Meeting Abstract

S3-1.5  Wednesday, Jan. 4  Streblospio benedicti (Spionidae, Annelida) as a model organism for the study of larval evolutionary transitions SCHULT, N.*; MCHUGH, D.; Colgate Univ.

Streblospio benedicti represents a rare case of poecilogony and is an ideal model for the integration of approaches to study evolutionary transitions in larval development mode of marine invertebrates. S. benedicti is a small, tube-dwelling worm found in dense populations in mudflats along the east coast of North America and the southern Californian coastline. Females either produce numerous small eggs that develop as planktotrophic larvae that spend up to three weeks in the plankton, or fewer large eggs that have no requirement to feed during their abbreviated development. Ecological, quantitative genetic, functional morphological, and phylogeographic work over the past three decades has set the stage for understanding developmental mode transitions by integrating knowledge from multiple levels, from macrohabitat to molecular, in this species. Tools are now available to investigate the genetic architecture shaping the two developmental morphs. We report our characterization of an EST screen for S. benedicti and our isolation of regulatory genes associated with gut regionalization (e.g., Fox and GATA). Using segmental muscle bands as reference points for comparable stages between the two larval forms, our whole mount in situ hybridization experiments are revealing similarities and differences in gene expression patterns between the small-egg larvae that must feed early in development and the large-egg larvae that do not require a functional gut until later in development. We hope our work with S. benedicti, a single poecilogonous species, will inform our general understanding of interspecific developmental mode transitions that have occurred repeatedly in marine invertebrate taxa.