Abstract-Phlorotannins are ubiquitous secondary metabolites in brown algae that are phenotypically plastic and suggested to have multiple ecological roles. Traditionally, phlorotannins have been quantified as total soluble phlorotannins. Here, we modify a quantification procedure to measure, for the first time, the amount of cell-wall-bound phlorotannins. We also optimize the quantification of soluble phlorotannins. We use these methods to study the responses of soluble and cell-wall-bound phlorotannin to nutrient enrichment in growing and nongrowing parts of the brown alga Fucus vesiculosus. We also examine the effects of nutrient shortage and herbivory on the rate of phlorotannin exudation. Concentrations of cell-wall-bound phlorotannins were much lower than concentrations of soluble phlorotannins; we also found that nutrient treatment over a period of 41 days affected only soluble phlorotannins. Concentrations of each phlorotannin type correlated positively between growing and nongrowing parts of individual seaweeds. However, within nongrowing thalli, soluble and cell-wall-bound phlorotannins were negatively correlated, whereas within growing thalli there was no correlation. Phlorotannins were exuded from the thallus in all treatments. Herbivory increased exudation, while a lack of nutrients had no effect on exudation. Because the amount of cell-wall-bound phlorotannins is much smaller than the amount of soluble phlorotannins, the major function of phlorotannins appears to be a secondary one.

We propose that variation in the responses of carbon-based secondary compounds to fertilization in woody plants has a biosynthetic cause. The synthesis of phenylpropanoids and derived compounds (e.g., condensed tannins) competes directly with the synthesis of proteins, and therefore with plant growth, because of a common precursor, phenylalanine. In contrast, the biosynthesis of terpenoids and of hydrolyzable tannins proceeds presumably without direct competition with protein synthesis. Therefore, accelerated plant growth induced by fertilization may cause a reduction in concentrations of phenylpropanoids but may affect less or not at all the levels of other classes of secondary compounds. A meta-analysis based on fertilization experiments with 35 woody plant species supported the predicted differences: fertilizing significantly decreased concentrations of phenylpropanoids but not of terpenoids or hydrolyzable tannins.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. British Ecological Society is collaborating with JSTOR to digitize, preserve and extend access to Functional Ecology. Summary 1. We studied how the outcome of simulated herbivory on the leading shoot of young Scots pine (Pinus sylvestris) depended on the extent and timing of the damage, and on whether the damaged part was physiologically a sink (bud) or a source (needle). In addition we studied how the position of the shoot in relation to the damaged shoot affected the outcome of treatments. 2. Damage to needles had either growth-stimulating or growth-suppressing effects, whereas damage to buds had a positive effect on growth. 3. Needles and shoots were able to compensate for a significant amount of defoliation but not for complete defoliation: 100% but not 50% defoliation of the leader shoot significantly decreased average needle mass and length, and to a lesser extent shoot size. 4. The impact of defoliation depended on the relative position of the shoot and on the timing of defoliation. The growth of new shoots, which were situated 'above' the defoliated shoot, was reduced. This was most apparent in the trees defoliated late in the season. The growth of shoots that were situated 'below' the defoliated shoot was increased. 5. The results show that the responses of Scots pine to simulated herbivory are dependent on the within-tree regulation of growth and that seemingly minor differences in the methods of simulated herbivory may explain the great variability in the results obtained in studies of herbivory-induced responses in trees. Functional Ecology (1994) 8, 631-639 This content downloaded from 150.135.239.97 on Tue, 29 Sep 2015 07:16:08 AM All use subject to JSTOR Terms and Conditions American Naturalist, 139, 870-882. Bryant, J.P., Chapin III, F.S. & Klein, D.R. (1983) Carbon/nutrient balance of boreal plants in relation to vertebrate herbivory. Oikos, 40, 357-368. Bryant, J.P., Heitkonig, I., Kuropat, P. & Owen-Smith, N. (1991) Effects of severe defoliation on the long-term resistance to insect attack and on leaf chemistry in six woody species on the southern African savanna. American Naturalist, 137, 50-63.This content downloaded from 150.135.239.97 on Tue, 29 Sep 2015 07:16:08 AM All use subject to JSTOR Terms and Conditions

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.

