Polymorphism at the avpr1a locus in male prairie voles correlated with genetic but not social monogamy in field populations.

Integrative studies of genetics, neurobiology and behaviour indicate that polymorphism in specific genes contributes to variation observed in some complex social behaviours. The neuropeptide arginine vasopressin plays an important role in the regulation of a variety of social behaviours, including social attachment of males to females, through its action on the vasopressin 1a receptor (V1aR). In socially monogamous prairie voles (Microtus ochrogaster), polymorphism in the length of microsatellite DNA within the regulatory region of the gene (avpr1a) encoding the V1aR predicts differences among males in neural expression of V1aRs and partner preference under laboratory conditions. However, understanding the extent to which V1aR mediates variation in prairie vole social and reproductive behaviour observed in nature requires investigating the consequences of avpr1a polymorphism and environmental influences under ecologically relevant conditions. We examined the relationship between avpr1a length polymorphism and monogamy among male prairie voles living in 0.1 ha enclosures during a time similar to their natural lifespan. We found no evidence that avpr1a genotype of males predicts variation in social monogamy measured in the field but some indices of social monogamy were affected by population density. Parentage data indicated that a male's avpr1a genotype significantly influenced the number of females with which he sired offspring and the total number of offspring sired. Total brain concentrations of V1aR mRNA were not associated with either male behaviour or avpr1a genotype. These data show that melding ecological field studies with neurogenetics can substantially augment our understanding of the effects of genes and environment on social behaviours.

Preference for own versus conspecific pups by inbred and outbred rats.

Communal care of young may occur when related females live in close proximity to each other. The degree of relatedness between females may affect discrimination of own from conspecific young. Retrieval tests were used to examine preference for own versus conspecific pups by inbred and outbred rats. Dams were given retrieval tests in a neutral arena every other day from day 1 through 10 postpartum. Outbred, but not inbred, dams showed a significant preference for their own pups. Outbred dams also retrieved pups more slowly than did inbred dams. Differences in the behavior of dams and/ or similarity of cues presented by pups may be responsible for the lack of preference for own pups shown by inbred dams. The results of this study suggest that indiscriminate care of young should occur when closely related females share a nest.

Age of pairing affects reproduction in prairie voles.

The effect of the age at pairing on reproduction of weanling prairie voles was studied. The proportion of pairs producing a litter within 60 days was influenced significantly by the age at pairing. More voles paired at 31 days of age produced litters than those paired at 21 days of age. Assuming a gestation interval of 21 days, the earliest mating occurred around 33 days of age in both groups. On average, successful matings did not occur until voles were housed together for 2 to 3 weeks. No other measured variables were affected by age of pairing.

Management, breeding, and reproductive performance of pine voles.

Pine voles (Microtus pinetorum) serve as an interesting rodent model for studies of fossorial adaptation and mammalian mating systems. They are unusual among rodents in displaying a cooperative system of breeding. Here we describe the management of a breeding colony of pine voles. This species is relatively easy to maintain in the laboratory, although care must be taken to provide sufficient water in their diet. Details of reproduction, as well as growth and development of the young, are included. Pine voles have a smaller litter size (2.3 +/- 0.9 pups at birth) than do other arvicoline rodents but are still prolific breeders, producing, on average, a litter per month for more than 12 months. These rodents are useful for comparison with other arvicoline rodents, as well as providing an opportunity to investigate the behavior, physiology, and reproduction of an easily managed cooperatively breeding mammal.

Mechanisms of reproductive suppression in female pine voles (Microtus pinetorum).

In co-operatively breeding birds and mammals, philopatric females are often reproductively suppressed. Many studies have focused on the functional significance of reproductive suppression, but further investigation of the mechanisms involved is required for a complete understanding of this process. This study investigated whether reproductive suppression in non-reproductive female pine voles (Microtus pinetorum) occurs as a result of lack of gamete maturation or lack of increase in LH. The behaviour of male pine voles was also examined to determine whether they show a preference for the mother versus her daughter, as lack of male stimulation may inhibit an increase of LH in daughter pine voles. Ovarian development and circulating LH concentrations were investigated in females housed with a prospective mate in the presence or absence of a parent. Maturation of gametes was not affected by the presence of a parent. In the presence of the mother, there was no increase in LH, as was observed in females housed with or exposed to a novel male. Males spent more time with mothers and possibly showed a preference for mating with the mother. These results are consistent with the contention that ovulation does not occur in female pine voles housed in the presence of their mother; however, it is not clear whether the lack of ovulation is caused by lack of stimulation from the male or suppression by the mother.

Chemical cues are necessary but insufficient for reproductive activation of female pine vole (Microtus pinetorum).

Among various arvicoline rodents, reproduction is influenced to varying degrees by social factors, including behavioral or chemical cues. Since previous research suggested that chemosignals from adult males reproductively activate female pine voles (Microtus pine-torum), we sought to determine specifically what types of stimuli promote the activation response. In these experiments, female were exposed to unfamiliar adult males, or to some combination of cues from males, or were housed alone. Using uterine mass as a measure of reproductive activation, we found that females were not activated by exposure either to male urine by itself or to male-soiled bedding by itself, but full contact with a male clearly resulted in heavier uteri. Females whose vomeronasal organs were surgically excised failed to undergo reproductive activation when housed with males. Finally, females allowed physical contact by being housed directly underneath males had heavier uteri than did females whose housing allowed contact only with the chemical cues from males. Among female arvicoline rodents, it appears that there exists a physiological continuum between absolute dependence on both contact and chemical cues from males vs. absolute independence for reproductive activation. The present results place female pine voles closer to the former extreme than to the latter.