechanisms in males and females.

Reproductive activation of virgin female prairie voles (Microtus ochrogaster) by paired and unpaired males.

Virgin female Microtus ochrogaster were exposed to paired and unpaired unfamiliar adult males in semi-natural arenas. Although females were reproductively activated by both types of males, more than twice as many were activated by unpaired (51.6%) as by paired (18.2%) males. Our results suggest that, in natural populations of prairie voles, the proportion of philopatric females becoming reproductive is related to the abundance of unpaired males within the population.

Multiple exposures to adult males and reproductive activation of virgin female Microtus Ochrogaster.

Virgin female Microtus ochrogaster living in family groups were reproductively activated by twelve 1-hr exposures over a 3-day period to unrelated sexually experienced males. Reproductive activation among virgin females receiving six or eight exposures over a 2- or 3-day period did not differ significantly from that of unexposed control females. Thus, frequent multiple exposures to unfamiliar males (and repeated stimulation by a male urinary chemosignal) can override the reproductive suppression typically experienced by virgin females remaining in family groups.

Suppression of reproductive maturation in male-stimulated virgin female microtus by a female urinary chemosignal.

Urine from female Microtus ochrogaster possesses a chemosignal that suppresses reproductive maturation in other females. Uterine enlargement in virgin females stimulated by a male was suppressed by subsequent association with another female or by application of female urine on the nose. Females so suppressed are not able to achieve estrus. Urine from virgin sibling and non-sibling females and from pregnant females possesses the suppressing effect.

Male vole urine changes luteinizing hormone-releasing hormone and norepinephrine in female olfactory bulb.

Female prairie voles (Microtus ochrogaster) exposed to a single drop of male urine on the upper lip showed changes in concentrations of luteinizing hormone-releasing hormone (LHRH) and norepinephrine in olfactory bulb tissue; no such changes occurred in dopamine concentration. The changes were measured in the posterior but not the anterior olfactory bulb tissue of females within 1 hour after they were exposed to urine. These females also showed rapid increases in serum concentrations of luteinizing hormone. Females exposed to water on the upper lip showed none of these changes. These results suggest that in this species LHRH and norepinephrine in the olfactory bulb may mediate luteinizing hormone release in response to external (pheromonal) chemical cues.