Parental investment in social voles varies and is relatively independent of litter size

In order to ascertain the typical pattern and amount of parental care in the social vole (Microtus socialis guentheri) as well as the individual investment of the female, male, or both parents simultaneously, we studied ten primiparous females and their mates. Results revealed that out of seven parental behaviors, only crouching was correlated with litter size, suggesting that parental care was relatively independent of litter size - that is, duration of time spent with the young, licking them, retrieving them to the nest, having them attached to the female's nipples, and searching for a nipple on the male were not correlated with litter size. Individual investment of caretakers also varied, with no typical proportion of shared nurturing by the female and male. Accordingly, overall parental investment varied greatly among different sets of parents without correlation to the relative contribution of the female, the male, or both. Finally, duration and frequency of most parental behaviors declined over the course of postnatal development. Altogether, these data suggest a surplus parental investment that was probably not required for survival of offspring but might have evolved either for other purposes such as the formation of social bonds or was selected for in captivity.