Seasonal plasticity of maternal behaviour in Peromyscus maniculatus

Abstract

Individual variation in maternal care has been shown to have important consequences for offspring behaviour, development, and physiology. The proximate mechanisms associated with these maternal effects have been elegantly detailed in laboratory rodents where environmental variation is typically minimized. However, investigating the ultimate consequences of differences in maternal behaviour and factors that maintain variation in maternal care requires the extension of well established protocols for measuring maternal behaviour in the lab to a wild rodent species. In the present study we build on the important contributions of laboratory research by applying laboratory protocols for quantifying maternal behaviour, maternal provisioning, and maternal responsivity in laboratory rodents to wild-caught Peromyscus, which experience large fluctuations in environmental conditions. We temporarily transported wild-caught deer mice (Peromyscus maniculatus gracilis) to a field laboratory for parturition and the first week post partum and then returned individuals with their offspring to the wild. We demonstrate that the proportion of time spent nursing by wild-caught deer mice was similar to previous studies of laboratory rodents and was repeatable within litters. However, in contrast to prior studies of laboratory rodents, the proportion of time spent nursing by wild-caught deer mice was independent of the proportion of time spent licking and grooming and the latency to retrieve pups in a pup-retrieval test. Wild-caught deer mice also exhibited a high degree of seasonal plasticity in nursing behaviour; females that raised litters early in the season spent almost twice as much time nursing as those raising litters at the end of the season. The amount of time spent nursing offspring in captivity was negatively correlated with population density of wild mice in the field at the time of their capture, but such a seasonal decline in nursing could also be caused by other seasonal changes in their natural environment. These findings suggest the potential for much greater plasticity in maternal care by rodents than might otherwise be revealed from studies of animals born and raised under controlled laboratory conditions.