Assessing the impact of realized relatedness on primate sociality using whole genome sequencing

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Rapid technological advances such as whole genome sequencing (WGS) have opened up exciting new avenues for genomic studies in a wide range of species. One of the topics that will be substantially impacted by this progress is the influence of kin-driven behaviour on social relationships, which are of crucial importance for health and fitness even in humans. As predicted by kin selection theory, individuals in many taxa frequently bias their social behaviour towards conspecifics depending upon the proportion of alleles shared. Yet the observed patterns are highly variable, which may be due to imprecise estimates of genetic relatedness.Measuring social preferences for (e.g. nepotism) and against kin (e.g. inbreeding avoidance) requires accurate estimates of relatedness (or identity-by-descent, IBD). Notably, the amount of the genome shared by relatives varies considerably due to stochastic processes during meiosis, resulting in a gradient of IBD values that is only poorly reflected by relatedness estimates from previously used methods. Pedigrees or Short Tandem Repeat (STR) markers, for instance, provide either categorical averages or rather imprecise estimates based on parts of the genome. WGS, on the other hand, assays all single-nucleotide variants across the entire genome, thus providing the most authoritative relatedness estimates and unprecedented power for addressing questions on kin-driven behaviour. Primate relatedness has so far mainly been examined at the categorical level but not along a gradient in IBD. This leaves major gaps in our understanding of sociality and its evolution. WGS data on free-ranging primates remain scarce, but are imperative to fill these gaps. Here we will take advantage of an exceptional population of free-ranging rhesus macaques (Macaca mulatta) at Cayo Santiago (Puerto Rico), for which demographic, reproductive, behavioural, and other phenotypic data have been collected over decades. We will link these data with IBD from WGS in 800 animals to assess the impact of the gradient in IBD on social preferences for and against kin. With this integrative approach, we will pursue three main aims: 1. We will quantify variation in IBD within and between kin classes and will compare differences between IBD estimates from WGS data, pedigrees and STR markers. 2. We will determine whether social preferences are predicted by the gradient in IBD. To understand the mechanisms of kin bias, we will relate phenotypic similarities to variation in IBD and assess whether phenotypic cues are perceived according to shared IBD. 3. We will investigate whether inbreeding and inbreeding depression can be detected from WGS data, and whether shared IBD affects individual mating preferences and breeding. By combining IBD from WGS with extensive social data on a large set of individuals, the project will contribute significantly to unravelling the impact of realized relatedness on sociality in our evolutionary history.