Mutant alleles of small effect are primarily responsible for the loss of fitness with slow inbreeding in Drosophila melanogaster

• Published in: Genetics (Austin) 1998-03, Vol.148 (3), p.1143-1158
• Main Author: Latter, B.D.H
• Format: Article
• Language: English
• Subjects: Adaptation, Physiological; Alleles; AMELIORATION DES ANIMAUX; ANIMAL BREEDING; ANIMAL HEALTH; ANIMAL INBREEDING; Animal reproduction; Animals; APLICACIONES DEL ORDENADOR; APPLICATION DES ORDINATEURS; BIOLOGICAL COMPETITION; Chromosome Mapping; COMPETENCIA BIOLOGICA; COMPETITION BIOLOGIQUE; COMPETITIVE ABILITY; COMPUTER APPLICATIONS; COMPUTER SIMULATION; DENSIDAD DE LA POBLACION; DENSITE DE POPULATION; DEPRESION POR CONSANGUINIDAD; DEPRESSION DE CONSANGUINITE; DOMINANCE; DOMINANT GENES; DROSOPHILA MELANOGASTER; Drosophila melanogaster - genetics; Evolution; Female; fitness; FITNESS DECLINE; GENE; GENE DOMINANT; GENE FREQUENCY; GENES; GENES DOMINANTES; Genes, Dominant; Genes, Recessive; Genetic Markers; genetic models; GENETICA; GENETICS; GENETIQUE; HETEROCIGOTOS; HETEROZYGOSITY; HETEROZYGOTE; HETEROZYGOTE SUPERIORITY; HETEROZYGOTES; Inbreeding; INBREEDING DEPRESSION; Insects; LOCI; LOCUS; Male; MEJORAMIENTO ANIMAL; MODELE; MODELOS; Models, Genetic; Mutagenesis; MUTANT; MUTANTES; MUTANTS; Mutation; NATURAL SELECTION; OVERDOMINANCE; PARTIAL DOMINANCE; POPULATION DENSITY; SANIDAD ANIMAL; SANTE ANIMALE; SELECCION NATURAL; SELECTION NATURELLE; SIMULACION; SIMULATION
• ISSN: 0016-6731; 1943-2631; 1943-2631
• DOI: 10.1093/genetics/148.3.1143

Multilocus simulation is used to identify genetic models that can account for the observed rates of inbreeding and fitness decline in laboratory populations of Drosophila melanogaster. The experimental populations were maintained under crowded conditions for approximately 200 generations at a harmonic mean population size of Nh approximately 65-70. With a simulated population size of N = 50, and a mean selective disadvantage of homozygotes at individual loci approximately 1-2% or less, it is demonstrated that the mean effective population size over a 200-generation period may be considerably greater than N, with a ratio matching the experimental estimate of Ne/Nh approximately 1.4. The buildup of associative overdominance at electrophoretic marker loci is largely responsible for the stability of gene frequencies and the observed reduction in the rate of inbreeding, with apparent selection coefficients in favor of the heterozygote at neutral marker loci increasing rapidly over the first N generations of inbreeding to values approximately 5-10%. The observed decline in fitness under competitive conditions in populations of size approximately 50 in D. melanogaster therefore primarily results from mutant alleles with mean effects on fitness as homozygotes of sm < or = 0.02. Models with deleterious recessive mutants at the background loci require that the mean selection coefficient against heterozygotes is at most hsm approximately 0.002, with a minimum mutation rate for a single Drosophila autosome 100 cM in length estimated to be in the range 0.05-0.25, assuming an exponential distribution of s. A typical chromosome would be expected to carry at least 100-200 such mutant alleles contributing to the decline in competitive fitness with slow inbreeding.