Phlorotannin Allocation Among Tissues of Northeastern Pacific Kelps and Rockweeds

Abstract

Optimal defense theory (ODT) predicts antiherbivore defensive compounds will be allocated so that the most valuable or most susceptible tissues will be best defended. The growth-differentiation balance hypothesis (GDBH) predicts that defense allocation will be a result of trade-offs between growth and defense. Thus, these two theories predict opposite allocation patterns with respect to ''valuable,'' actively growing meristematic and reproductive tissues. ODT predicts that meristems and reproductive tissues should have higher defense levels than nonmeristematic vegetative tissues; the GDBH predicts the defense levels of meristems and reproductive tissues will be lower than vegetative tissues. We examined allocation patterns of phlorotannins in 21 species of kelps (Order Laminariales) and rockweeds (Order Fucales) from nine sites on the west coast of the United States to determine if allocation patterns better matched the predictions of ODT or the GDBH and to look for differences in allocation patterns among sites. Within-species differences in phlorotannin levels occurred in 10 of the 21 species examined. Meristems of both kelps and rockweeds had higher phlorotannin levels than nonmeristematic vegetative tissues, consistent with ODT. Phlorotannin levels in reproductive tissues of kelps were higher than vegetative tissues, but levels in reproductive tissues of rockweeds were lower than vegetative tissues, indicating that allocation strategies may follow taxonomic lines. Allocation patterns differed among sites in four of the 16 species collected from more than one site. Differences in allocation patterns among sites were usually changes in the ratios of phlorotannins in well-defended compared to poorly defended tissues, rather than changes in which tissues were well defended or poorly defended. We concluded that environmental variability can have large effects on the concentration of phlorotannins in algae but has limited effects on allocation patterns among tissues.

Chemical mediation of interactions among marine organisms

“…89 ' 101 In contrast, many of the larger kelps have higher levels of phlorotannins in actively growing parts (intercalary meristems), holdfasts, and stipes than in infertile, nongrowing tissue. 82 ' 95 ' 102 Cronin and Hay 89 and Cronin 79 offer an explanation for these differing patterns in seaweeds. Kelps and coenocytic green algae have more developed translocation systems than most other macroalgae, 103 which might mean that the elevated concentrations of secondary metabolites found in growing tissues were produced in differentiated tissues and transported there.…”

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

“…Phlorotannins are known only from brown algae (Phaeophyceae), where soluble phlorotannins can constitute up to 25% dry weight (e.g., Targett et al, 1992;Van Alstyne et al, 1999). They are suggested to have multiple ecological roles: some phlorotannins act as chemical defenses against herbivory (e.g., Steinberg, 1988;Targett and Arnold, 1998;Arnold and Targett, 2000;Pavia and Toth, 2000a) and as antifouling substances (Sieburth and Conover, 1965;Wikström and Pavia, 2004), although the evidence for this function is equivocal (Jennings and Steinberg, 1997).…”

“…Variation in the contents of soluble phlorotannins has also been found among different parts of algae. In actively growing meristems, soluble phlorotannins have often been found in lower concentrations than in older vegetative parts (Jennings and Steinberg, 1997;Van Alstyne et al, 1999).…”

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

“…Many hypotheses on chemical defenses (summarized in Cronin 2001;Pavia and Toth 2008) seek to explain the allocation of overall resources and defense metabolites in macroalgae. The growth-diVerentiation balance hypothesis (GDBH) predicts that actively growing and reproductive tissues are less defended because of lacking cell diVerentiation when compared to diVerentiated vegetative tissue (Herms and Mattson 1992), which has been discussed in former studies (Cronin and Hay 1996;Van Alstyne et al 1999). Nevertheless, highly diVerentiated large brown algae (e.g., Laminariales, Fucales) may translocate low molecular weight compounds (e.g., precursors of phlorotannins) among functionally diVerent tissues (Raven 2003), which makes predictions from the GDBH diYcult to test (see discussion in Cronin and Hay 1996).…”