Competition and cooperation among huddling infant rats

Huddling is expressed by infant rats and continues to be an important behav ior throughout adulthood. As a form of behavioral thermoregulation, huddlin g is thought to play all essential role in compensating for inadequate phys iological thermoregulation early in development. Infant rats, however are c apable of heat production shortly after birth using brown adipose tissue (B AT) and exhibit thermogenesis in the huddle, suggesting that huddling does not obviate the need for endothermy during cold exposure. In the present ex periment, 4-pup huddles of infant rats (2- or 8-day-olds) were exposed to t wo subthermoneutral temperatures, and BAT thermogenesis was inhibited in 0, 2, or 4 of the rats' in each huddle. Inhibition of BAT thermogenesis compr omised the pups' ability to maintain huddle temperature, but surprisingly d id not result in enhanced huddling at either age. These results suggest tha t effective huddling during cold exposure requires the thermal resources pr ovided by endothermy. Furthermore, the heat provided by BAT appears to shap e behavioral interactions in the huddle during development. (C) 2001 John W iley & Sons, Inc.