Bonnet Timothée, Wandeler Peter, Camenisch Glauco, Postma Erik
Department of Evolutionary Biology and Environmental Studies, University of Zurich, Zurich, Switzerland.
Natural History Museum Fribourg, Fribourg, Switzerland.
PLoS Biol. 2017 Jan 26;15(1):e1002592. doi: 10.1371/journal.pbio.1002592. eCollection 2017 Jan.
In natural populations, quantitative trait dynamics often do not appear to follow evolutionary predictions. Despite abundant examples of natural selection acting on heritable traits, conclusive evidence for contemporary adaptive evolution remains rare for wild vertebrate populations, and phenotypic stasis seems to be the norm. This so-called "stasis paradox" highlights our inability to predict evolutionary change, which is especially concerning within the context of rapid anthropogenic environmental change. While the causes underlying the stasis paradox are hotly debated, comprehensive attempts aiming at a resolution are lacking. Here, we apply a quantitative genetic framework to individual-based long-term data for a wild rodent population and show that despite a positive association between body mass and fitness, there has been a genetic change towards lower body mass. The latter represents an adaptive response to viability selection favouring juveniles growing up to become relatively small adults, i.e., with a low potential adult mass, which presumably complete their development earlier. This selection is particularly strong towards the end of the snow-free season, and it has intensified in recent years, coinciding which a change in snowfall patterns. Importantly, neither the negative evolutionary change, nor the selective pressures that drive it, are apparent on the phenotypic level, where they are masked by phenotypic plasticity and a non causal (i.e., non genetic) positive association between body mass and fitness, respectively. Estimating selection at the genetic level enabled us to uncover adaptive evolution in action and to identify the corresponding phenotypic selective pressure. We thereby demonstrate that natural populations can show a rapid and adaptive evolutionary response to a novel selective pressure, and that explicitly (quantitative) genetic models are able to provide us with an understanding of the causes and consequences of selection that is superior to purely phenotypic estimates of selection and evolutionary change.
在自然种群中，数量性状动态往往似乎并不遵循进化预测。尽管有大量自然选择作用于可遗传性状的例子，但野生脊椎动物种群当代适应性进化的确凿证据仍然很少，而且表型停滞似乎是常态。这种所谓的“停滞悖论”凸显了我们预测进化变化的无能，这在快速的人为环境变化背景下尤其令人担忧。虽然导致停滞悖论的原因备受争议，但缺乏旨在解决这一问题的全面尝试。在这里，我们将定量遗传框架应用于一个野生啮齿动物种群基于个体的长期数据，结果表明，尽管体重与适合度之间存在正相关，但体重却出现了向更低值的遗传变化。后者代表了对生存选择的一种适应性反应，这种选择有利于成长为相对较小成年个体（即成年后潜在体重较低）的幼年个体，这些个体可能更早完成发育。这种选择在无雪季节末期尤为强烈，并且近年来有所加剧，这与降雪模式的变化相吻合。重要的是，无论是负面的进化变化，还是驱动它的选择压力，在表型层面都不明显，它们分别被表型可塑性以及体重与适合度之间的非因果（即非遗传）正相关所掩盖。在遗传层面估计选择使我们能够揭示正在发生的适应性进化，并识别相应的表型选择压力。我们由此证明自然种群能够对新的选择压力表现出快速的适应性进化反应，并且明确的（定量）遗传模型能够让我们更好地理解选择作用的原因和后果，这优于单纯基于表型的选择和进化变化估计。
