Tolerant versus sensitive genomes: The impact of deleterious mutation on fitness and conservation

Abstract

Using two alternative mutational models, Iinvestigate equilibrium diffusion predictionsfor population fitness. In the classical``sensitive model'', fitness is highly sensitiveto mutations, these usually having mildlydetrimental effects. In the ``tolerant model'',most mutations have only tiny deleteriouseffects, but a small proportion is considerablydetrimental. When the same relationship betweenthe degree of dominance and the homozygousdeleterious effect of mutations is assumed,both models predict important inbreedingdepression after bottlenecking in largepopulations, although the sensitive oneaccounts for a higher average degree ofdominance. Under the sensitive model, the rateof fitness decline due to deleterious fixationis large for effective population sizes in the tens, and could be important in thelong term for effective sizes about 100, inagreement with previously published results.This suggests that conservation programs shouldact to avoid mutational meltdown. Under thetolerant model, however, the fitness declinedue to deleterious fixation is generally low,indicating that conservation programs shouldgive priority to avoid quick inbreeding, lossof genetic variability and adaptation tocaptive conditions, even if this reduces thestrength of selection against new mutations.