Meeting Abstract

S3-1.7  Wednesday, Jan. 4  Poecilogony in the polychaete Polydora cornuta: A potential polyphenism that requires decisions, decisions, decisions. GIBSON, G D; Acadia University

Poecilogonous species are wonderful organisms with which to investigate the mechanisms that underlie developmental decisions leading to phenotypic divergence. For example, broods of the spionid Polydora cornuta contain eggs that develop to one of three morphs. Most become non-developing nurse eggs, some develop into embryos that ingest nurse eggs (i.e., adelphophagy) and have accelerated development, and some develop into non-adelphophagous embryos that hatch as small, planktotrophic larvae. Thus eggs spawned within a single egg capsule have three potential fates: death (as a nurse egg), the fast-track (as an adelphophagic larva) or a slower course of development as a planktotrophic larva. Each path appears to involve an active developmental decision. Nurse eggs are activated at spawning but immediately enter apoptosis (e.g., TUNEL, Annexin V). Apoptosis was not detected until much later in embryos, suggesting a decision that involves an early onset of a common developmental process in nurse eggs. Adelphophagy begins in gastrulae suggesting an early onset of the ability to capture food by mouth in some young, versus the use of ciliary bands by planktotrophic larvae. Preliminary work suggests this divergence is influenced by histone modifications. Providing females with methyl releasers decreased histone methylation (e.g., H3K9me2) in maternal tissues, increased variance in nurse egg production and increased the percentage of adelphophagous young per capsule. Although preliminary, these results suggest that epigenetic processes, such as histone modifications, provide a mechanistic link between the environment and developmental decisions leading to alternate phenotypes of young.