• conservation;
  • extinction;
  • inbreeding depression;
  • mutation accumulation;
  • reproduction;
  • stochasticity

Despite strong empirical evidence of the harmful effects of inbreeding on fecundity, spontaneous recessive deleterious mutations are generally considered as acting on survival only in evolutionary models and population viability analyses. In this study, we modelled a species with separate sexes to assess the effect of selection on fecundity in small populations on the risk of extinction. We showed that the impact of inbreeding on short-term fitness changes and that population dynamics are strongly influenced by phenotypic interactions among males and females during reproduction. In particular, population persistence was found to be highly sensitive to the level at which selection acts (i.e. individual vs. pair) and to asymmetry among sexes (in terms of mutation rates and mutational effects). © 2005 The Linnean Society of London, Biological Journal of the Linnean Society, 2005, 86, 467–476.