Responses of Pinus sylvestris branches to simulated herbivory are modified by tree sink/source dynamics and by external resources T. HONKANEN,* E. HAUKIOJA* and V. KITUNEN † *Laboratory of Ecological Zoology, Department of Biology, University of Turku, FIN-20014 Turku and †Finnish Forest Research Institute, P. O. Box 18, FIN-01301, Vantaa, Finland Summary 1. It is claimed that the quality of foliage following defoliation depends on carbon/nutrient balance of the tree. To study the importance of sink/source regulation for the quality of foliage, as well as for its quantity, Pinus sylvestris trees were defoliated and fertilized both in southern Finland and at the tree line in northern Finland. 2. The pattern of defoliation in a shoot was more decisive for quantitative changes in new foliage than its extent: removal of similar amounts of foliage from different branch parts led to different outcomes. 3. Defoliation of 50% spread evenly within a shoot, or applied to the basal part of a shoot only, did not alter production of new foliage, whereas defoliation applied to the apical part of a shoot decreased the mass and length of needles in the new shoot. Defoliation of apically located 1-year-old needles of the branch leader shoot, but not of 2-year-old ones, significantly reduced the mass and length of needles in new shoots. 4. These results are consistent with the explanation that damage alters the ability of shoots and branches to form strong meristematic sinks and that sink strength determines the ability of these meristems to draw resources from the common pool of the tree. 5. Defoliation of the main photosynthate source lowered concentrations of the fructose and glucose, indicating shortage of carbon. However, whole-tree defoliation did not affect the concentrations of individual foliar sugars. 6. Traits describing pine shoot growth correlated negatively with foliar phenolic concentrations but not with concentrations of other secondary compounds. Concentrations of foliage phenolics consistently increased after defoliation, while terpenoids, putatively the main class of defensive compounds in Scots Pine, did not respond to defoliation. Defoliation of a branch or a whole tree had only slight effects on the concentrations of fibre, mono-and sesquiterpenes, resin acids or nitrogen. 7. Likewise, fertilization significantly increased the concentration of some sesquiterpenes only in pine foliage. Whole-branch defoliation and fertilization together had no effect on the concentration of fibre or nitrogen in pine foliage. 8. Altogether, the amount of foliar biomass removed, nutrients or carbon did not explain in any consistent way the qualitative changes in the pine foliage. Instead, results were consistent with simple physiological dependence of foliar traits on sink strength. Production of terpenoids reflected increased sink strength, but the production of phenolics was negatively correlated with sink strength. 9. The difference between shoot growth characteristics and foliage concentrations of phenolics and, on the...

The evolutionary hypotheses on plant-herbivore interaction assume that plant secondary compounds, such as the phlorotannins of brown algae, function as feeding deterrents for herbivores. We studied the effect of seaweed quality on the feeding preferences and performance of the isopod Idotea baltica. We offered I. baltica 6 species of algae, abundant in the Fucus vesiculosus belts where this mesograzer lives, in simultaneous preference tests. The tests were conducted both with natural algae and with artificial food made of freeze-dried and powdered algae of the same species. We found clear feeding preferences among the natural algae: the order of decreasing preference was F. vesiculosus > Dictyosiphon foeniculaceus > Elachista fucicola > Pilayella littoralis > Enteromorpha intestinalis > Ceramium tenuicorne. The preferences in the test with artificial food, however, did not parallel those with natural algae, suggesting that the chemical quality of algae is not the major determinant of feeding preferences. Furthermore, performance of isopods when reared on a diet of single algal species did not match the feeding preferences of natural algae: the most preferred brown alga provided poor growth rate. Surprisingly, the more phlorotannin a seaweed species contained, the more it was preferred by I. baltica. Moreover, the assimilation efficiency of soluble sugars was generally high when isopods fed on brown algae, and in the 2 species richest in phlorotannins it was not correlated with the phlorotannin concentration of the algal individual. In contrast to the conventional assumption of the defensive function of phlorotannins, this study shows that phlorotannins in seaweeds do not function as feeding deterrents to I. baltica. Instead, this herbivore readily feeds on phenolic-rich host plants, which, however, carries a cost in terms of decreased growth rate. We suggest that feeding preferences and habitat choice behavior evolve together; habitat structure, in terms of predation avoidance, and the spatiotemporal stability of the host algae are more important factors selecting for feeding preferences in mesoherbivores than the chemical composition of algae.

