Meeting Abstract

31.1  Friday, Jan. 4  Deconstructing Deuterosomes: Before a Head SWALLA, B.J.; University of Washington, Seattle bjswalla@u.washington.edu

Deuterostomia consists of related phyla that display distinct adult body plans, so present an excellent group of animals to study the evolution of larval and adult body plans. Echinodermata, Hemichordata and Xenoturbellida make up the Xenoambulacraria, while the Chordata consists of the Cephalochordata, the Tunicata and the Vertebrata. Cephalochordates share large stretches of chromosomal synteny with the vertebrates, have a colinear Hox complex with 14 Hox genes and are sister-group to the vertebrates based on ribosomal and mitochondrial gene evidence. In contrast, tunicates have a highly derived adult body plan and are sister-group to the vertebrates based on analyses of concatenated protein sequences. Larval morphology, rRNA, mitochondrial analyses, concatenated protein sequences and the adult heart/kidney complex all support echinoderms and hemichordates as a monophyletic Ambulacraria, with radically different adult body plans. Hemichordate enteropneust worms share the chordate features of gill slits, a post-anal tail, and an endostyle, while echinoderms have lost all of these features. Cephalochordates and hemichordates share acellular cartilages in their gill bars made by similar gene networks, suggesting that the ancestral deuterostome also had gill bars and gill cartilages. Gill slits are found dorsally on the abdomen of hemichordates, suggesting that the enteropneust collar and proboscis are anterior structures that evolved very differently than the chordate head. Some fossil echinoderms, the carpoids, also have dorsal gill slits, but the slits and anterior structures have been evolutionarily lost in echinoderms. Body axes are determined by similar gene networks, but the later specification of tissues in these animals has evolved dramatically.