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

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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.