Department of Biology, Section for Genetics, Ecology and Evolution, Aarhus University, Aarhus, Denmark.
Department of Biology, Lund University, Lund, Sweden.
Heredity (Edinb). 2021 Jul;127(1):10-20. doi: 10.1038/s41437-021-00436-7. Epub 2021 Apr 26.
Inbreeding depression (ID) has since long been recognized as a significant factor in evolutionary biology. It is mainly the consequence of (partially) recessive deleterious mutations maintained by mutation-selection balance in large random mating populations. When population size is reduced, recessive alleles are increasingly found in homozygous condition due to drift and inbreeding and become more prone to selection. Particularly at slow rates of drift and inbreeding, selection will be more effective in purging such alleles, thereby reducing the amount of ID. Here we test assumptions of the efficiency of purging in relation to the inbreeding rate and the experimental conditions for four traits in D. melanogaster. We investigated the magnitude of ID for lines that were inbred to a similar level, F ≈ 0.50, reached either by three generations of full-sib mating (fast inbreeding), or by 12 consecutive generations with a small population size (slow inbreeding). This was done on two different food media. We observed significant ID for egg-to-adult viability and heat shock mortality, but only for egg-to-adult viability a significant part of the expressed inbreeding depression was effectively purged under slow inbreeding. For other traits like developmental time and starvation resistance, however, adaptation to the experimental and environmental conditions during inbreeding might affect the likelihood of purging to occur or being detected. We discuss factors that can affect the efficiency of purging and why empirical evidence for purging may be ambiguous.
近亲繁殖衰退（ID）长期以来一直被认为是进化生物学中的一个重要因素。它主要是由于（部分）隐性有害突变在大随机交配群体中通过突变-选择平衡而得以维持的结果。当种群规模减小时，由于漂变和近亲繁殖，隐性等位基因越来越多地处于纯合状态，更容易受到选择的影响。特别是在漂变和近亲繁殖的缓慢速率下，选择将更有效地清除这些等位基因，从而减少 ID 的数量。在这里，我们针对四个黑腹果蝇特征，在四个实验条件下，针对近亲繁殖率，检验了清除效率的假设。我们研究了具有相似水平的近交系（F≈0.50）的 ID 幅度，这些近交系通过三代全同胞交配（快速近亲繁殖）或通过 12 代连续的小种群大小（缓慢近亲繁殖）达到。这是在两种不同的食物媒介上进行的。我们观察到卵到成虫存活率和热休克死亡率的显著 ID，但只有在缓慢近亲繁殖下，卵到成虫存活率的表达近亲繁殖衰退的很大一部分得到了有效清除。然而，对于其他特征，如发育时间和抗饥饿能力，近亲繁殖期间对实验和环境条件的适应可能会影响清除的可能性或被检测到。我们讨论了影响清除效率的因素，以及为什么清除的经验证据可能是模棱两可的。
