All mammals share a fundamental energy-related concern: once the initial costs of obtaining and assimilating food energy have been accomplished, then remaining surplus energy must be allocated parsimoniously among a variety of competing physiological and behavioral demands. Obtaining food to meet survival demands is a core energetic constraint to which most other dimensions of development, such as growth and especially reproduction, must be subservient. Because of the disparate demands of reproduction between the two sexes, they can often be conceptually treated as separate species. It is therefore not surprising that males and females of certain species have evolved markedly different priorities for energy allocation. Dr. Glenn Perrigo is making use of the mouse as an experimental model to investigate differences in energy allocation strategies between males and females. His work will examine organizational and activational effects of early gonadal hormones on sex differences. He will also study effects of maternal stress on the fetal hormone milieu of offspring whose mothers are subject to rigorous foraging conditions during pregnancy. This work should give us more information on how gonadal hormones effect differences in energy allocation in mammals.