HODIN, Jason; Hopkins Marine Station: Expanding networks: a hypothesis for the evolution of metamorphosis
Metamorphosis is a more or less radical morphological transition between two multicellular phases in an organism's life cycle, often marking the passage from a pre-reproductive to a reproductive life stage. It generally involves major physiological changes and a shift in habitat, feeding mode, etc., and can be subdivided into a long-term phase that involves substantial morphological remodeling, and a shorter-term phase (“settlement” in marine invertebrates, "adult eclosion" in insects, fruiting body emergence in mushrooms) where the actual shift in habitat occurs. In most echinoderms (sea urchins, sea stars, sea cucumbers and their kin), these two phases are fairly distinct: at the end of larval development, an essentially fully-formed juvenile is present within the larval body. At settlement, this juvenile rapidly emerges. I will present data from several echinoderms outlining a core regulatory network: thyroid hormones regulate the morphogenetic transition from bilateral larva to pentameral juvenile (longer-term phase); thyroid hormones interact antagonistically with the NO repressive network regulating settlement (the shorter-term phase); and the transmission of environmental settlement cues to induce a physiological response involves multixenobiotic efflux transport activity. I will explore how this core regulatory network can be acted on by natural selection to suit the diverse ecological needs of disparate echinoderm larvae, and speculate on the ways that exposure to xenobiotic pollutants and other compounds might influence successful settlement of juveniles in the wild.