Hemichordates are a group of marine invertebrates comprising over 100 species of solitary and colonial wormlike creatures. Hemichordates have figured prominently in hypotheses of the evolutionary origins of chordates because they are relatively primitive relatives of vertebrate animals. Because of their primitiveness, hemichordates also provide a key comparison group to understand the evolution of key innovations of vertebrates, such as gill slits and a hollow nerve chord. However, hemichordates have not been studied in depth, and evolutionary relationships within the group are not well understood. The proposed work will use genomic approaches to identify genes that will elucidate evolutionary relationships among the hemichordates and clarify the evolutionary history of the vertebrates in a broader sense. Results of this research will provide a greater understanding of cellular, genetic, and developmental programs that were likely present in the ancestral lineage that led to chordates and have been evolutionarily conserved during vertebrate evolutionary history.
Understanding hemichordate evolution is central to research in fields ranging from neurobiology to developmental biology to physiology, and the results of this research will be of wide interest to many fields of science. The project will support training of students at various levels from K-12 to graduate school. Undergraduates, including members of underrepresented groups, will participate in the project through courses on the campuses of Auburn University, the University of Washington, and the Friday Harbor marine laboratories. The research will be publicized through talks to public schools, web-based outlets, and introductory biology textbooks.
Scientific Merit Hemichordates have long been pivotal to hypotheses of deuterostome evolution and chordate origins. EST-based phylogenetic studies to date lack sufficient representations of hemichordates, which have both solitary (enteropneust worm) and colonial (pterobranch) forms with strikingly different morphologies. Pterobranchia, which was absent from these studies and is the last remaining deuterostome body plan lacking genomic characterization, has been central to hypotheses of the last common deuterostome ancestor for over 60 years. Furthermore, evolutionary relationships within hemichordates are a complete mystery, yet understanding of hemichordate phylogeny is needed to assess ancestral character states of Ambulacraria (echinoderms & hemichordates) and deuterostomes. In this project we undertook traditional gene-based approaches as well as a more holistic genomic approach to critically reevaulate recent hypotheses of deuterostome evolution by focusing on the history and placement of hemichordate lineages. Phylogenetic hypotheses resulting from this work will have profound implications for our understanding of when, and in which taxa, characters traditionally ascribed to chordates arose (e.g., gill slits, pattering of various transcription factors, post anal tail). To this end, we concentrated on the following: 1) Develop a comprehensive phylogenetic frame work based on traditionally used nuclear and mitochondrial genes. The first iteration of this work was published in 2009 with graduate student Cannon as the first author. This work is being expanded with recent collections made through collaborative efforts. 2) Phylogenetic analyses using a genomic approach with 454 and Illumina DNA sequencing have been a central activity of this award. At the time of writing this report, we are waiting for the last batch of data for analysis. Contrary to nuclear ribosomal data, genomic data indicated pterobranchs are sister to enteropneusts, and not nested within them. Our preliminary results as support the general placement of echinoderm groups based on traditional understanding. Broader Impacts In an effort to consolidate, distill, and present biological knowledge of extant hemichordates, a Specific Aim of this proposal is to organize and disseminate, via web-based outlets, sets of information on hemichordates appropriate for K-12, as well as researchers. This informational data based will go-live in 2012. In terms of personnel, a female graduate students and three undergraduates (2 female and 1 male) were trained as part of this proposal. Additionally, the PIs was active in teaching and mentoring undergraduates, graduate students and postdoctoral fellows, and actively encouraged engagement from underrepresented groups. Outreach by Halanych to several K-3 students (>200 students over course of award). Additionally he and his lab participates in events organized by the College of Science and Mathematics at Auburn. By using organized events, Halanych and the lab interact with several hundred students in a day in an education 'fair' type setting 2-3 times a year.