Ontogeny of thermoregulation in the Djungarian hamster (Phodopus campbelli).

At birth, altricial Djungarian hamster pups require exogenous heat to grow and gain little benefit from huddling with their littermates. By day 6 huddled pups begin effective thermogenesis although isolated pups do not show spontaneous increases in temperature until day 9. On day 12, isolated pups can resist cooling for short periods of time and huddles do not cool within a 15 min test. By day 15, isolated pups can thermoregulate, although at a lower core body temperature than is typical of adults, and both huddling contact with littermates and direct contact with the dam are reduced. At weaning, pups are effectively thermally independent. This ontogeny is correlated with behavioral, morphological and physiological changes during pup development including brown adipose tissue (BAT) thermogenesis, pelage development and body size. The onset of thermogenesis, and then thermoregulation, causes temporary reductions in pup growth rate on days 6 and 7 and again on days 12 and 13. Body weight, rather than pup age, appears critical for independent thermoregulation. These results are discussed relative to the extent of maternal hyperthermia and the physiological demands of the concurrent gestation characteristic of reproduction in Djungarian hamsters.