VON DASSOW, M; Univ. of California, Berkeley: Does fluid flow control pattern formation in a colonial suspension feeder?

Biological fluid transport systems have many functions in different organisms, including gas exchange and feeding. To what extent does the flow through the system determine subsequent pattern formation of the system during an organism�s growth? Colonies of the bryozoan Membranipora membranacea possess a simple fluid transport system involved in suspension feeding. Seawater is pumped into the colony by a canopy of ciliated tentacular structures (lophophores) that capture food particles from the seawater. The seawater then flows under the canopy of lophophores and exits the colony at either the colony edge or at raised openings (chimneys) within the canopy of lophophores. Fluid flow influences the spacing of the chimneys, and sites of chimney formation correlate with sites of high excurrent flow at the canopy edge. To test whether high excurrent flow at the canopy edge induces chimney formation, I injected seawater under the canopy near the canopy edge. New openings in the canopy formed near the site of seawater injection more frequently than at control sites in the same colonies. Lophophores surrounding these new openings were raised above the rest of the canopy much like lophophores around normal chimneys. These results suggest that high excurrent flow speed can induce chimney formation. The way this fluid transport system functions may control pattern formation during its subsequent development.