Unraveling the evolutionary history of leeches: phylogenomics and the evolution of bloodfeeding

了解行为、生态和形态的进化转变，以及生物多样性的起源和分布，是生物学的基础。然而，其中每一个都以一个强大而可靠的系统发育假说为前提，以给出进化事件的方向和时间，并揭示驱动进化分歧的潜在过程(模式)。当小心实施时，系统发育学为一个群体的系统学提供了科学基础，并可能为过去的进化事件提供信息，这就是为什么它们成为研究广泛生物进化机制的重要工具。尽管它们具有世界性、丰富性、进化意义和医学用途，但对于水蚤亚纲来说，并不存在系统发育假说，这使得关于该群体的进化的推断变得不必要地费力。除了为水蚤的进化提供一个一般框架外，系统发育也是解决两个突出问题的重要组成部分，这两个问题是关于水蚤进化的突出问题。(I)基因组的组成是什么，即表达了什么基因，有哪些基因已经丢失或在不同的分类群之间重新排列(目前只有一个基因组，这掩盖了在遥远的亲缘分类群之间进行比较分析的可能性)。此外，(Ii)通过破译在中风患者的愈合和断指再植手术后经常使用的抗凝血因子的多样性、选择和进化史，以及似乎在水蚤的生长和进食策略中发挥关键作用的细菌共生体的功能和系统发育史，可以获得关于这些具有重要医学意义的动物的血液喂养进化的知识。我的研究计划将使用大规模测序工作来阐明这些问题，并通过测序水蚤的完整基因组(目标1)、~100个末端的靶标捕获序列(目标2)、10个物种的唾液转录本(目标3)和5个细胞内细菌共生体的完整细菌基因组(目标4)，来揭示这些问题并推断出坚实的亚纲范围的系统发育。为此，将在三大洲(北美[主要是加拿大]、南美和亚洲)进行实地工作，尖端测序技术将与复杂的下游生物信息学相结合。综上所述，这些项目将提供一种全新的、现代的视角来看待水蚤的进食进化。

Understanding evolutionary transitions in behaviour, ecology and morphology, as well as the origin and distribution of biological diversity, is fundamental in biology. However, each of these presupposes a robust and reliable phylogenetic hypothesis to give direction and timing to evolutionary events and to reveal the underlying processes (mode) driving evolutionary divergence. When implemented with care, phylogenies provide the scientific basis for the systematics of a group and may inform on past evolutionary events, which is why they have become vital tools for studying the mechanisms of evolution for a wide array of organisms. Despite of their cosmopolitan nature, abundance, evolutionary significance and medical utility, no phylogenetic hypothesis exists for the subclass Hirudinea (leeches), which makes inferences regarding the evolution of the group unnecessarily strenuous. Beyond providing a general framework for the evolution across leeches, the phylogeny is an important component in addressing two outstanding questions that are conspicuous regarding the evolution of leeches. (i) What is the genomic makeup, i.e., what genes are expressed, have any been lost and have any been rearranged across different taxa (only a single genome currently exists, which belies the possibility of comparative analyses between distantly related taxa). Further, (ii) what knowledge can be gained regarding the evolution of bloodfeeding in these medically important animals by deciphering both the diversity, selection and evolutionary histories of the anticoagulation factors that are frequently used in the healing of stroke patients and following flap and digit replantation surgery, as well as the function and phylogenetic histories of the bacterial symbionts that seem to play a vital role in leech growth and feeding strategies. My research programme will use large-scale sequencing efforts to shed light on these questions and to infer a solid subclass-wide phylogeny, by sequencing a full leech genome (Objective 1), target-capture sequences for ~100 terminals (Objective 2), salivary transcriptomes for 10 species (Objective 3) and full bacterial genomes for five intracellular bacterial symbionts (Objective 4). To this end, fieldwork will be conducted on three continents (North America [mainly Canada], South America and Asia), and cutting-edge sequencing technologies will be coupled with sophisticated downstream bioinformatics. Taken together, these projects will provide a fresh and modern view of the evolution of bloodfeeding in leeches.