Transitional chordates and vertebrate origins: Tunicates

摘要: The Origin of Chordates has fascinated scientists from the time Charles Darwin's publication "Descent Man" in 1871. For over 100 years, it was accepted that chordates evolved tunicates, our sessile invertebrate sister group. However, genomic and embryonic analyses have shown lancelets a body plan genome much more like vertebrates than do tunicates. In 2000, we proposed worm-like hypothesis chordate origins, studies past 20 years supported this hypothesis. This contends deuterostome ancestor worm-like, with gill slits, very chordate. contrast, tunicates derived adult independently. Here, review current understanding phylogeny supporting evidence for relationships within each phylum. Then discuss origins to support it. We explore some evolutionary changes ascidians made their key gene regulatory networks been elucidated Ciona. Finally, end insights gained studying tailless 30 years. We've found differentiation genes, at networks, become pseudogenes nonfunctional, even though they are still expressed ascidians. expect eventually these will not be ascidian larval is abandoned, leaving embryo develop directly into an adult.