Induction of phlorotannin production in a brown alga: defense or resource dynamics?

Abstract

Eränen, J. 2003. Induction of phlorotannin production in a brown alga: defense or resource dynamics? -Oikos 103: 640-650.Increase of phenolic secondary metabolites, phlorotannins, in brown algae due to gastropod grazing has been interpreted as an anti-herbivore adaptation. Here we tested whether such a response could be due to changes in truly available resources for the alga, not by the grazing activity of snails as such. We allowed two species of snails, Theodoxus flu6iatilis and Physa fontinalis to graze on Fucus 6esiculosus. These species feed on epibiota and particulate matter on the thallus but do not eat the thallus of F. 6esiculosus. We further simulated snail grazing by nutrient enhancement, removal of epibiota and by a combination of the two. Manipulations of nutrient and light availability revealed the crucial role of epibiota in mediating resource availability for F. 6esiculosus. Nutrient enhancement alone increased epibiota and decreased phlorotannins. Cleaning the thallus resulted in increased growth, and together with nutrient enhancement also in a trade-off with phlorotannins. Presence of T. flu6iatilis on the thallus induced phlorotannin production, a response differing from the simulations of snail grazing. However, we suggest that the increase in phlorotannins may not be an induced defense but rather a consequence of a specific way of resource manipulation by this snail species. T. flu6iatilis removes hyaline hairs that facilitate nutrient uptake. P. fontinalis did not remove hyaline hairs and the response of the alga to its grazing was similar to the treatment where we mechanically removed epibiota suggesting that cleaning of the thallus is the major mechanism how this snail species affects F. 6esiculosus. Genetic variation in phlorotannin concentrations highly exceeded the induced responses of simulated or real snail grazing. This casts doubt for the efficiency of induced phlorotannin production to act as a defense, but is not contradictory with the interpretation of phlorotannins responding to variation in resource availability.

Species-specific defense strategies of vegetative versus reproductive blades of the Pacific kelps Lessonia nigrescens and Macrocystis integrifolia

“…Finally, not all herbivores are deterred by phlorotannins (Jormalainen et al 2003), indicating that some species have adapted to tolerate or utilize these algal compounds (Targett and Arnold 1998;Pavia et al 1997;Jormalainen et al 2003). Variations in eVectiveness are even found at a biogeographic scale; the comparatively low polyphenol contents found in North American Phaeophycean have been found to deter a range of herbivores, but Australasian invertebrate herbivores are unaVected by high levels of phlorotannins (Steinberg and Van Altena 1992), which underlines the suggestion that phlorotannins have roles other than defense in these species.…”

CONTENTS OF SOLUBLE, CELL-WALL-BOUND AND EXUDED PHLOROTANNINS IN THE BROWN ALGA Fucus vesiculosus, WITH IMPLICATIONS ON THEIR ECOLOGICAL FUNCTIONS

“…While such a nutrient effect is often explained by an increase in growth at the expense of allocation to the production of soluble phlorotannins, this was not the case in our experiment, since growth rate was not affected. In throughflow mesocosms, nutrient enrichment commonly leads to increased growth of epibiota (Honkanen and Jormalainen, unpublished data;Jormalainen et al, 2003); this, in turn, causes shading and may thereby explain the decrease in phlorotannin production. As such, the dynamic behavior of soluble phlorotannins together with the relative stability of cell-wall-bound phlorotannins supports an approach that uses soluble phlorotannins as the basis for studying phlorotannin plasticity.…”

“…Variation in the contents of soluble phlorotannins is to a large extent genetic (Jormalainen et al, 2003), but variation in cell-wallbound phlorotannins has never been measured. Since soluble and cell-wall-bound phlorotannins were not positively correlated, higher production does not necessarily mean a thicker cell wall.…”

Stressed, but not defenceless: no obvious influence of irradiation levels on antifeeding and antifouling defences of tropical macroalgae

“…Hitherto, a few studies investigated whether environmental stress due to desiccation, unfavourable temperatures, nutrients, or light-limitation diminishes the production of secondary metabolites in macroalgal tissue and/or its susceptibility to herbivore grazing (Renaud et al 1990;Yates and Peckol 1993;Cronin and Hay 1996a;Pavia and Toth 2000;Jormalainen et al 2003;Heaven and Scrosati 2004;Dethier et al 2005;Scheibling et al 2008;Pansch et al 2009). These, however, produced ambiguous results and none of them were performed in tropical systems, where grazing pressure is higher than in temperate systems (e.g.…”