Meeting Abstract

S1.5  Monday, Jan. 4  Early deuterostome origins of the vertebrate head PANI, A; DARRAS, S; ARONOWICZ, J; LOWE, C J*; University of Chicago; IBDML-CNRS – Université de la Méditeranée; University of Chicago; University of Chicago clowe@uchicago.edu

The early evolution of chordates has long been a subject of intense debate in zoology, and despite over one hundred years of comparative biology, there is still little consensus on the early events in deuterostome evolution that led to the establishment of the chordate body plan. This lack of consensus is largely due to the vast morphological disparity between the major adult body plans of the major deuterostome phyla, and a poor early fossil record. Developmental genetics has recently provided a new influx of data that can be used to readdress issues of chordate origins. As an out-group to the chordates, hemichordates are a very promising group for addressing hypotheses of chordate origins. We have been investigating the role of secreted proteins, with conserved early developmental roles in neural plate polarization and the establishment of the vertebrate head, during the development of the hemichordate Saccoglossus kowalevskii. We have revealed considerable developmental similarities in early patterning between the vertebrate head and the anterior of the hemichordate body plan, despite the morphological disparities between the two groups. Surprisingly, the extent of the similarities between hemichordates and vertebrates are far more extensive than between ascidians and vertebrates, or amphioxus and vertebrates, and suggest that the early chordate lineages have lost some of the ancestral developmental complexity of head patterning. It also implies that many of the developmental innovations of head development, previously attributed as vertebrate innovations, evolved far deeper in deuterostome evolution, and were not coupled to vertebrate morphological innovation.