Influences of photoperiod and ambient temperature on maternal-pup interactions in the meadow vole (Microtus pennsylvanicus).

Abstract

Seven experiments were used to assess nesting time in meadow voles (Microtus pennsylvanicus) raising offspring in conditions designed to mimic the spring, fall and winter seasons. Prenatal exposure to the maternal photoperiod serves as a signal for the onset of physiological changes in the meadow vole in preparation for the environmental conditions following birth. Meadow vole pups born in short days (LD 10:14; SD) grow at a slower rate and have longer and denser pelage by 21 days postpartum than those born in long days (LD 14:10; LD). Differences in growth rate may, in part, be related to the amount of time the dam is in contact with her litter. Previous studies with other species have correlated the dam's time in the nest with nest temperature. I predicted that short day (SD) dams would spend less time in contact with their pups as a consequence of the enhanced capacity of the pups to thermoregulate. Experimental conditions included variations in daylength and in ambient temperature, with pups being raised in warm (22$\sp\circ$C) or cold (8$\sp\circ$C) temperatures. The results revealed that dams in the summer and winter conditions spent significantly more time in the nest with their pups than those in the fall condition. Nesting time also increased significantly for animals in the cold ambient temperature in all photoperiod conditions. These differences were somewhat related to thermoregulatory abilities in the pups as measured by pelage development, tail and body length and nest temperature of the litters. Nest temperature was higher for LD than for SD pups when dams were either on or off of the nest. LD dams remain in the nest longer and spend shorter periods off of the nest than SD dams to maintain this higher temperature. The dam's behavior appears to be the critical factor in the regulation of nest temperature, as her time on the nest determines the level at which the temperature is maintained.