Meeting Abstract
How do patterning mechanisms evolve when life cycles become more or less complex? Most marine invertebrates have a biphasic life cycle that includes a planktotrophic larval stage (indirect developers), while others develop directly into a small-scale version of the adult (direct developers). Little is known about how mechanisms that regulate early development are modified when evolutionary transitions between these two life history strategies occur. As a result, interpreting comparative developmental data from animals that have both distinct body plans and different life cycles is difficult. It is not uncommon for closely related species with morphologically similar adult stages to have contrasting life history strategies. These organisms give us an opportunity to determine whether axial patterning mechanisms differ between direct and indirect developers, independent of their adult body plan. Enteropneust hemichordates are divided into two clades. One of them comprises exclusively direct developers that form an adult without intervening larval stages. The other comprises indirect developers that develop through a tornaria larva with an extended planktonic period. Here we describe axial patterning mechanisms in an indirect-developing hemichordate from the genus Schizocardium. We show the expression patterns of transcription factors with known function in anteroposterior (AP) patterning in other deuterostomes, as well as preliminary data on the function of some of the main signaling pathways that establish AP and dorso-ventral polarity. We test whether these mechanisms are more similar to the direct-developing hemichordate Saccoglossus, which has a similar adult body plan but an abbreviated life cycle, or to echinoderms, which have highly derived adult body plans but similar larvae.
