Abundance of Food Affects Relative Size of Larval and Postlarval Structures of a Molluscan Veliger.

Veliger larvae of mollusks were predicted to develop a larger velum relative to the larval shell when reared with scarce food. The functional consequences of such developmental plasticity would be (1) greater maximum capacity for capturing particles when food is scarce and (2) greater growth of structures retained in the postlarva when food is abundant. The hypothesis was tested by rearing veligers of the oyster Crassostrea gigas at high (near satiating) and low (growth limiting) concentrations of food. Veligers at the measured shell lengths (>200 {mu}m) had significantly larger velar lobes and longer prototrochal cilia than veligers reared in low concentrations of food. An analogous response to food levels (relatively longer ciliated band when food is scarce) has now been found for larvae as disparate as oyster veligers and sea urchin plutei. These observations suggest that functionally similar examples of developmental plasticity in the growth of larval parts have evolved more than once and may be widespread. An alternative interpretation is that differential mortality or growth in a genetically heterogeneous batch of oyster larvae results in advanced veligers of different forms at different concentrations of food. Both interpretations suggest an adaptive advantage to growing a larger apparatus for clearing particles from suspension when food is scarce and shifting materials to growth of postlarval structures (shell and associated structures) when food is abundant.