Sex Differences in the Energy Allocation Strategies of House Mice

Sex differences in energy allocation were studied in wild stock house mice (Mus domesticus). Peripubertal animals of both sexes, either intact or gonadectomized, were subjected for 8 weeks to one of two feeding requirements by using a caging system in which a pellet dispenser was controlled by activity on a running wheel. Recently weaned animals were required to run 200 vs 300 or more wheel revolutions to obtain a pellet of food. The 200 revolution requirement allowed normal body growth and reproductive development; the 300+ requirement was adjusted weekly to maintain food intake at a level that allowed survival but did not permit normal body growth. Reproductive development was completely inhibited in intact females at 300+ revolutions whereas intact males at 300+ revolutions, despite stunted growth, all experienced normal sexual development. At both feeding requirements, however, females exhibited more total locomotor activity and consumed more food than males, regardless of gonadectomy. Furthermore, at the 200 revolution requirement we often observed extensive running activity beyond that needed to generate the amount of food actually eaten, especially among females. This "extra" locomotor activity was gonad-dependent in males, but not so in females. These results suggest that male and female house mice employ different strategies when relating their behavior and reproductive development to existing foraging conditions. Females appear more resource-dependent than males.