The effects of phloroglucinol on Tegula herbivory
Primary producer’s strategies for defending themselves against herbivores has manifested in many ways. Chemical defense is one strategy that many plants have utilized to become less palatable to herbivores. The production of secondary metabolites such as tannins in terrestrial plants and phlorotannins in marine algae are hypothesized to have a deterring effect on herbivore grazing. Phloroglucinol (1,3,5 - trihydroxybenzene) is the monomer of all phlorotannins found in brown algae (Division Phaeophyceae). The monomer can be arranged in a variety of different ways for a variety of functions. Research on the function of phloroglucinol as the active deterrent of herbivory has conflicting results. To address this, two snail species from the genus Tegula were used to determine if the presence of phloroglucinol reduced herbivory. We exposed Tegula funebralis, an intertidal species and Tegula pulligo, a subtidal species to experimental seaweed plates with varying concentrations of phloroglucinol. The two Tegula species were selected as closely related representatives from different tidal heights to see if habitat played a role in phloroglucinol tolerance. We measured consumption and preference of experimental plates with different concentrations of phloroglucinol. Consumption was measured directly and preference was determined using a Y-maze. Our study shows that there is no deterring effect of phloroglucinol on either of the two Tegula species. The function of phloroglucinol may not have any implications in defense against Tegula herbivores. The production of phlorotannins in kelp species could be a general stress response without a specific stressor activating the production, and chemical defense is likely carried out by many compounds.
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