Abstract
Population extinction due to the accumulation of deleterious mutations has only been considered to occur at small population sizes, large sexual populations being expected to efficiently purge these mutations. However, little is known about how the mutation load generated by segregating mutations affects population size and, eventually, population extinction. We propose a simple analytical model that takes into account both the demographic and genetic evolution of populations, linking population size, density dependence, the mutation load, and self-fertilisation. Analytical predictions were found to be relatively good predictors of population size and probability of population viability when verified using an explicit individual based stochastic model. We show that initially large populations do not always reach mutation-selection balance and can go extinct due to the accumulation of segregating deleterious mutations. Population survival depends not only on the relative fitness and demographic stochasticity, but also on the interaction between the two. When deleterious mutations are recessive, self-fertilisation affects viability non-monotonically and genomic cold-spots could favour the viability of outcrossing populations.
Highlights
Population size and viability are both affected by extrinsic (e.g. environmental change and interspecific interactions) and intrinsic factors (e.g. genetic and demographic components)
Population size and viability are both affected by extrinsic and intrinsic factors
It is generally accepted that selection is less effective in small populations, which could lead to their extinction due to mutational meltdown [2,3,4,5], whereas large populations are able to purge recurrent deleterious mutations and remain at mutation-selection balance [15,39]
Summary
Population size and viability are both affected by extrinsic (e.g. environmental change and interspecific interactions) and intrinsic factors (e.g. genetic and demographic components). We observe one particular case, when mutations are very tightly linked (the recombination rate D~0:1), of small effect (the coefficient of selection sƒ0:2) and completely recessive (dominance h~0), where increasing the haploid mutation rate U can, for low rates of a0, decrease the probability of extinction and increase the mean relative fitness or have no effect on either (Figures 2A and 2B).
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