Digestive plasticity of the marine benthic omnivore Nereis virens

We investigated plasticity in the digestive chemistry of the omnivorous mar ine benthic polychaete Nereis virens. We sought to compare the previously o bserved variability among species (genotypic plasticity) versus the variabi lity within a species (phenotypic plasticity) in response to changes in die t. We found statistically significant changes in enzyme activities between worms given carnivorous versus detritivorous diets. These changes were smal ler in magnitude than the among-species range, but consistent in direction. The surface tension of the gut fluid was largely unaffected by diet. Howev er, the presence of surfactant micelles was closely linked to the presence of sediment in the diet. These results suggest that sediment ingestion indu ced the introduction of high concentrations of surfactants into the gut lum en, perhaps related to the adsorption of digestive agents and products onto the mineral matrix. In the context of the among-species trends found by Ma yer et al. (Digestive environments of benthic macroinvertebrate guts: enzym es, surfactants and dissolved organic matter. J. Mar. Res. 1997;55(4):785-8 12.), Nereis virens shows greater phenotypic plasticity in its surfactant s ecretion than in its enzymatic response to varying food types. (C) 1999 Els evier Science B.V. All rights reserved.