Proximate and ultimate drivers of an unusual adult sex ratio in redfronted lemurs (Eulemur rufifrons)

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In most mammalian species, including humans, males and females exhibit differences in age-specific survival, usually resulting in female-biased adult sex ratios (ASR). Data on age and sex-related variation in health and survival can reveal fundamental sex differences in biological adaptations, but such data are extremely scarce for wild populations and unavailable for species with unusually biased ASRs. The main objectives of our proposed study are therefore (i) to determine age- and sex-specific survival patterns for a wild population of redfronted lemurs with male-biased ASR, to assess (ii) age- and sex-specific variation in determinants of health and survival, as well as (iii) mechanisms that contribute to survival to understand the patterns and dynamics of their sex ratios from birth to death. To achieve these objectives, we will combine three data sets, i.e., long-term demographic data, hormonal, genetic and behavioral data from previous studies, and new physiological and behavioral data. By examining sex- and age-related variation in survival, immunocompetence, parasitism, frailty, social buffering and risk-taking, our study will be among the first to investigate the adaptive significance and proximate mechanisms underlying sex differences in health and survival in a wild primate population. As such, it will also contribute comparative perspectives for a better understanding of the human male-female health-survival paradox as well as constitute one of the most comprehensive analyses of the drivers of sex ratio variation across the lifespan in wild mammals.