EVORA

Reproductive ageing - the decrease in reproductive performance with increasing age - is a pervasive biological process associated with profound biological, demographic and social implications. Yet, a comprehensive understanding of the causes and consequences of reproductive ageing remains particularly elusive. This knowledge gap is mostly due to the fact that a thorough understanding of the ageing process requires fully embracing the interplay between male and female reproductive ageing. However, the overwhelming majority of studies that have investigated this process through the lens of evolutionary biology have focused on females. The aim of the EVORA project is to obtain an integrative understanding of the evolutionary causes of male reproductive ageing and its consequences for females, at different levels of the biological organisation and in various environmental conditions. First, we will perform a thorough literature survey to compile sex- and age-specific reproductive data across mammals. We will then quantify the diversity of reproductive ageing patterns by estimating for each species (and each reproductive traits) the age at the onset of reproductive ageing and the rate of reproductive ageing. We will then determine the ecological and life-history factors that influence the occurrence of reproductive ageing and shape the diversity of observed patterns in both sexes, using phylogenetically-controlled comparative analyses. Second, we will dissect the evolutionary causes of male reproductive ageing in two not-hunted and enclosed wild populations of roe deer (Capreolus capreolus). These two populations show contrasted environmental conditions and individuals from these two populations have been monitored individually for more than 40 years. We will organize summer capture to collect novel data on pre-copulatory traits (e.g. scent gland secretions, antler’s morphology) and post-copulatory traits (e.g. sperm quantity and quality) that we will further analyse in order to obtain the age-specific trajectories of each trait. Then we will test predictions from evolutionary theories of ageing, by investigating whether a strong allocation to growth and reproduction in early adulthood is associated to an earlier and/or steeper reproductive ageing in males. In addition, we will explore whether these associations are modulated by the environmental conditions and mediated by a decreased in somatic condition (assessed by various biological markers of ageing, e.g. epigenetic age, telomere length). Third, we will identify the evolutionary consequences of male reproductive ageing for female in roe deer. In a first step, we will quantify the fitness costs of mating with old males for females by analysing the effect of male chronological age on fawn health and survival, while controlling for mother age and condition. This will be possible thanks to the detailed pedigree of the two populations. In a second step, we will investigate the possible counter-adaptations that have evolved in females to buffer the fitness costs of male reproductive ageing. Here, we will take advantage of captive female’s roe deer from an experimental station to test whether females can discriminate males on the basis of either their chronological age and biological age through olfactory communication (using scent gland secretions collected on males from the two wild populations) thanks to mate-preference experimental design. Based on a unique combination of life-history, behavioural, physiological and genetic data for both sexes, the EVORA project will go beyond classical reproductive ageing studies and will generate a thorough understanding of the sex-specific evolutionary causes and consequences of the reproductive ageing process. The focus on roe deer, a long-lived mammal living in free-ranging conditions, will widen the scope of EVORA by providing novel insights for both evolutionary biology and biogerontology.