Willis J H
Department of Biology, University of Oregon, Eugene, OR 97403, USA.
Heredity (Edinb). 1999 Sep;83 ( Pt 3):337-46. doi: 10.1038/sj.hdy.6885790.
The magnitude of inbreeding depression can influence many aspects of a population's ecology and evolution, including the nature of selection acting on the mating system and the chances that the population will go extinct during periods of small population size. If inbreeding depression is caused primarily by recessive mutations of large effect on fitness, such as lethals or steriles, then it is expected to be purged rapidly by selection with moderate amounts of inbreeding. In contrast, inbreeding depression primarily caused by many genes with mild effects on fitness will not be rapidly purged with inbreeding, so it should be a more resilient barrier to the evolution of self-fertilization and a more significant threat to the survival of endangered species. Here I show that recessive male-sterility alleles at individual loci are common in a primarily outcrossing population of the plant Mimulus guttatus. Despite the high frequency of these major mutations, most of the inbreeding depression for male fertility and cumulative measures of lifetime fitness results from more mildly deleterious alleles. Male-sterility alleles contribute to 31% of the inbreeding depression for the fraction of viable pollen grains, and to 26% of the inbreeding depression for total fitness. These results suggest that most of the inbreeding depression for male fertility in this population would not be purged, in the short term, with moderate inbreeding.
近亲繁殖衰退的程度会影响种群生态与进化的诸多方面，包括作用于交配系统的选择性质以及种群在小种群规模时期灭绝的可能性。如果近亲繁殖衰退主要由对适合度有重大影响的隐性突变引起，比如致死或不育突变，那么预计通过适度近亲繁殖的选择会迅速清除这些突变。相反，主要由许多对适合度有轻微影响的基因导致的近亲繁殖衰退不会因近亲繁殖而迅速清除，所以它应该是自花受精进化的更具韧性的障碍，也是对濒危物种生存的更重大威胁。在此我表明，在主要进行异交的沟酸浆属植物种群中，单个位点的隐性雄性不育等位基因很常见。尽管这些主要突变的频率很高，但雄性育性的近亲繁殖衰退以及终生适合度的累积测量结果大多源于危害程度更轻的等位基因。雄性不育等位基因对可育花粉粒比例的近亲繁殖衰退贡献了31%，对总适合度的近亲繁殖衰退贡献了26%。这些结果表明，短期内，适度近亲繁殖不会清除该种群中雄性育性的大部分近亲繁殖衰退。
