Lability of fat stores in peripubertal wild house mice.

Traditionally, the adaptive value of mammalian white fat stores is considered in relation to long-term needs such as providing protection against the vagaries of winter or signalling the reproductive system when energy reserves are sufficient to risk pregnancy. As shown here, the fat stores of young house mice could not serve such needs. Despite prolonged acclimation and excess nesting material, food deprivation at 10 degrees C significantly lowered the fat stores of peripubertal female house mice in only 12 h, and would exhaust them in 30 h. Even close to thermoneutrality (24 degrees C) the calculated time to exhaustion was only 70 h. The fat stores of a young house mouse are obviously too meager to offer any meaningful protection over a winter of several months duration, or even over a 5-6-week cycle of pregnancy and lactation. Furthermore, in a wild habitat where food availability and ambient temperature can vary rapidly and greatly, such fat stores would be too labile to effectively coordinate puberty with somatic development.