Abstract
Post-reproductive lifespan is a common trait among mammals and is usually considered to be neutral; i.e. with no influence on population dynamics. Here, we explore the role of post-reproductive lifespan in the fixation probability of beneficial genetic variation. We compare two separate, stationary populations living in a constant environment that are equivalent except for the average time their respective members spend in the post-reproductive stage of life. Using a recently derived approximation, we show that fixation of a beneficial mutation is more likely in the population with greater post-reproductive longevity. This finding is surprising, as the population with more prolonged post-reproductive lifespan has smaller effective size and the classic population-genetic model would suggest that decreasing effective size reduces fixation chances of beneficial mutations. Yet, as we explain, in the age-structured case, when effective size gets smaller because of longer post-reproductive lifespan but census size is kept equal, a beneficial mutation has a higher likelihood to get fixed because it finds itself at higher initial frequency.
Highlights
In populations with age structure, the fate of genetic variability can be influenced by life history features [1,2,3,4,5,6,7,8,9,10]
The sole exception—which we will not consider in the present work—is when social interactions in the population are postulated to generate correlations between the survival of individuals that are past their last reproductive age and the reproductive success of their still-reproducing relatives
The result we have obtained concerning the relationship between post-reproductive lifespan and the computation of the fixation probability of a beneficial mutation is of interest for the relationship between models with, and models without, age structure
Summary
In populations with age structure, the fate of genetic variability can be influenced by life history features [1,2,3,4,5,6,7,8,9,10]. S should be sufficiently small that there is a negligible difference between the reproductive value of the mutant, VkÃ, and the reproductive value of a resident individual of the same age as the mutant, Vk % Vkà Under these assumptions, Vindenes et al [3] showed that the fixation probability of the mutation, which is initially found as a single copy, is approximately. We use the model with age structure to understand whether fixation is more probable in one of the two populations, A and B, described above To this aim, we first need to understand the effect of post-reproductive lifespan on the demographic variance. Using Eq (5), we can reformulate the demographic variance as
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