Centre d'Ecologie Fonctionnelle et Evolutive (CEFE), UMR 5175, CNRS - Université de Montpellier - Université Paul Valéry Montpellier - EPHE, 1919 Route de Mende, 34293 Montpellier Cedex 5, France.
Centre d'Ecologie Fonctionnelle et Evolutive (CEFE), UMR 5175, CNRS - Université de Montpellier - Université Paul Valéry Montpellier - EPHE, 1919 Route de Mende, 34293 Montpellier Cedex 5, France.
Curr Biol. 2017 Jan 23;27(2):237-242. doi: 10.1016/j.cub.2016.11.015. Epub 2016 Dec 29.
Self-fertilization is widely believed to be an "evolutionary dead end" [1, 2], increasing the risk of extinction [3] and the accumulation of deleterious mutations in genomes [4]. Strikingly, while the failure to adapt has always been central to the dead-end hypothesis [1, 2], there are no quantitative genetic selection experiments comparing the response to positive selection in selfing versus outcrossing populations. Here we studied the response to selection on a morphological trait in laboratory populations of a hermaphroditic, self-fertile snail under either selfing or outcrossing. We applied both treatments to two types of populations: some having undergone frequent selfing and purged a substantial fraction of their mutation load in their recent history [5], and others continuously maintained under outcrossing. Populations with a history of outcrossing respond faster to selection than those that have experienced selfing. In addition, when self-fertilization occurs during selection, the response is initially fast but then rapidly slows, while outcrossing populations maintain their response throughout the experiment. This occurs irrespective of past selfing history, suggesting that high levels of inbreeding depression, contrary to expectation [6], do not set strong limits to the response to selection under inbreeding, at least at the timescale of a few generations. More surprisingly, phenotypic variance is consistently higher under selfing, although it quickly becomes less responsive to selection. This implies an increase in non-heritable variance, hence a breakdown of developmental canalization [7] under selfing. Our findings provide the first empirical support of the short-term positive and long-term negative effects of selfing on adaptive potential.
自交被广泛认为是一种“进化死胡同”[1,2]，增加了灭绝的风险[3]和基因组中有害突变的积累[4]。引人注目的是，尽管适应失败一直是死胡同假说的核心[1,2]，但没有定量遗传选择实验比较自交和异交种群对正选择的反应。在这里，我们在实验室环境下研究了一种雌雄同体、可自交的蜗牛的形态特征对选择的反应，该蜗牛在自交或异交条件下进行实验。我们对两种类型的种群应用了两种处理方法：一些种群经历了频繁的自交，并在其最近的历史中清除了大量的突变负荷[5]，而另一些种群则持续保持异交。有杂交史的种群对选择的反应比经历过自交的种群更快。此外，当自交发生在选择过程中时，反应最初很快，但随后迅速减缓，而异交种群在整个实验过程中保持其反应。这与过去的自交历史无关，表明高水平的近交衰退[6]并没有对自交条件下的选择反应设置很强的限制，至少在几代的时间尺度上是这样。更令人惊讶的是，尽管自交种群的表型方差对选择的反应很快变得不那么敏感，但它的方差始终更高。这意味着非遗传性方差增加，因此在自交条件下发育的管道化[7]崩溃。我们的发现为自交对适应潜力的短期积极和长期负面影响提供了第一个经验支持。
