Environmental dependence of inbreeding depression and purging in Drosophila melanogaster
Environmental dependence of inbreeding depression and purging in Drosophila melanogaster
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DOI：
10.1046/j.1420-9101.1999.00113.x
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发表时间：
1999-11-01
影响因子：
2.1
通讯作者：
Van Putten, WF
中科院分区：
文献类型：
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作者：
Bijlsma, R;Bundgaard, J;Van Putten, WF
消除或减少近交衰退的自然选择在贡献位点（清洗）已被假设，以有效地减轻近亲繁殖的负面影响，在小孤立的群体。然而，这可能仅在环境条件相对恒定时才有效。我们用果蝇作为模式生物来检验这一假设。通过染色体平衡仪，从野生种群中取样染色体，并在有利的环境中在纯合和杂合条件下估计它们的生活力。大约50%的染色体被发现携带致命或亚致命突变，这在近亲繁殖时会导致相当数量的近亲繁殖衰退。通过仅选择在纯合条件下具有与杂合子（准正常）相当的活力的染色体，人工清除这些隐性等位基因，从而去除大多数有害的隐性等位基因。接下来，在不同的环境胁迫条件下（高温胁迫、DDT胁迫、乙醇胁迫和拥挤），对这些准正常个体的卵至成虫的生存能力和总适合度进行了测试。在这些改变的压力条件下，特别是高温和DDT，新的隐性有害影响的表达是不明显的控制条件下。其中一些染色体甚至被发现在压力下携带致命或接近致命的突变。与杂合子相比，纯合子表现出平均25%的额外减少总适合度。我们的结果表明，除了在所有环境条件下影响适应度的突变之外，近交衰退可能是由于不同环境中的不同基因座造成的。因此，有害隐性等位基因的清除仅对清除发生的特定环境有效，因为在变化的环境条件下会表达额外的负荷。这些结果不仅表明，近交衰退是环境依赖性的，而且近交衰退可能会变得更加严重，在不断变化的压力条件。这些观察结果对保护生物学有重要影响。
Elimination or reduction of inbreeding depression by natural selection at the contributing loci (purging) has been hypothesized to effectively mitigate the negative effects of inbreeding in small isolated populations. This may, however, only be valid when the environmental conditions are relatively constant. We tested this assumption using Drosophila melanogaster as a model organism. By means of chromosome balancers, chromosomes were sampled from a wild population and their viability was estimated in both homozygous and heterozygous conditions in a favourable environment. Around 50% of the chromosomes were found to carry a lethal or sublethal mutation, which upon inbreeding would cause a considerable amount of inbreeding depression. These detrimentals were artificially purged by selecting only chromosomes that in homozygous condition had a viability comparable to that of the heterozygotes (quasi-normals), thereby removing most deleterious recessive alleles. Next, these quasi-normals were tested both for egg-to-adult viability and for total fitness under different environmental stress conditions: high-temperature stress, DDT stress, ethanol stress, and crowding. Under these altered stressful conditions, particularly for high temperature and DDT, novel recessive deleterious effects were expressed that were not apparent under control conditions. Some of these chromosomes were even found to carry lethal or near-lethal mutations under stress. Compared with heterozygotes, homozygotes showed on average 25% additional reduction in total fitness. Our results show that, except for mutations that affect fitness under all environmental conditions, inbreeding depression may be due to different loci in different environments. Hence purging of deleterious recessive alleles can be effective only for the particular environment in which the purging occurred, because additional load will become expressed under changing environmental conditions. These results not only indicate that inbreeding depression is environment dependent, but also that inbreeding depression may become more severe under changing stressful conditions. These observations have significant consequences for conservation biology.