Lacy Robert C, Ballou Jonathan D
Department of Conservation Biology, Daniel F. and Ada L. Rice Center, Chicago Zoological Society, Brookfield, Illinois, 60513.
Department of Zoological Research, National Zoological Park, Smithsonian Institution, Washington, D.C., 20008.
Evolution. 1998 Jun;52(3):900-909. doi: 10.1111/j.1558-5646.1998.tb03715.x.
It has been hypothesized that natural selection reduces the "genetic load" of deleterious alleles from populations that inbreed during bottlenecks, thereby ameliorating impacts of future inbreeding. We tested the efficiency with which natural selection purges deleterious alleles from three subspecies of Peromyscus polionotus during 10 generations of laboratory inbreeding by monitoring pairing success, litter size, viability, and growth in 3604 litters produced from 3058 pairs. In P. p. subgriseus, there was no reduction across generations in inbreeding depression in any of the fitness components. Strongly deleterious recessive alleles may have been removed previously during episodes of local inbreeding in the wild, and the residual genetic load in this population was not further reduced by selection in the lab. In P. p. rhoadsi, four of seven fitness components did show a reduction of the genetic load with continued inbreeding. The average reduction in the genetic load was as expected if inbreeding depression in this population is caused by highly deleterious recessive alleles that are efficiently removed by selection. For P. p. leucocephalus a population that experiences periodic bottlenecks in the wild, the effect of further inbreeding in the laboratory was to exacerbate rather than reduce the genetic load. Recessive deleterious alleles may have been removed from this population during repeated bottlenecks in the wild; the population may be close to a threshold level of heterozygosity below which fitness declines rapidly. Thus, the effects of selection on inbreeding depression varied substantially among populations, perhaps due to different histories of inbreeding and selection.
有假说认为，自然选择可降低瓶颈期内近亲繁殖种群中有害等位基因的“遗传负荷”，从而减轻未来近亲繁殖的影响。我们通过监测3058对繁殖产生的3604窝小鼠的配对成功率、窝仔数、活力和生长情况，测试了在10代实验室近亲繁殖过程中，自然选择清除鹿鼠三个亚种有害等位基因的效率。在灰腹鹿鼠中，任何一个适合度组分的近亲繁殖衰退在各代间均未降低。强烈有害的隐性等位基因可能在之前野外局部近亲繁殖过程中已被清除，该种群中残留的遗传负荷在实验室选择过程中未进一步降低。在罗德氏鹿鼠中，七个适合度组分中的四个确实显示随着近亲繁殖的持续，遗传负荷有所降低。如果该种群的近亲繁殖衰退是由高度有害的隐性等位基因引起，且这些等位基因能被选择有效清除，那么遗传负荷的平均降低幅度符合预期。对于在野外经历周期性瓶颈的白腹鹿鼠种群，实验室中进一步近亲繁殖的影响是加剧而非降低遗传负荷。隐性有害等位基因可能在野外反复出现的瓶颈期已从该种群中被清除；该种群可能已接近杂合度的阈值水平，低于此水平适合度会迅速下降。因此，选择对近亲繁殖衰退的影响在不同种群间差异很大，这可能是由于近亲繁殖和选择的历史不同所致。
