Meeting Abstract

26.5  Wednesday, Jan. 4  Life History Evolution: Insights from Comparative Development and Gene Expression in Sipuncula BOYLE, M. J.*; RICE, M. E.; Smithsonian Marine Station at Fort Pierce, Florida

Marine invertebrate animals develop through some of the most diverse life history patterns on earth, but how those patterns evolve is a mystery. We are in search of evidence that may reveal how direct, lecithotrophic and planktotrophic developmental modes diverged in Sipuncula, a clade of non-segmented, coelomate marine worms with a unique larval form, the pelagosphera. Our models include: Phascolion cryptum, which develops directly from an embryo to the vermiform stage, Themiste alutacea, which develops indirectly through lecithotrophic trochophore and pelagosphera larvae, and Nephasoma pellucidum, which develops indirectly through a lecithotrophic trochophore and a planktotrophic pelagosphera larva. Confocal laser scanning micrographs reveal variation between these species in the position and timing of organ system formation, including the presence or absence of a buccal organ, terminal organ, trochal bands or functional gut. Molecular evidence across Metazoa suggests that such variation is regulated by the expression of transcription factors and cell signaling pathways. We isolated fragments of developmental regulatory genes (foxA, blimp-1, brachyury, wingless), including three Parahox genes (gsx, xlox, cdx) from each sipunculan species. The foxA gene is expressed in the developing esophagus and endoderm of N. pellucidum and P. cryptum, and the wingless gene is expressed in ectoderm of the digestive system, posterior pole, and transition between the introvert and trunk of the pre-vermiform stage of P. cryptum. The Parahox genes are expressed in the developing gut of N. pellucidum, and both the nervous system and gut during development of P. cryptum. Additional patterns for all three species are in progress, and they will be presented in the context of life history evolution.