Department of Biology, University of Padova, Padova, Italy.
Current Address: Department of Medicine, University of Padova, Padova, Italy.
Evolution. 2018 Mar;72(3):698-706. doi: 10.1111/evo.13425. Epub 2018 Feb 2.
Sperm competition is taxonomically widespread in animals and is usually associated with large sperm production, being the number of sperm in the competing pool the prime predictor of fertilization success. Despite the strong postcopulatory selection acting directionally on sperm production, its genetic variance is often very high. This can be explained by trade-offs between sperm production and traits associated with mate acquisition or survival, that may contribute to generate an overall stabilizing selection. To investigate this hypothesis, we first artificially selected male guppies (Poecilia reticulata) for high and low sperm production for three generations, while simultaneously removing sexual selection. Then, we interrupted artificial selection and restored sexual selection. Sperm production responded to divergent selection in one generation, and when we restored sexual selection, both high and low lines converged back to the mean sperm production of the original population within two generations, indicating that sperm number is subject to strong stabilizing total sexual selection (i.e., selection acting simultaneously on all traits associated with reproductive success). We discuss the possible mechanisms responsible for the maintenance of high genetic variability in sperm production despite strong selection acting on it.
精子竞争在动物界中广泛存在，通常与大量精子生产有关，竞争池中精子的数量是受精成功的主要预测因素。尽管强烈的后交配选择对精子生产具有定向作用，但它的遗传方差通常非常高。这可以通过精子生产与与配偶获得或生存相关的特征之间的权衡来解释，这些特征可能有助于产生整体稳定选择。为了验证这个假设，我们首先对雄性孔雀鱼（Poecilia reticulata）进行了三代的高、低精子生产的人工选择，同时去除了性选择。然后，我们中断了人工选择并恢复了性选择。精子生产在一代中对分歧选择做出了反应，当我们恢复性选择时，高、低系都在两代内回到了原始种群的平均精子生产水平，这表明精子数量受到强烈的稳定的总性选择（即同时对所有与繁殖成功相关的特征进行选择）的影响。我们讨论了维持精子生产高遗传变异性的可能机制，尽管对其进行了强烈的选择。
