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，每一个这些前提是一个强大的和可靠的系统发育假说，以提供方向和时间的进化事件，并揭示驱动进化分歧的潜在过程（模式）。当小心实施时，遗传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，这就是为什么它们已经成为研究各种生物进化机制的重要工具。尽管它们的世界性，丰富，进化意义和医疗用途，没有系统发育假说存在的水蛭（水蛭），这使得推论有关该组的进化不必要的费力。除了为水蛭的进化提供一个总体框架外，水蛭发生是解决水蛭进化中两个突出问题的重要组成部分。(i)什么是基因组组成，即，什么基因被表达，有没有丢失，有没有在不同的分类群中被重新排列（目前只有一个基因组存在，这掩盖了在远亲分类群之间进行比较分析的可能性）。此外，（ii）通过破译经常用于中风患者愈合以及皮瓣和手指再植手术后的抗凝因子的多样性、选择和进化历史，可以获得关于这些医学上重要的动物中吸血进化的知识，以及细菌共生体的功能和系统发育史，这些共生体似乎在水蛭的生长和喂养策略中起着至关重要的作用。我的研究计划将使用大规模测序工作来阐明这些问题，并推断出一个坚实的子类范围内的同源性，通过测序一个完整的水蛭基因组（目标1），目标捕获序列约100终端（目标2），唾液转录组的10个物种（目标3）和完整的细菌基因组的5个细胞内细菌共生体（目标4）。为此，将在三大洲（北美[主要是加拿大]、南美和亚洲）进行实地考察，并将尖端测序技术与复杂的下游生物信息学相结合。总之，这些项目将为水蛭吸血的进化提供一个新的现代视角。

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.