VON DASSOW, M; Univ. of California, Berkeley: Development of a fluid transport system: An example from colonial organisms

Systems that transport fluids through organisms are important for many functions (e.g. feeding, O₂ transport, etc). What are the relationships between the way fluid moves through a transport system and the system’s subsequent development? Fluid flow through the bryozoan Membranipora membranacea is readily visualized, so it is a good system in which to address this question. M. membranacea colonies are comprised of an array of individuals that have ciliated crowns of tentacles (lophophores) forming a canopy over the colony. The lophophores generate a water current from which they capture food particles. The water flows between the tentacles and then under the lophophores until it exits the colony, either at the colony edge or at gaps in the canopy (chimneys) where the lophophores lean away from each other and are held higher than other lophophores. Chimneys form at the growing edge of the colony, and injuries large enough to form an opening in the canopy can induce the surrounding lophophores to lean away from the opening, suggesting that chimneys might form at sites of high excurrent flow. Chimneys might result from differences between individuals in either growth or behavior. Experiments were conducted to determine the relationships between flow within the colony and chimney morphology. Particle tracking to measure flow speed at the colony edge indicated that chimneys formed at sites of high excurrent flow speed in some colonies. Individuals near chimneys are taller than individuals far from chimneys even after anesthetization, suggesting that the chimneys result at least in part from differences in growth between individuals.