BAYNE, B.L.*; Univ. Sydney, Australia: Phenotypic plasticity in component processes to growth in marine bivalves

Bivalve molluscs are highly plastic in their feeding behavior and the component processes of growth. A few examples will be discussed in the context of responses to changes in the food environment. Different species respond in different ways, but the common net result is a compensation for reduced food quality that maximizes metabolisable energy intake. Though not yet formally tested, plastic feeding behavior appears to be adaptive. Flexibility in feeding combines with metabolic plasticity to yield variability in rates of growth. Genotypic differences, between hybrids and their inbreds or between lines selected for faster growth and their wild conspecifics, are expressed in a number of these component processes, including differences in energy acquisition, allocation and metabolic efficiency. Again, different species may respond in different ways, but a common outcome is the existence of tradeoffs between body maintenance, growth and reproduction. There is growing evidence also of generalist/specialist tradeoffs in inter-species studies. In seeking to relate this physiological diversity to differences in fitness, our attention should focus now on the integrated features of energy intake and associated physiological tradeoffs, rather than the highly complex interplay between proximate processes.