The effect of the timing of selection on the mutation load, inbreeding depression and population size

Diala Abu Awad (1) , Sylvain Billiard (1) , Viet Chi Tran (2)

1 GEPV - Génétique et évolution des populations végétales
2 LPP - Laboratoire Paul Painlevé - UMR 8524

If and how the genetic load affects population size has been long debated as on one hand it has been suggested that a high genetic load leads to extinction, and on the other hand, if selection during the life-cycle takes place before density dependence has acted, then population size should not be affected by its genetic load. Explicitly considering the life cycle and the timing of selection is therefore a factor that cannot be ignored when quantifying the effect of deleterious mutations on population size. In addition, population genetics models calculating the expected genetic loads and levels of inbreeding depression ignore the potential effects of demography on these variables. Here we propose a deterministic model in continuous time where deleterious mutations affect individual fitness in one of four ways: by decreasing mating success, fecundity and adult or zygote survival. The genetic load, inbreeding depression and population size are variables that emerge from the model. Our results are compared to the expectations from the fundamental model of natural selection. We find that changing the timing of selection mostly affects population size, but also leads to genetic loads and inbreeding depression that diverge from the fundamental model. Our results emphasize the importance of integrating both population demography and genetics in order to study the demographic impact and, more generally, the fate of deleterious mutations.

Mots clés: Genetic load; Population size; Inbreeding depression; Selection; Deleterious mutations; Demography

Domaines: Evolution [q-bio.PE]

Diala Abu Awad, Sylvain Billiard, Viet Chi Tran. The effect of the timing of selection on the mutation load, inbreeding depression and population size. 2014. ⟨hal-00987288v2⟩