Thermal constraints on maternal behavior during reproduction in dwarf hamsters (Phodopus).

The chronic hyperthermia of lactating dwarf hamster (Phodopus) dams may constrain maternal behavior if contact with the litter further increases their body temperature, forcing the termination of nest bouts to dissipate the heat load. Changes in female body temperature and nest attendance in two species of dwarf hamster (P. campbelli and P. sungorus) were recorded each minute over the reproductive cycle. As the pups develop from naked poikilotherms to well-insulated thermoregulators, they function as heat sinks and heat sources. This role of pup development in maternal thermoregulation interacts with the dam's activity, primarily nocturnal wheel running, to produce a complex pattern of heating and cooling in each species. Contact with the pups is more constrained by maternal temperature during the inactive phase (day), and more constrained in P. campbelli than in P. sungorus. The interspecific difference in pup development or maternal thermoregulation is consistent with predictions based on biparental care, and a thermoregulatory role for the male in P. campbelli, but not in P. sungorus. These data suggest that environmental temperature and water availability are ecological variables that affect maternal thermoregulation, reproductive success, and the need for biparental care.