Functional Consequences of Phenotypic Plasticity in Echinoid Larvae

Phenotypic plasticity in feeding structures has been described for several larvae of marine invertebrates, including four species of echinoids. In these echinoids, larvae grown with scarce food grow a longer ciliated band than larvae grown with abundant food. Such phenotypic plasticity may be functionally significant if longer ciliated bands permit higher feeding rates when food is scarce. We replicate an earlier result showing that larvae of a sand dollar, Dendraster excentricus, grow longer ciliated bands in culture with scarce food. We show that these larvae can capture suspended food particles at the tips of longer arms, and that longer ciliated bands result in higher maximum clearance rates. The maximum clearance rate is enhanced by this phenotypic plasticity both early and late in larval life. However, longer ciliated bands did not completely compensate for reduced food supply: larvae grown with scarce food needed more time to complete larval development and metamorphosed into smaller juvenile sand dollars relative to larvae grown with abundant food.