Inbreeding depression drives evolution of dispersal and polyandry

Inbreeding depression, defined as the reduction in fitness components of offspring of related individuals compared to offspring of unrelated individuals, is a widespread phenomenon and has profound demographic and evolutionary consequences. It can reduce the mean fitness of a population and increase extinction risk, and it can affect traits evolution. Inbreeding depression is widely hypothesized to be a key driver of the evolution of, among other traits, dispersal (individual movements potentially leading to spatial gene flow) and polyandry (female mating with multiple males within a single reproductive bout), as mechanisms to avoid inbreeding. In turn, both dispersal and polyandry can change the relatedness structure within and among populations, thus affecting opportunity for inbreeding and consequent evolution of inbreeding depression. However, despite this potential major shared driver, and despite the large amount of both theoretical and empirical work, evolution of dispersal and polyandry given inbreeding have been so far studied separately, and thus we still do not know whether and how dispersal and polyandry affect each other9s evolution, and how they may feed-back onto evolution of inbreeding depression itself. Here, using a genetically-explicit individual-based model, which models realistic distributions of selection and dominance coefficients of deleterious recessive mutations underpinning inbreeding depression, I show that: 1) inbreeding depression indeed drives evolution of dispersal and polyandry; 2) there is a negative feedback between dispersal evolution and polyandry evolution, which therefore evolve as alternative inbreeding avoidance strategies; 3) inbreeding depression is mainly shaped by the level of dispersal, while polyandry has a much more limited effect.