Spatial components of plasticity in tit phenology: responses, constraints and amelioration

生物体对变化的环境有三种可能的反应方式：(1)它们可能分散或迁移，(2)它们可能进化以适应新的环境，或(3)它们可能产生不同的表型--换句话说，表现出表型可塑性--随着环境的变化。当代的一个例子涉及了解人口对气候变化的反应。迄今为止的工作表明，尽管这三种机制不是排他性的，但人口对气候变化的反应通常涉及表型可塑性。因此，理解作用于可塑性的进化力量对于我们理解面对气候变化的生存能力至关重要。表型可塑性及其在适应不断变化的环境中的作用的理解受到以下事实的阻碍：大多数研究只是将种群的平均表型与环境的单一值相关联，最常见的是在全年的水平上。只有当有机体响应的环境线索是非常大规模的线索时，这才有意义，从种群内个体的角度来看，变化很小。然而，我们知道许多生物体只经历了有限的环境部分，而且环境可能在非常小的空间范围内变化。尽管如此，我们不明白动物是如何平衡这些小规模和大规模的暗示的。因此，这项研究的中心目的是确定环境的空间尺度对理解表型可塑性进化的重要性。我们的模型系统涉及小型林地鸟类--大山雀，在牛津附近的威瑟姆森林繁殖--的繁殖行为，这些鸟类处于强烈的自然选择之下，其繁殖时间与飞蛾毛虫(如冬季飞蛾)的繁衍高峰期重合，这些毛虫适应于以新出现的落叶树叶子为食。在种群水平上，鸟类繁殖的时间与毛虫数量的高峰之间存在很好的匹配，但在相当小的空间范围内，这些事件的时间在每年都有巨大的差异。此外，我们有证据表明，尽管有共同的气温趋势，但人口的不同部分以不同的速度做出反应。因此，种群水平的汇总统计数据掩盖了几个重要的变化水平。我们将使用繁殖行为和适合度的长期数据，以及详细的环境数据来分析最能解释鸟类繁殖时间变化的空间尺度，并检验关于尺度对适合度和种群动态的影响的假设。然后，我们将用从固定地点网格收集的新数据来补充这些数据，以确定萌芽和毛虫丰度的物候，从而表征鸟类能够在多大程度上与其环境中不同规模的事件的时间相匹配。因为我们预计多个尺度是重要的，我们可以预测，最优的表型是小规模和大尺度可塑性之间的平衡，因此，孤立地在任何一个尺度上适应都不是完美的。由于环境是斑块状的，我们可以进一步预测，调整到小尺度和大尺度线索将导致某些斑块具有比其他斑块更高的生产力；因此，可塑性的空间尺度将导致种群动态的种群内变异。收集地面环境数据非常耗时，而且只能覆盖有限的区域；因此，我们将测试卫星图像在多大程度上可以用来估计与自然界中生物相关的尺度的物候。最后，我们将进行实验测试，以确定鸟类与环境之间在物候方面的不匹配是否会因处于更多样化的环境中而得到缓解。鸟类与环境之间的不匹配与某些物种的数量下降有关。

There are three potential ways in which organisms can respond to changing environments: (1) they may disperse, or migrate, (2) they may evolve so that they adapt to the new environment, or (3) they may produce different phenotypes - in other words display phenotypic plasticity - as the environment changes. A contemporary example relates to understanding responses of populations to climate change. Work to date suggests that, despite the three mechanisms being non-exclusive, population responses to climate change usually involve phenotypic plasticity. Hence, understanding the evolutionary forces acting on plasticity is of central importance in our understanding of viability in the face of climate change. Understanding of phenotypic plasticity and its role in adaptation to changing environments is hampered by the fact that most studies simply correlate an average phenotype for the population with a single value for the environment, most often at the level of an entire year. This only makes sense if the environmental cues to which organisms respond are very large-scale cues, varying little from the perspective of individuals within populations. However, we know that many organisms experience only a limited part of the environment, and that the environment may vary over quite small spatial scales. Despite this, we don't understand how animals balance these small- and large-scale cues. The central aim of this research is thus to determine how the spatial scale of the environment is important in understanding the evolution of phenotypic plasticity.Our model system involves reproductive behaviour in small woodland birds - great tits, breeding in Wytham Woods near Oxford - which are under strong natural selection to time their reproduction to coincide with peaks in abundance of moth caterpillars (e.g. the winter moth) that are adapted to feed on newly emerged leaves of deciduous trees. At the population level there is a good match between the timing of birds' breeding and the peak of caterpillar abundance, but there is tremendous variation within each year in the timing of these events over quite a small spatial scale. Furthermore, we have evidence that, despite a common temperature trend, different parts of the population are responding at different rates. Hence, the population level summary statistics disguise several important levels of variation.We will use long term data on breeding behaviour and fitness, together with detailed environmental data to analyse the spatial scales at which variation in bird reproductive timing can best be explained, and to test hypotheses about the influence of scale on fitness and population dynamics. We will then supplement these data with new data collected across a regular grid of locations to determine phenology of bud-burst and caterpillar abundance, and hence characterise the extent to which birds are able to match the timing of events in their environment at different scales. Because we expect multiple scales to be important, we can make the prediction that the optimal phenotype is a balance between small- and large-scale plasticity, and hence that adaptation will not be perfect at either scale in isolation. Because the environment is patchy, we can further predict that adjusting to small- as well as large-scale cues will lead to some patches having higher productivity than others; hence the spatial scale of plasticity will lead to within population variation in population dynamics. Collecting environmental data on the ground is very time-consuming, and only limited areas can be covered; therefore we will test the extent to which satellite images can be used to estimate phenology at scales that are relevant to organisms in nature. Finally, we will carry out experimental tests of whether mis-matches in phenology between birds and the environment, which have been implicated in population declines in some species, are alleviated by being in more varied environments.