The capacity for sustained adaptation in a rapidly changing environment

澳大利亚的珊瑚正在遭受痛苦，它们是海洋变暖导致的“珊瑚白化”的受害者。当这些色彩斑斓的水下动物驱逐它们的藻类伙伴，从而变成白色时，它们可能向我们传递了两个信息，这些信息可能会在未来几年定义地球的生物群。其一，地球正在以数百万年来最快的速度变暖，联合国气候科学家的最新报告警告说，与这种变暖有关的一些环境变化可能会自我维持，扩大其自身的影响。现在人们普遍认为，全球变暖是由二氧化碳等温室气体的人为增加引起的，但无论原因是什么，地球现在比过去12.5万年都要暖和。这种新的气候，以及它带来的许多环境变化，意味着植物和动物将不得不适应生存，而这可能需要数百年到数千年的时间。在这种情况下，如果珊瑚白化持续下去，珊瑚最终会死亡。来自珊瑚的另一个信息是，我们目前对物种适应速度的看法可能是危险的乐观。对物种在野外或实验室中适应环境的研究经常表明，物种可以迅速变化。他们可以，但这些研究通常只进行了几代人，因此无法回答这样的高变化率能持续多久的问题。任何给定物种的种群在身高或体重（或对珊瑚白化的抵抗力）等特征上自然地有所不同，而自然选择正是依据这种变化而起作用，通过偏爱某些变体而不是其他变体来引起变化。但随着这个过程的进行，自然的变异会被耗尽，在这个时候，适应变得缓慢，甚至可能停止，物种可能会灭绝。根据联合国的《可持续发展报告》，“大自然正在以人类历史上前所未有的速度在全球范围内衰退——物种灭绝的速度正在加快”。这些小珊瑚可能是这种效应的首批先兆之一。物种能维持多久，以怎样的速度持续适应？我们希望进行的研究将利用地球进化史而不是短期研究得出的估计来解决这个问题。我们的方法将应用新的统计建模技术对数千个物种进行分析，以估计它们在数百万年的进化过程中过去的变化率。从这个前所未有的数据库中，我们将能够开发出可以在千年时间尺度上持续变化的数量和上限的概况。然后，利用种群内自然变化的信息，我们将能够确定这些历史变化率是否处于进化的最高水平，如果不是，估计它们可以增加多少。我们的工作将把这些方法和想法应用于所有脊椎动物（有脊椎的动物）的物种，包括哺乳动物、鸟类、鱼类、爬行动物和两栖动物。我们将能够确定哪些物种能够进行最大的适应性变化，以及像飞行或水生生物这样的特征是否与较大或较小的变化有关。我们的方法很容易应用于其他物种，并强调了预测地球生物群如何应对快速变化的世界所需要的那种信息。

Australia's corals are suffering, victims of 'coral bleaching' brought on by a warming ocean. When these colourful underwater animals expel their algal partners, thereby turning white, they may be sending us two messages that could define the Earth's biota in the coming years. One is that the Earth is now warming at rates faster than it has for millions of years, and the most recent report from the United Nation's climate scientists warns that some environmental changes in response to this warming could become self-sustaining, amplifying their own effects. There is now wide agreement that global warming has been brought on by anthropogenic (human-induced) increases in greenhouse gases such as carbon dioxide, but whatever the causes, the Earth is now warmer than it has been for 125,000 years. This new climate, and the many environmental changes it brings, mean that the plants and animals are going to have to adapt to survive, and do so over timescales of potentially many hundreds to thousands of years. In this context, if coral bleaching persists, the corals eventually die.The other message from the corals is that our current views on how rapidly species can adapt might be dangerously optimistic. Studies of species adapting in the wild, or in laboratory experiments, often reveal that species can change rapidly. They can, but these studies typically take place over a handful of generations and thereby fail to answer the question of for how long such high rates of change can be sustained. Populations of any given species naturally vary in features such as height or weight (or resistance to coral bleaching), and it is this variation that natural selection acts upon, causing change by favouring some variants over others. But as this process goes on, the natural variation gets used up, and at that point adaptation slows to a crawl, or can even stop, and species can go extinct. Already, according to the United Nations' Sustainable Development report "Nature is declining globally at rates unprecedented in human history - and the rate of species extinctions is accelerating". The tiny corals might be among the first harbingers of this effect.For how long and at what rates can species maintain sustained bouts of adaptation? The research we wish to conduct will address this question using estimates derived not from short-term studies but from the Earth's evolutionary history. Our approach will apply new statistical modelling techniques to thousands of species to estimate their past rates of change over millions of years of evolution. From this unprecedented database we will be able to develop profiles of the amounts and upper limits of change that can be sustained over millennial timescales. Then, using information on the natural variation within populations, we will be able to determine if these historical rates of change are at their evolutionary maximums, and if not, estimate how much they could be increased. Our work will apply these methods and ideas to species from all of the Classes of vertebrates (animals with a backbone), including mammals, birds, fish, reptiles and amphibians. We will be able to identify which kinds of species are capable of the greatest adaptive change, and whether traits like flying or an aquatic existence are associated with greater or lesser amounts of change. Our approach is easily applied to other species, and highlights the kind of information that will be needed to make predictions about how the Earth's biota might change in response to a rapidly changing world.