Morphological dynamics in the foraging apparatus of a deposit feeding marine bivalve:phenotypic plasticity and heritable effects

1. Design considerations dictate that systems work most efficiently when the separate components have processing capacities adjusted to each other, a principle known as symmorphosis. Adjustments in response to a variable environment are most likely to occur at the interface between the environment and integrated systems. In deposit-feeding bivalves, the interface of the alimentary canal with the foraging environment consists of a siphon (intake), gills (flow generation) and palps (particle sorting).2. Among European populations of the Baltic Tellin, Macoma balthica, the gill-to-palp mass-ratio was positively correlated with the foraging environment, characterized by median grain size of the ambient sediment (R = 0.71).3. In laboratory-reared M. balthica gill-to-palp mass-ratio responded plastically to changes in ambient sediment characteristics, resulting in large ratios in coarse sediment and small ratios in fine sediment.4. In a common garden experiment, relative differences in gill-to-palp mass-ratios of laboratory-reared M. balthica from four populations appeared similar to those in the field, indicating a heritable component to the variation in integrated organ systems.5. Phenotypically plastic adjustments ensure a close match between the integrated system of the alimentary canal to the local foraging environment. Heritable variation among populations may reflect different selective optima related to consistent differences in the environment between the populations.