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Should females mate multiply to avoid inbreeding?

The evolution of polyandry, defined as female mating with multiple males within a single reproductive episode, is a major puzzle in evolutionary biology. One hypothesis is that polyandry evolves because it allows females to avoid inbreeding, and thereby avoid decreases in offspring fitness due to inbreeding depression. Yet no formal models have tested this hypothesis given the complex ecological conditions under which polyandry and inbreeding occur in wild populations. We used a computational individual-based modelling approach to quantify the evolutionary dynamics of polyandry and inbreeding while simultaneously tracking internally-consistent distribution of pairwise relatedness between population members. Individuals were modelled with unique genomes underlying propensity for polyandry, and the degree of choice for more or less closely related mates. Replicate simulations were run across different costs of polyandry and inbreeding, and for different constraints on mate availability, allowing us to summarise evolutionary dynamics and emerging patterns of mating. These simulations show that polyandry and inbreeding avoidance can evolve given low direct costs of polyandry and high costs of inbreeding, and when ecological constraints on mate availability and hence initial mate choice are sufficiently strong. However, evolutionary dynamics varied greatly among replicate simulations, reflecting high stochasticity associated with complex ecological conditions enacted within finite populations. Using a computational approach to understand the evolutionary dynamics of complex mating systems therefore advances our understanding of diverse mating behaviours observed in wild populations.

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