Metabolic Strategy and Social Behavior in Lemuridae

Abstract

Research on lemurs contributes importantly to evaluation of hypotheses on primate development and evolution. A central question about social behavior has asked why adult females in many lemur species socially dominate males while this trait is rare among Anthropoids and other mammals. At present, the favored hypothesis-that female lemurs undertake unusually costly reproduction and dominance over males is necessary for females to access sufficient nutrition throughout Madagascar's dry season-has both supporters and detractors. We propose that confusion concerning female dominance in lemurs derives from failing to appreciate that adaptation should have minimized prospects for seasonal stress and that success during months of food abundance. not months of food scarcity, is most likely to be the primary foraging factor influencing relative fitness among today's lemurs. Analyses of hair growth, somatic growth, food intake, fatness, and two metabolically-active hormones (thyroxine and insulin-like growth factor 1) revealed that Lemur catta and Eulemur fulvus rufus prepare during the photoperiod of Madagascar's annual wet season for upcoming dry seasons and also make adjustments during dry seasons that make life less expensive. Phenological data from three Malagasy ecosystems suggest that seasonal changes in fruit availability may be a less important selection pressure in the evolution of lemur life histories than previously thought, whereas changes in availabilities of leaves and flowers might be crucial. Detailed new fieldwork in nutritional ecology will be required to evaluate this hypothesis and also to help determine why Eulemur fulvus does not show female dominance. ideally, such work would be accompanied by information on metabolic physiology, reproduction, and social behavior from a variety of lemurs. More generally, increased research on metabolic strategies in primates and other mammals would contribute as much to illuminating adaptive patterns of behavior as has research on sexual selection and mating strategies to date.