Behavioral and physiological responses of female house mice to foraging variation

Peripubertal female house mice were required to work for their food at either 23 degrees C or 9 degrees C. We used a special caging system in which animals had to emerge from a thermally-buffered burrow and run a programmable number of running wheel revolutions to obtain a pellet of food. Of concern here were the behavioral and physiological adjustments necessary to accommodate growth and reproductive development when faced with the need to forage for different lengths of time at different temperatures. When female house mice are confronted with poor foraging at cool temperatures they allot their highest priorities to maintaining energy balance; body growth is next, and reproductive development and nonforaging activity have the lowest priorities. Our results also demonstrate that the time spent foraging while exposed to low ambient temperature is critical for this species. This relationship probably determines whether or not house mice will breed continuously or seasonally in a particular habitat.