Preliminary evidence that the feeding rates of generalist marine herbivores are limited by detoxification rates

摘要

Herbivores tend to increase feeding rate and fitness when consuming a mixed diet relative to a single diet. According to the detoxification limitation hypothesis (DLH), feeding choices and rates when confronted with chemically rich plants are determined by herbivore physiology, and specifically by the metabolic pathways that herbivores use to manipulate secondary metabolites. We tested two predictions of the DLH using two generalist herbivores, the urchin Arbacia punctulata and amphipod Ampithoe longimana. These herbivores have geographic ranges which overlap with brown seaweeds that produce diterpenes (Dictyota menstrualis, D. ciliolata) and a green seaweed that produces sesquiterpenes and diterpenes (Caulerpa sertularioides). As predicted by the DLH, herbivore consumption rates in no-choice feeding assays were limited by extract intake rates. This suggests an upper limit in the herbivores’ abilities to physiologically manipulate seaweed metabolites. Contrary to a second prediction of the DLH, urchins consumed equal amounts of foods coated with limiting concentrations of two seaweed extracts offered singly, as a mixture, or as a pairwise choice. This result suggests that secondary metabolites of these seaweeds are manipulated by a linked set of detoxification pathways. Improving our understanding of the mechanisms that underlie diet mixing depends on greater attention to the physiology of herbivore resistance to secondary metabolites.