Par Julie LANDES, doctorante de l’équipe BIOADAPT, UMR 7179 MECADEV - Mécanismes adaptatifs et Evolution, et l’équipe Génétique des Populations, UMR 7206 Eco-anthropologie et Ethnobiologie

Would organisms age faster if their pace of life was accelerated? Species’ lifespan are widely explained by their pace of life, reflecting the fact that species differ in their amount of metabolic activity per unit of time. Within a given species however, the effect of inter-individual variations in speed of life on mortality patterns is still poorly understood. Several studies showed that a decreased metabolic activity leads to an enhanced lifespan. However, the extent to which metabolic restriction mimics a reduction in the pace of life and influences the speed at which mortality increases with age is unknown.The grey mouse lemur Microcebus murinus is a seasonal heterothermic primate experiencing drastic reductions of basal metabolism during the unfavorable season. Manipulating the seasonal succession rhythm of this species allows a manipulation of the individual metabolic activity over time. We experimentally accelerated the seasonal rhythm of 328 individuals inducing faster fluctuations in their basal metabolism, but maintaining everything else constant (e.g. food availability, temperature). The mortality changes with age of the accelerated lemurs were compared to 1228 control individuals using both semi-parametric and parametric survival analyses. This allowed us characterizing the Weibull-shaped baseline mortality hazard of the grey mouse lemurs. We then analyzed the effect of an accelerated seasonal rhythm on the lemurs’ increase in mortality with age to test whether aging patterns are best explained by chronological age (i.e. the number of lived years) or the number of lived seasons. Our results show that accelerated seasonal rhythm leads to accelerated aging: individuals experiencing two seasonal cycles per year instead of one exhibit similar mortality levels than control individuals twice their age. Furthermore this is the number of shifts between the seasons that shapes mortality rather than age per se. Further studies will investigate the physiological mechanisms underlying this aging pattern variation.