Inducible resistance in plants is a defense strategy for avoiding the negative consequences of herbivory on plant fitness. Since resistance is costly, the induction of resistance may depend on resource availability. Resource-based plant -herbivore hypotheses predict that the cost of producing carbon-based defensive metabolites will be higher when an excess of nutrients is available for growth. We tested experimentally the effect of nutrient availability on the occurrence, duration and within-alga spread of inducible resistance in the brown alga Fucus vesiculosus L. Based on feeding preference bioassays using the herbivore Idotea baltica (Pallas), simulated grazing of F. vesiculosus caused a clear, rapid, induced resistance that disappeared after 10 to 38 d. Furthermore, the induction of resistance does not spread to neighboring fronds or to growing tips above the point of simulated grazing. Induced resistance against isopod grazing, however, was not explained by increased production of phlorotannins, despite their putative role in the defense against herbivory. Phlorotannin production responded most strongly to nutrient enhancement, which reduced the phlorotannin concentration of the alga. Nutrient enhancement, however, did not affect the induction of resistance. The occurrence of induced resistance together with the lack of correlation between the phlorotannin concentration and the food preferences of herbivores imply that I. baltica is not deterred by the total quantity of phlorotannins; there may, however, be other, as yet unknown, rapidly inducing substances in F. vesiculosus that are capable of functioning as feeding deterrents to isopod grazers. Resistance may also arise as a side-effect of substances with a functional role, for instance in wound-healing processes. The localized nature and short duration of such deterrence imply that it may be inefficient as a general defense against herbivory, but may benefit the alga by dispersing future damage within the individual and avoiding the breakage of whole fronds.

Directional selection for plant traits associated with resistance to herbivory tends to eliminate genetic variation in such traits. On the other hand, balancing selection arising from trade‐offs between resistance and growth or spatially variable selection acts against the elimination of genetic variation. We explore both the amount of genetic variation and variability of natural selection for growth and concentration of phenolic secondary compounds, phlorotannins, in the brown alga Fucus vesiculosus. We measured variation in selection at two growing depths and two levels of nutrient availability in algae that had faced two kinds of past growing environments. Genetic variation was low for growth but high for phlorotannins. The form and strength of selection for both focal traits depended on the past growing environment of the algae. We found strong directional selection for growth rate in algae previously subjected to higher ultraviolet radiation, but not in algae previously subjected to higher nutrient availability. Stabilizing selection for growth occurred especially in the deep growing environment. Selection for phlorotannins was generally weak, but in some past‐environment–current‐environment combinations we detected either directional selection against phlorotannins or stabilizing selection. Thus, phlorotannins are not selectively neutral but affect the fitness of F. vesiculosus. In particular, there may be a fitness cost of producing phlorotannins, but the realization of such a cost varies from one environment to another. Genetic correlations between selective environments were high for growth but nonexistent for phlorotannins, emphasizing the high phenotypic plasticity of phlorotannin production. The highly heterogeneous selection, including directional, stabilizing, and spatially variable selection as well as temporal change in selection due to responses to past environmental conditions, probably maintains a high amount of genetic variation in phlorotannins. Such variation provides the potential for rapid evolutionary response of phlorotannins under directional selection.