deleterious mutation
Ávila V & García-Dorado A 2002 The effects of spontaneous mutation on competitive fitness in Drosophila melanogaster. J Evol Biol 15:561-565.
- the rate of mean log-fitness decline and that of increase of the between-line variance were consistent with a low rate (λ ≈ 0.03 per gamete and generation), and moderate average fitness effect [E(s) ≈ 0.1] of deleterious mutation
- MA recombinant chromosomes quickly recovered to about the average fitness level of control chromosomes
- thus, deleterious mutations responsible for the fitness decline were efficiently selected against in relatively small populations
- confirming that their effects were larger than a few percent
- because of partial recessiveness of deleterious effects, the main short-term threat for a large population is concealed in the heterozygous condition, and will only become manifest because of increased homozygosity after bottlenecks
- this is usually measured as the rate of inbreeding depression
- which depends on the rate, effect and degree of heterozygous expression of deleterious mutations
- for populations maintained at small sizes during long periods, the main threat might arise from fixation of new deleterious mutations (Lynch et al., 1995)
- the fixation probability depends on the relationship between the homozygous deleterious effect (s) and the effective population size (Ne)
- in classical experiments (e.g. Mukai et al., 1972) large rates of mean viability decline (ΔM ≈ 0.01 per generation) were ascribed to MA
- resulting in a high estimate of the mutation rate (λ > 0.3 per gamete and generation) with mild deleterious effect [average deleterious homozygotic effect E(s) < 0.03]
- more recent experiments and reanalysis of older ones detected smaller rates of decline (ΔM ≈ 0.002), giving low rates of viability deleterious mutation (λ ≈ 0.01) with moderate average effect [E(s) ≈ 0.1]
- using the minimum distance (MD) method unconditional to the observed fitness decline gave ΔM ≈ 0.008, λ ≈ 0.03, E(s) ≈ 0.26 for relative fitness (García-Dorado et al., 1998)
- these rate and effects are somewhat larger than those obtained for viability in recent results and reanalysis
- this is to be expected, as some mutations can reduce fitness without reducing viability
- mutations reducing viability may also have deleterious effects on other fitness components
- ΔM ≈ 0.002, λ ≈ 0.015, E(s) ≈ 0.10 have been reported at generation 105 for noncompetitive viability (García-Dorado et al., 1998)
- ΔM ≈ 0.002, λ ≈ 0.03, E(s) ≈ 0.08 for competitive viability at generation 250 (Chavarrías et al., 2001; chromosome II results adjusted for the whole haploid genome)