Genet. Sel. Evol. 38 (2006) 371-387
DOI: 10.1051/gse:2006010

On the expected relationship between inbreeding, fitness, and extinction

Konstantinos Theodorou^a and Denis Couvet<sup>b

a</sup>  Biodiversity Conservation Laboratory, Department of Environmental Studies, University of the Aegean, University Hill, 81100 Mytilene, Greece
^b  CRBPO, Muséum National d'Histoire Naturelle, 55, rue Buffon, 75005 Paris, France

(Received 4 August 2005; accepted 17 January 2006; published online 23 June 2006)

Abstract - We assessed the expected relationship between the level and the cost of inbreeding, measured either in terms of fitness, inbreeding depression or probability of extinction. First, we show that the assumption of frequent, slightly deleterious mutations do agree with observations and experiments, on the contrary to the assumption of few, moderately deleterious mutations. For the same inbreeding coefficient, populations can greatly differ in fitness according to the following: (i) population size; larger populations show higher fitness (ii) the history of population size; in a population that recovers after a bottleneck, higher inbreeding can lead to higher fitness and (iii) population demography; population growth rate and carrying capacity determine the relationship between inbreeding and extinction. With regards to the relationship between inbreeding depression and inbreeding coefficient, the population size that minimizes inbreeding depression depends on the level of inbreeding: inbreeding depression can even decrease when population size increases. It is therefore clear that to infer the costs of inbreeding, one must know both the history of inbreeding (e.g. past bottlenecks) and population demography.

Key words: inbreeding / extinction / conservation / genetic load / deleterious mutation

Correspondence and reprints: ktheo@aegean.gr

© INRA, EDP Sciences 2006