Explaining sex differences in lifespan in terms of optimal energy allocation in the baboon

Abstract

We provide a quantitative test of the hypothesis that sex role specialization may account for sex differences in lifespan in baboons if such specialization causes the dependency of fitness upon longevity, and consequently the optimal resolution to an energetic trade-off between somatic maintenance and other physiological functions, to differ between males and females. We present a model in which females provide all offspring care and males compete for access to reproductive females and in which the partitioning of available energy between the competing fitness-enhancing functions of growth, maintenance, and reproduction is modeled as a dynamic behavioral game, with the optimal decision for each individual depending upon his/her state and the behavior of other members of the population. Our model replicates the sexual dimorphism in body size and sex differences in longevity and reproductive scheduling seen in natural populations of baboons. We show that this outcome is generally robust to perturbations in model parameters, an important finding given that the same behavior is seen across multiple populations and species in the wild. This supports the idea that sex differences in longevity result from differences in the value of somatic maintenance relative to other fitness-enhancing functions in keeping with the disposable soma theory.

Faecal parasites increase with age but not reproductive effort in wild female chimpanzees

“…This accumulated burden of reproduction may be particularly challenging for female apes who invest heavily in singleton offspring requiring years of care, and whose reproductive success is dependent on survival to old age [5]. Alternatively, the selection of females may compensate for slow reproductive rates by increasing investments in immune defence that promote survival and future reproduction [6–8]. Despite the straightforward predictions, the extent to which cumulative reproductive effort impacts variation in health and ageing within and among wild ape species is unknown.…”

Insights from evolutionarily relevant models for human ageing

“…Genomic studies indicate that the mechanisms which are the focus of research in conventional model organisms, like worms, flies and rodents, have not been major targets of selection in humans and are unlikely to explain interspecific variation in longevity among primates [48]. The combination of a long life and extensive parental investment has shaped primate life course strategies [49,50], potentially affecting not only how quickly we age but also how we age. Primates are indispensable for examining aspects of cognitive, neurobiological and social ageing that are simply not captured in existing animal models.…”

Mitonuclear effects on sex ratio persist across generations in interpopulation hybrids

“…Because interactions between the products of mitochondrial DNA (mtDNA) and nuclear DNA (nDNA) are central to metabolism, these mitonuclear interactions might be expected to have different effects in males and females, who often have quite different metabolic demands 5,6,7 . Indeed, even if the two sexes have equivalent metabolic rates, they may have dramatically different energy allocations to different tissue types or life history components 8,9,10 . Selection on mtDNA may also be sex-biased due to the asymmetrical inheritance of mtDNA.…”