Fig. 1. Development of wheel-running activity (revs day^–1 and km day^–1), energy intake (kJ day^–1) and whole body mass (g) of females mice facing low foraging costs (L; filled circles), high foraging costs (H; open circles) and restricted feeding without foraging effort (R; gray shading). Error bars show the standard error of the mean. Temperature transmitters were surgically implanted (S) on day –34±1. L and H females were placed in cages with running wheels on day –27 and exposed to the foraging task on day 0. Food rationing of R females also began on day 0. Foraging costs of H mice increased by 10% of baseline every other day until day 20 and were then held constant (at 200% baseline). Animals were injected with the novel antigen KLH on day 39±1 and sacrificed on day 49±1. Energy intake is based on grams of food ingested and manufacturer's estimate of energy content of food (line 3 of Table 1). Sample sizes per group were L=8, H=6 and R=7.