Species interactions and the evolution of biological diversity: visual signalling in antagonistic and mutalistic coevolution

世界上的许多生物多样性诞生于不同物种之间的相互作用，并且至关重要地依赖于这些相互作用。他们给我们提供了一些自然界中最令人惊讶的适应例子：杜鹃卵完美地模仿了寄主的蛋，或者长舌苍蝇为长刺兰花授粉。这些都是共同进化的产物，共同进化是两个或更多物种相互影响彼此进化的过程。但共同进化不仅是产生生物多样性的一股强大力量：它对人类面临的挑战至关重要，例如生态系统及其为我们提供的服务的保护、生物控制以及不断变化的传染病和耐药性威胁。为了应对这些挑战，我们需要彻底了解其中涉及的进化机制。这个项目旨在通过研究鸟类与它们对抗的敌手(它们的幼虫)和它们合作的互助者(它们授粉的植物)之间的相互作用，更好地了解共同进化和产生生物多样性的过程。物种之间的相互作用在热带地区最古老，在那里它们可能是最能揭示一般进化过程的地方。因此，我的寄生研究将利用在赞比亚研究的三个独立进化的热带幼虫寄生系统。像杜鹃这样的孵化寄生虫是鸟界的骗子，它们利用其他物种的照顾来抚养自己的后代。随着寄生虫进化出对宿主更好的操纵(例如对宿主卵的模仿)，宿主以越来越精细的防御(如拒绝模仿卵)做出反应，它们可能会与宿主陷入共同进化的军备竞赛。在这个项目中，我将首先询问物种之间的互动如何在个体之间产生多样性，以及这是如何由视觉感知塑造的。赞比亚的杜鹃雀和非洲杜鹃参与了鸟蛋的生物军备竞赛，不同的寄主雌性不断进化出新的卵型，以通过追逐寄生虫来逃避模仿。我会问寄主如何使它们的卵子最难被模仿(就像钞票上的水印阻止伪造者一样)，不同的寄主可能如何影响彼此的多样化，以及当寄生虫实现近乎完美的卵子伪造时，进化将如何进行。为了做到这一点，我将在寄主的巢中进行实地实验，以及计算机视觉模型，以便通过鸟眼表达鸡蛋的外观，因为鸟类的视觉比我们自己的更好。然后，我会问，类似的过程是否可能在互利互动中发挥作用：我将测试鸟类传粉者的视觉辨别是否有利于彼此附近开花的物种之间的花色差异或趋同，从而导致同一物种的植物在不同的当地社区之间多样化。第二，我将试图解决宿主-寄生虫研究的一个数百年来的难题：尽管其他宿主饲养的雄性幼虫与同一物种的不同雌性寄生虫杂交，但同一物种的不同雌性寄生虫如何产卵，模仿它们选择的宿主的卵？一种假设是，这些特殊的适应只在雌性品系中遗传，通过雌性特有的鸟类W染色体。在赞比亚，我们发现寄生雌性的血统数百万年来一直对它们选择的宿主保持着完美的忠诚，这可能使这种专门化得以进化。我建议通过定位参与不同寄主物种和不同寄主签名模仿的基因来测试这一点。我将通过对圈养的杜鹃雀进行繁殖实验，结合先进的DNA测序和对卵子形成的输卵管中基因表达的研究来做到这一点。最后，我将定位参与生成复杂卵子签名的宿主基因，以揭示类似的遗传机制是否在宿主和它们的寄生虫中一致进化，从而如此美丽地模仿它们。

Much of the world's biological diversity was born of and crucially depends upon interactions between different species. They give us some of the most astonishing examples of adaptation seen in nature: a cuckoo egg perfectly mimicking that of its host, or a long-tongued fly pollinating a long-spurred orchid. These are products of coevolution, which is the process by which two or more species reciprocally influence one another's evolution. But coevolution is not only a potent force in generating biodiversity: it is crucial to human challenges such as conservation of ecosystems and the services they provide us, biocontrol, and the ever-changing threat of infectious disease and drug resistance. To address these challenges, we need a thorough understanding of the evolutionary mechanisms involved.This project aims better to understand coevolution and the processes generating biological diversity by studying the interactions between birds and the antagonists they battle against (their brood parasites), and the mutualists they cooperate with (the plants they pollinate). Interactions between species are at their most ancient in the tropics, where they might be most revealing of general evolutionary processes. My parasitic research will therefore exploit three independently evolved tropical brood parasitic systems studied in Zambia. Brood parasites such as cuckoos are the cheats of the bird world, that exploit the care of other species to raise their young. They can become locked in coevolutionary arms races with their hosts, as parasites evolve ever better manipulation of hosts (such as mimicry of host eggs), and hosts respond with ever more refined defences (such as rejecting mimetic eggs).In this project, I will first ask how interactions between species can generate diversity among individuals, and how this is shaped by visual perception. The Cuckoo Finch and African Cuckoo in Zambia are involved in biological arms races in bird egg appearance, whereby different host females are continually evolving new egg types to escape mimicry by their pursuing parasite. I will ask how hosts might make their eggs most difficult to mimic (just as the watermarks of banknotes deter forgers), how different hosts might affect one another's diversification, and how evolution proceeds when parasites achieve almost perfect egg forgeries. To do so I will carry out field experiments at hosts nests, together with computer modelling of vision in order to express egg appearance through a bird's eye, since birds vision is superior to our own. I will then ask whether similar processes might operate in mutualistic interactions: I will test whether visual discrimination by bird pollinators favours flower colour divergence or convergence between species flowering near one another, and thus cause plants of the same species to diversify between different local communities.Second, I will attempt to solve a centuries-old conundrum for host-parasite research: how do different female brood parasites of the same species lay eggs that mimic those of their chosen host, despite interbreeding with males raised by other hosts? An hypothesis is that these specialised adaptations are inherited in the female line alone, via the female-specific avian W chromosome. In Zambia we have discovered that lineages of parasitic females have stayed perfectly faithful to their chosen hosts for millions of years, which could allow such specialisation to evolve. I propose to test this by locating the genes involved in mimicry of different host species and different host signatures. I will do so by way of breeding experiments on captive Cuckoo Finches, in combination with advanced DNA sequencing and studies of gene expression in the oviduct where eggs are formed. Finally, I will locate the host genes involved in generating complex egg signatures, to reveal whether similar genetic mechanisms have convergently evolved both in hosts and their parasites that so beautifully mimic them.