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.

长期以来，近亲繁殖衰退 (ID) 一直被认为是进化生物学中的一个重要因素。这主要是大型随机交配种群中突变选择平衡维持的（部分）隐性有害突变的结果。当种群规模减少时，由于漂移和近亲繁殖，隐性等位基因越来越多地处于纯合状态，并且更容易被选择。特别是在漂移和近亲繁殖速度较慢的情况下，选择将更有效地清除此类等位基因，从而减少 ID 的数量。在这里，我们测试了与近亲繁殖率和黑腹果蝇四个性状的实验条件相关的清除效率假设。我们调查了近交到相似水平F的品系的 ID 大小 ≈ 0.50，通过三代全同胞交配（快速近亲繁殖）或连续 12 代人口规模较小（慢速近亲繁殖）达到。这是在两种不同的食物培养基上完成的。我们观察到卵对成体存活率和热休克死亡率的显着 ID，但仅对于卵对成体存活率，表达的近亲繁殖抑制的重要部分在缓慢近亲繁殖下被有效清除。然而，对于发育时间和耐饥饿性等其他性状，近亲繁殖期间对实验和环境条件的适应可能会影响清除发生或被检测到的可能性。我们讨论了可能影响清洗效率的因素，以及为什么清洗的经验证据可能不明确。