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.
Hemichordates are close relatives to echinoderms and are also distantly related to humans. Hemichordates are important to study because it is likely that they are the living animals that most closely resemble our long ago invertebrate ancestors (Brown et al. 2008). Funds from this grant allowed our lab at the University of Washington to study the number of different species of hemichordates that are found on the earth. First, we have updated all of the described 121 species of hemichordates on the World Register of Marine Species (WoRMS). www.marinespecies.org/aphia.php?p=taxdetails&id=1818 We have also continued to collect and describe new hemichordate species, especially in Antarctica and the deep sea. We’ve published one paper on hemichordate phylogeny (Cannon et al. 2006) and have a second one in preparation with many more species. We’ve used a special kind of gene, a very small molecule called microRNAs as a phylogenetic character to show that all of the enteropneust worms are related to each other (Peterson et al. 2013). We have discovered and documented that some hemichordates, the ptychoderid worms, have the ability to completely regenerate both halves of their bodies if chopped in half. We are continuing to study the molecular basis of this in order to understand aging and regeneration in humans (Rychel and Swalla, 2008; 2009). We’ve trained a number of excellent scientists with this grant money! Dr. Noa Shenkar was a Postdoctoral Fellow in the Swalla Lab at the University of Washington, who now has her own lab in the Department of Zoology at Tel Aviv University in Israel. Noa studied different species of ascidians and hemichordates and learned how to distinguish the different species from one another. www.tau.ac.il/lifesci/departments/zoology/members/shenkar/shenkar.html Amanda Rychel received her Ph.D. in the Swalla Lab and went on to Postdoctoral work in Dr. Keiko Torii’s lab, also at the University of Washington. Amanda later worked at Stratos Genomics a Seattle Biotech start-up company. Joie Cannon will soon receive her Ph.D. in the Halanych Lab at Auburn University. She has been trained as an expert in hemichordate identification, systematics and phylogenetics. http://gump.auburn.edu/halanych/lab/Cannon.htm Shawn Luttrell was an undergraduate, working in the Swalla Lab when she published a paper describing the development of the hemichordate neural tube (Luttrell et al. 2012). Shawn is currently a first year graduate student in the Swalla Lab, continuing her work on hemichordate development and regeneration. Shawn just received a prestigious three year NSF Predoctoral grant for her research on hemichordates! Brown, F.D., Prendergast, A. and Swalla, B.J. (2008) Man is but a worm:Chordate Origins. Genesis 46: 605-613. Cannon, J.T., Rychel, A.L., Blasczyk, H., Halanych, K.M. and Swalla, B.J. (2009) Molecular phylogeny of Hemichordata. Mol. Phylo. Evolution 52: 17–24. Luttrell, S., Konikoff, C., Byrne, A., Bengtsson, B., and Swalla B.J. (2012) Ptychoderid hemichordate neurulation without a notochord. Integrative Comparative Biology 52 (6): 829-834. Peterson, K. J., Su Yi-H., Arnone M. I., Swalla B. J., and King B. (2013) microRNAs support the monophyly of enteropneust hemichordates. J. Exp. Zoolog. B Mol. Dev. Evol. 9999B:1–7. Rychel, A.L. and Swalla, B.J. (2008) Anterior regeneration in the hemichordate, Ptychodera flava. Develop. Dyn. 237 (11): 3222-3232. Rychel, A.L. and Swalla, B.J. (2009) Stem cells and regeneration in hemichordates. In: Marine Stem Cells, Valeria Matranga and Baruch Rinkevich, ed. Springer Publishing. pp. 245-265.
