Lacy Robert C, Alaks Glen, Walsh Allison
Department of Conservation Biology, Daniel F. and Ada L. Rice Center, Brookfield Zoo, Brookfield, Illinois, 60513.
Evolution. 1996 Dec;50(6):2187-2200. doi: 10.1111/j.1558-5646.1996.tb03609.x.
The severity of inbreeding depression appears to vary among taxa, but few ecological or other patterns have been identified that predict accurately which taxa are most sensitive to inbreeding. To examine the causes of heterogeneity in inbreeding depression, the effects of inbreeding on reproduction, survival, and growth were measured in three replicate experimental stocks for each of three subspecies of Peromyscus polionotus mice. Inbreeding of the dam reduced the probability of breeding, the probability of producing a second litter, and litter size. Inbreeding of the litter caused depression of litter size, juvenile viability, and mass at weaning, and caused an increase in the within-litter variance in mass. In spite of differences between the subspecies in natural population sizes, genetic variation, and mean rates of reproduction and survival, all variation observed between experimental populations in their responses to inbreeding could be attributed to random founder effects. The genetic load of deleterious alleles in each replicate was unequally partitioned among its founder pairs, and different founders contributed to the load affecting different fitness components. Thus, inbreeding depression for any one fitness component, in our experimental environment, must be due to relatively few deleterious alleles with major effects. Genetic loads so comprised would be expected to diverge among natural populations due to both random drift and selective removal of recessive deleterious alleles during population bottlenecks. The near universality of inbreeding depression would be maintained, however, if different alleles contribute to inbreeding depression of different fitness components and in different environments.
近亲繁殖衰退的严重程度似乎因分类群而异，但几乎没有能准确预测哪些分类群对近亲繁殖最为敏感的生态或其他模式被识别出来。为了研究近亲繁殖衰退异质性的原因，对鹿鼠三个亚种中的每一个亚种，在三个重复的实验种群中测量了近亲繁殖对繁殖、存活和生长的影响。母本的近亲繁殖降低了繁殖概率、产第二窝的概率以及窝仔数。窝仔的近亲繁殖导致窝仔数减少、幼体活力下降、断奶时体重减轻，并导致窝内体重方差增加。尽管这三个亚种在自然种群大小、遗传变异以及繁殖和存活的平均速率方面存在差异，但在实验种群对近亲繁殖的反应中观察到的所有变异都可归因于随机奠基者效应。每个重复中的有害等位基因的遗传负荷在其奠基者对之间分配不均，并且不同的奠基者对影响不同适合度组分的负荷有贡献。因此，在我们的实验环境中，任何一个适合度组分的近亲繁殖衰退必定是由于相对较少的具有主要效应的有害等位基因所致。由于随机漂变以及在种群瓶颈期间隐性有害等位基因的选择性清除，这样构成的遗传负荷在自然种群中预计会有所不同。然而，如果不同的等位基因在不同的适合度组分以及不同的环境中对近亲繁殖衰退有贡献，那么近亲繁殖衰退的近乎普遍性将得以维持。
