Cuckoos versus hosts: next-generation sequencing of genes for cuckoo counter-adaptations

进化过程中适应性的产生方式是目前生物学中的一个热门话题。特别是，人们对作为适应基础的遗传变化有很大的兴趣。这一点很重要，因为它使我们能够了解某些适应是否仅仅因为潜在的遗传学而比其他适应更容易出现，它可以帮助我们了解生物体如何适应环境变化。杜鹃和它们的宿主提供了一个全新的、易于处理的系统，在这个系统中可以确定自然界适应的遗传基础。研究杜鹃及其宿主的一大优势是，我们可以非常精确地衡量自然界适应性的选择优势，因为每一方都选择了直接影响生存或繁殖成功的另一方的特征。例如，田间实验表明，宿主对奇怪的蛋的排斥促使布谷鸟蛋进化成完全模仿宿主产下的蛋。卵排斥对宿主来说是适应性的，因为这意味着它们的后代不会在以后被巢中的杜鹃雏鸟杀死。对布谷鸟来说，模仿蛋是一种适应性行为，因为这意味着它们的后代在拒绝布谷鸟蛋时不会被宿主杀死。在这个项目中，我们将调查的遗传学基础的一个关键的反适应在闪亮的青铜杜鹃（Chalcides lucidus），南半球杜鹃，这表明显着的模仿小鸡着色。该物种的不同种群有不同颜色的小鸡，准确地模仿当地宿主雀形目的小鸡-因此布谷鸟小鸡在某些种群中是完全黑色的，而在其他种群中是苍白的。我们最近的实验（尚未发表）表明，通过模仿宿主幼鸟，杜鹃雏鸟不太可能被宿主识别为外来物种，因此不太可能被拒绝死亡。因此，小鸡的模仿是适应性的。此外，这是一个非常有利的遗传分析系统，因为肤色差异的遗传基础可能很简单，并且在脊椎动物中很好地理解了黑色素着色的遗传途径。在这项试验性研究中，我们建议使用下一代测序技术，根据基因表达和序列变异的差异来确定颜色变异的候选基因座。确定强候选基因座的颜色差异，这将在未来的研究中得到证实。除了颜色轨迹识别，这项工作将产生第一个大规模的基因组资源在杜鹃物种，因此将是非常有用的进化生物学家的相当大的社区工作杜鹃。我们也将能够确定潜在的候选基因座的杜鹃种群之间的羽绒差异。该项目为杜鹃与宿主的协同进化研究开辟了一条新的途径，为自然界遗传适应的研究提供了一个新的研究体系。因此，它有可能开辟一个全新的研究领域。

The way that adaptations arise during evolution is currently a hot topic in biology. In particular, there is great interest in the genetic changes that underlie adaptations. This is important because it enables us to understand whether some adaptations are more likely to arise than others simply because of the underlying genetics and it can help us understand how organisms adapt to environmental change. Cuckoos and their hosts offer a completely novel, tractable system in which to determine the genetic basis of adaptation in nature. One great advantage of working on cuckoos and their hosts is that we can measure the selective advantages of adaptations in nature very precisely because each party selects characteristics in the other that directly affect survival or reproductive success. For example, field experiments have shown that rejection of odd-looking eggs by hosts has driven the evolution of cuckoo eggs that perfectly mimic those laid by the host. Egg rejection is adaptive for hosts, because it means their offspring are not killed later by a hatchling cuckoo in the nest. Egg mimicry is adaptive for cuckoos, because it means their offspring are not killed by hosts when they reject the cuckoo egg. In this project we will investigate the genetics underlying a key counter-adaptation in the shining-bronze cuckoo (Chalcides lucidus), a southern hemisphere cuckoo which shows remarkable mimicry in chick coloration. Different populations of this species have differently coloured chicks which accurately mimic the chicks of the local host passerine - consequently cuckoo chicks are completely black in some populations, and pale in others. Our most recent experiments (still unpublished) suggest that by mimicking host young, cuckoo nestlings are less likely to be recognised as foreign by their hosts and consequently less likely to be rejected to die. Chick mimicry is therefore adaptive. Furthermore, this is a very favourable system for genetic analysis since the genetic basis of the skin colour difference is likely to be simple, and the genetic pathways underlying the black melanin coloration are well understood in vertebrates. In this pilot study we propose to use next-generation sequencing technology to identify candidate loci for colour variation based on differences in gene expression and sequence variation. The identification of strong candidate loci for the coloration difference which will be confirmed in future research. In addition to colour locus identification, the work will produce the first large scale genomic resources in a cuckoo species and will thus be of great use to the considerable community of evolutionary biologists working on cuckoos. We will also be able to identify potential candidate loci for the feather down differences between the cuckoo populations. The project represents a novel approach to the study of cuckoo-host coevolution, and offers a novel study system to the study of genetic adaptations in nature. It therefore has the potential to open up an entire new field of research.