Marine Plant-herbivore Interactions

Résumé du livre

Seaweeds produce a diverse array of secondary metabolites that deter feeding by common marine herbivores. However, the defensive value of a compound is a specific function of compound structure and the herbivore species attacking the plant. The function of compounds cannot be predicted by structural class alone so it is inappropriate, for example, to lump terpenes as toxins and phlorotannins as digestibility reducers. The spatial and temporal distribution of secondary metabolites within cells, within plants, and between plants often vary in ways that are adaptive. Individual plants or plant portions that are at greatest risk are often best defended. Herbivore size, mobility, and life-history characteristics appear to be correlated with resistance to seaweed chemical defenses. Small relatively sedentary herbivores like some amphipods, polychaetes, and ascoglossans (mesograzers) often selectively consume seaweeds that are low preference foods for fishes and larger invertebrates. Compounds from these seaweeds deter feeding by larger herbivores but stimulate, or do not affect, feeding by several mesograzers. Although a few mesograzers sequester chemical defenses from their algal hosts, most are not highly specialized and appear to be advantaged indirectly by their close association with seaweeds that are not visited by their predators. A comparison of chemical defense in marine versus terrestrial communities suggests that (a) the assumption of a fundamental difference in the cost and function of qualitative vs quantitative defenses needs to be reevaluated, (b) the degree of feeding specialization in marine vs terrestrial communities may differ due to fundamentally different dispersal modes of common herbivores, and (c) true coevolution is unlikely between seaweeds and marine herbivores.