S17-01 The evolution of early embryonic patterning and segmentation in arthropods

Did segmented body plans evolve just once, or repeatedly among the animals? This question has become all the more controversial, now that molecular phylogenetic trees make it clear that the three major clades of segmented animals, vertebrates, annelids and the pan-arthropoda, each lies within a different major clade of the animals. If we are to have any hope of understanding the origins of segmentation from developmental studies, we need to understand just how diverse the mechanisms of segmentation are within individual phyla. To do this, we need to study a diversity of early radiating lineages, and not just the more convenient model species. I will present our work on the early development of the onychophoran Euperipatoides kanangrensis and the centipede Strigamia maritima (Myriapoda: Geophilomorpha). Onychophorans are the sister phylum to the arthropods within the pan-arthropoda, and centipedes represent one of the basally diverging lineages within the phylum arthropoda. Both are therefore of importance for understanding the evolution of embryonic patterning mechanisms within the arthropods, and more widely among the animals, but little is known about the molecular mechanisms of development in either group. Our studies suggest that some aspects of early development are broadly conserved (e.g. aspects of head patterning and Hox gene registration), while others are much more divergent (e.g. early axis specification and the mechanisms of segment generation).