Young, sexually naive prairie voles (Microtus ochrogaster), 21-60 days of age, of both sexes readily exhibit alloparental behavior toward pups without apparent hormonal or experiential priming. The goal of the present study was to quantify the incidence of spontaneously evoked alloparental behavior in young prairie voles and determine prior pup experience (i), gender-related (ii) and age-related (iii) characteristics, and hormonal (iv) and housing (v) conditions associated with alloparental behavior. Overall, 70% of all prairie voles between 21 and 60 days of age exhibited alloparental behavior regardless of hormonal condition or postweaning housing condition (single versus sib-group housing). Experience with pups prior to weaning was associated with a greater percentage of prairie voles exhibiting alloparental responding in comparison with prairie voles that had never been exposed to pups. Male prairie voles were more likely to be alloparental than were females, although most females (64%) exhibited alloparental behavior. Differences in qualitative variables associated with alloparental responsiveness were present between prairie voles <40 days of age and those >=40 days of age, although both age groups responded parentally in equal numbers. This study suggests that although a short period of prior experience may promote the expression of alloparental behavior in young prairie voles, alloparental behavior occurs in most animals in all groups examined. Hormonal, sex-related or age-related changes that might be associated with development, reproductive suppression, or social stress are not related to the differential expression of alloparental behavior.
