Inbreeding depression is a key factor in the evolution of mating strategies and breeding systems across the eukaryotic tree of life. Yet its potential impact in partially asexual species has only received little attention. We studied inbreeding depression in the cyclical parthenogen Daphnia magna by following mixtures of inbred and outbred genotypes from an early embryonic stage through hatching to adulthood and then across several asexual generations. We found that, across asexual generations, the frequency of inbred genotypes strongly and constantly decreased, until the experimental populations were almost entirely made up of outbred genotypes. The resulting estimate of inbreeding depression across the entire life cycle was almost 100 %, much higher than previous estimates for this and other similar species. Our results illustrate that the magnitude of inbreeding depression may be severely underestimated in studies that use fitness components or proxies instead of compound fitness estimates across the entire life, as well as in experimental studies with substantial pre-experimental mortality. More generally, our results suggest that inbreeding depression may play an important role in the evolution of partially asexual life cycles because clonal reproduction maintains inbreeding levels, and hence the negative effects of inbreeding accumulate across subsequent asexual generations.

中文翻译：

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部分性无性恋加剧了大型蚤的强烈的整个生命周期近交抑郁

近亲繁殖抑郁是整个真核生物树上交配策略和繁殖系统进化的关键因素。然而，它对部分无性物种的潜在影响只受到很少的关注。我们通过追踪近交和近交基因型的混合物，研究了从早期胚胎阶段到孵化到成年期，然后跨越多个无性世代的周期性孤雌生殖Daphnia magna的近交衰退。我们发现，在无性世代中，近交基因型的频率强烈且不断下降，直到实验种群几乎完全由远交基因型组成。在整个生命周期中对近亲衰退的估计结果几乎为100％，远高于此前对该物种和其他类似物种的估计。我们的结果表明，在整个生命周期中使用适应度分量或代理代替复合适应度估计的研究中，以及在实验前死亡率很高的实验研究中，近亲抑郁的严重程度可能会被严重低估。更普遍地说，我们的研究结果表明近交抑郁在部分无性生活周期的演变中可能起重要作用，因为克隆繁殖维持近交水平，因此近亲繁殖的负面影响会在随后的无性世代中积累。