Using multispecies evolutionary history to test hypotheses of community assembly

世界上的生物多样性是由复杂的动物（尤其是昆虫）和植物群落主导的。虽然我们对这些群落是如何运作的有所了解（例如，谁吃谁），但我们对它们是如何形成的知之甚少：它们是由相互作用了数百万年的物种组成的，还是由最近才从不同来源聚集在一起的物种组成的？哪一个是正确的对于我们解释捕食者和猎物的适应方式很重要。长期的联系意味着捕食者和猎物可能已经进化出了对彼此非常特定的反应——这种进化形式通常被称为“军备竞赛”。相反，如果群落是最近才组合在一起的，组成物种的生物学不太可能是由其他群落成员塑造的。哪一种说法是正确的在物种保护中也很重要：如果物种有共同的漫长进化史，那么它们之间的相互作用（比如捕食者吃掉猎物，或者传粉者与植物的关系）也是古老的、特殊的，应该被保存下来。相反，如果群落通常是在短时间内（在进化的时间尺度上）从现有的物种集合中聚集起来的，那么它表明群落的相互作用也可以相对较快地进化，并且群落在进化上是年轻的。如果群落是年轻的，这也意味着它们很容易受到新物种的入侵——需要对人类有意或无意引入的物种进行仔细管理（如生物防治剂）。在这个项目中，我们将找出哪一种情况更适用于一个特定的群落——栖息在橡树和其他植物瘿上的昆虫。这些群落易于研究，并且在许多重要方面与其他昆虫-植物群落相匹配。我们将使用DNA序列来确定不同类型的捕食者和猎物在瘿群落的起源，然后传播到世界各地。如果群落中的物种有很长的共同历史，那么我们预计每个物种都起源于同一个地方，并以同样的方式传播。相比之下，如果捕食者在进化过程中的一系列时间点上“锁定”了猎物，那么我们预计不同的群落成员有不同的起源和范围扩张模式。我们将从两个层面来看这个问题——全球（北美、亚洲和欧洲）和区域（包括欧洲和小亚细亚在内的古北极西部）。我们项目的一个重要组成部分是评估欧洲东部地区（特别是土耳其）对欧洲保护的重要性。许多“欧洲”物种（如“英国橡树”和家鼠）在欧洲东部被发现，但东部地区的保护价值通常没有被考虑到。我们正在研究的橡树瘿蜂系统的初步信息表明，橡树和瘿蜂在传播到欧洲之前都在那里多样化。我们将观察橡树瘿中的捕食者，看看这种“来自东方”的模式是否适用于整个群落。

The world's biodiversity is dominated by complex communities of animals (particularly insects) and plants. Though we know something of how these communities function (for example, who eats whom), we know very little about how they come to be: do they consist of species that have interacted for millions of years, or do they consist instead of sets of species that have only very recently come together from different sources? Which of these is true is important for the way in which we interpret adaptations in predators and prey. Long associations mean that predators and prey may have evolved very specific responses to each other - in a form of evolution commonly termed an 'arms race'. In contrast, if communities are only recently put together, the biology of component species is unlikely to have been shaped by the other community members. Which of these is true is also likely to be important in conservation: if species share a long evolutionary history, then the interactions they share (such as a predator eating its prey, or a pollinator's relationship with a plant) are also ancient, special, and should be preserved. In contrast, if communities are commonly assembled over short periods (on an evolutionary timescale) from available sets of species, then it shows that community interactions can also evolve relatively quickly, and that communities are evolutionarily young. If communities are young, it also means that they are vulnerable to invasion by new species - requiring careful management of species that humankind introduces either intentionally (as in biocontrol agents) or unintentionally. In this project, we will work out which of these scenarios is more true for one particular community - the insects inhabiting galls on oaks and other plants. These communities are easy to study, and match in many important respects other insect-plant communities. We will use DNA sequences to work out where different types of predators and prey in the gall communities originated and then spread around the world. If species in communities have a long shared history, then we expect each species to originate in the same place and spread in the same way. In contrast, if predators have 'latched on' to their prey at a range of points through evolutionary time, then we expect different community members to have different origins and patterns of range expansion. We will look at the question at two levels - globally (across North America, Asia and Europe), and regionally (for the Western palaearctic, which includes Europe and Asia Minor). An important component of our project is assessing the importance of regions just east of Europe (particularly Turkey) for European conservation. Many 'European' species (such as the 'English oak', and house mouse) are found far to the east of Europe, but the conservation value of eastern regions is not usually considered. Initial information for the oak gallwasp system we are studying suggests that oaks and gallwasps both diversified there before spreading into Europe. We will look at the predators in oak galls to see if this 'out of the east' pattern is in fact true for the whole community.