Phenotypic flexibility and physiological tradeoffs in the feeding and growth of marine bivalve molluscs

Bivalve molluscs have a highly plastic feeding and growth physiology.The increasing availability of families artificially selectedfor faster growth has enabled physiological experiments to investigatethe genetic basis for variable rates of growth. Fast growthis achieved by a combination of increased rates of feeding,reduced metabolic rates and lower metabolic costs of growth.In at least one species there is a trade-off between growthin protein and the storage of lipids that are utilized in gametogenesis.Energy requirements for maintenance are also higher in slow-growingindividuals. Reduced costs of growth are due in part to increasedefficiencies of protein turnover. Nevertheless, high proteinturnover (and therefore high metabolic cost) may benefit fitnessin the later stages of gametogenesis. Faster feeding rates donot impair flexibility in feeding behavior which compensatesfor changes in the food environment. Both inter- and intra-speciesdifferences in feeding behavior are evident and suggest possibleconstraints imposed by faster feeding on the efficiency of selectionbetween food particles of different nutritional value.