Whitlock M C
Department of Zoology, University of British Columbia, Vancouver, Canada.
Evolution. 2000 Dec;54(6):1855-61. doi: 10.1111/j.0014-3820.2000.tb01232.x.
With a small effective population size, random genetic drift is more important than selection in determining the fate of new alleles. Small populations therefore accumulate deleterious mutations. Left unchecked, the effect of these fixed alleles is to reduce the reproductive capacity of a species, eventually to the point of extinction. New beneficial mutations, if fixed by selection, can restore some of this lost fitness. This paper derives the overall change in fitness due to fixation of new deleterious and beneficial alleles, as a function of the distribution of effects of new mutations and the effective population size. There is a critical effective size below which a population will on average decline in fitness, but above which beneficial mutations allow the population to persist. With reasonable estimates of the relevant parameters, this critical effective size is likely to be a few hundred. Furthermore, sexual selection can act to reduce the fixation probability of deleterious new mutations and increase the probability of fixing new beneficial mutations. Sexual selection can therefore reduce the risk of extinction of small populations.
在有效种群规模较小的情况下，随机遗传漂变在决定新等位基因的命运方面比选择更为重要。因此，小种群会积累有害突变。如果不加以控制，这些固定等位基因的影响会降低物种的繁殖能力，最终导致灭绝。新的有益突变若通过选择得以固定，则可以恢复部分损失的适应性。本文推导了由于新的有害和有益等位基因固定而导致的适应性总体变化，该变化是新突变效应分布和有效种群规模的函数。存在一个临界有效规模，低于此规模种群的适应性平均会下降，但高于此规模时有益突变可使种群持续存在。根据相关参数的合理估计，这个临界有效规模可能为几百。此外，性选择可以降低有害新突变的固定概率，并增加有益新突变的固定概率。因此，性选择可以降低小种群灭绝的风险。
