Evolutionary rescue and the limits to phenotypic plasticity: testing theory in the field

快速的气候变化和栖息地丧失将导致许多物种在本世纪灭绝，除非它们能科普不断变化和更极端的生态条件。因此，了解是什么限制了物种的生态容忍度是一个至关重要的科学问题，因为它使我们能够预测环境变化对种群的持续影响，从而对生态群落产生影响。生物体应对环境变化的一种常见方式是“可塑性”，即直接改变其形态、生理或行为特征（表型）以应对当地环境，而不需要快速的进化变化。这种“表型可塑性”缓冲了环境的变化，并且可以在一个物种通常经历的环境范围内保持适应性。目前，全球生物多样性对气候变化的响应大多被归因于表型可塑性，而不是实际的进化变化，强调了表型可塑性在维持生态产出方面的重要性，但表型可塑性科普环境变化的能力是有限的。维持基因表达的变异不仅可能需要耗费大量的能量，而且它还只能在物种最近经历的环境范围内进化以维持适应性。因此，在新的或极端的条件下，没有理由认为一个物种的可塑性反应仍然会提高它们的生存和繁殖后代的能力。相反，在以前的环境中适应的可塑性反应实际上可能会降低他们在新环境中的适应性。这一想法尤其令人担忧，因为它预测随着生态变化的继续，可塑性将无法科普，导致人口突然下降，因为超过了关键的环境限制。相比之下，其他理论模型预测，塑料反应将能够在新的环境中更快地进化，产生比普通花园条件下实验室实验预测的更快的进化反应。我们将测试这些理论预测，通过测量两个生态不同的物种的豚草（属千里光）的海拔位置的变化，无论是内部和外部的流行分布在埃特纳山，西西里的斜坡上的塑料反应。本文报道了千里光Senecio aethnensis和千里光S.不同的表型性状，以及在表达的关键基因，与适应不同的海拔高度。我们将这两个物种的基因型移植到一系列田间条件下，并在两年的时间内监测它们的表现和可塑性，以确定每个基因型对正常（“家庭”）环境以外条件的反应。我们将测量生长和发育参数，生殖参数作为衡量每个基因型的本地健身，并测试在何种程度上的健身预期与海拔变化的下降被抵消塑性变化的表型和基因表达。我们预测，虽然观察到的塑料反应将保持个人的健康和生产力在其物种的通常范围内的海拔条件下，表型反应将不再是适当的海拔变化超过这些限制。这样一个经验发现将对预测物种对气候变化的持续可塑性反应能力具有重要意义。特别是，它将建议，快速进化将是必要的，以防止人口和物种的灭绝，环境变化的速度超过其地理范围内的普遍条件。

Rapid climate change and habitat loss will cause many species to become extinct this century unless they can cope with changing and more extreme ecological conditions. Understanding what limits species' ecological tolerances is therefore an issue of critical scientific importance because it allows us to predict the consequences of ongoing rates of environmental change to populations and therefore to ecological communities. A common way that organisms deal with environmental variation is to be 'plastic', i.e. to change their morphological, physiological or behavioural traits (their phenotypes) directly in response to their local environment, without requiring rapid evolutionary change. Such 'phenotypic plasticity' buffers changes in the environment, and can maintain fitness across the range of environments typically experienced by a species. Currently, most of the global responses of biodiversity to climate change have been ascribed to such phenotypic plasticity, rather than to actual evolutionary change, underlining its importance in maintaining ecological outputs.However, the ability of phenotypic plasticity to cope with environmental change has limits. Not only is maintaining variation in gene expression likely to be energetically expensive, it also evolves to maintain fitness only within the range of environments a species experiences in its recent past. In novel or extreme conditions, there is therefore no reason that a species' plastic responses will still improve their ability to survive and produce offspring. Instead, plastic responses that were adaptive in former environments may actually reduce their fitness in new environments. This idea is especially worrying because it predicts that plasticity will be unable to cope as ecological change continues, leading to sudden population declines as critical environmental limits are exceeded. By contrast, other theoretical models predict that plastic responses will be able to evolve more quickly in novel environments, generating faster evolutionary responses than predicted by laboratory experiments under common garden conditions. We will test these theoretical predictions by measuring the plastic responses of two ecologically divergent species of ragwort (genus Senecio) to changes in their altitudinal position, both within and outside their prevailing distributions on the slopes of Mount Etna, Sicily. These species, Senecio aethnensis and S. chrysanthemifolius differ in a number of phenotypic traits, as well as in the expression of key genes that are associated with adaptation to different altitudes. We will transplant genotypes of both species into a range of field conditions and monitor their performance and plasticity over a two-year period in order to determine each genotype's response to conditions outside its normal ('home') environment. We will measure growth and development parameters, and reproductive parameters as a measure of each genotype's local fitness, and test the degree to which the declines in fitness expected with changes in altitude are offset by plastic changes in their phenotype and in gene expression. We predict that although observed plastic responses will keep individuals healthy and productive under their species' usual range of altitudinal conditions, phenotypic responses will no longer be appropriate with altitudinal changes beyond these limits. Such an empirical finding will have important implications for predicting the continued ability of species to respond plastically to climate change. In particular, it will suggest, the rapid evolution will be necessary to prevent population and species' extinction where rates of environmental change exceed prevailing conditions within their geographical range.