Geographic variation in seaweed induced responses to herbivory

Abstract

Recent work on European (Swedish and English) populations of Ascophyllum nodosum has detected inducible defenses in response to snail grazing that include a decrease in algal palatability and an increase in phlorotannin concentration, a class of potential chemical defenses. However, tests of induced responses in other A. nodosum populations are lacking and we thus have a limited understanding of how widespread such responses are in fucoid algae. We exposed a North American (Massachusetts) A. nodosum population to Littorina obtusata, the same snail species used in previous studies, and tested for the presence of inducible responses during 2 experiments. In contrast to European populations, the North American population of A. nodosum did not develop any such responses. Exposure to either direct grazing or just waterborne cues associated with grazing for 26 d failed to suppress the palatability of artificial foods made from seaweed tissues exposed to these treatments. In addition, exposure to grazer cues did not increase seaweed phlorotannin levels compared to controls. The lack of induced responses in the North American population cannot be attributed to tissue type or potential seasonal variation in inducibility because each of our 2 independent experiments tested for responses in 2 tissue types (apical tips and basal shoots) in both the winter and spring. Furthermore, consistent with European work, the North American population lacked obvious grazing damage at the time of collection, suggesting that the differences we observed were unrelated to recent history with grazers. Thus, our work and that of others indicates that A. nodosum displays considerable inter-population variability in its response to a single herbivore species.

Chemical cues induce consumer-specific defenses in a bloom-forming marine phytoplankton

“…First, interstrain differences could produce the differing responses; Tang's P. globosa strain (CCMP 1528) was isolated from the Galapagos Islands, whereas ours (CCMP 627) was isolated from the Gulf of Mexico. Strains may respond differently to grazers given the recent discoveries that P. globosa is a multispecies complex (36) and that inducible responses to grazers can be population-or strain-specific (37,38). Second, our design prevented new cue production after filtrate collection, whereas Tang's design allowed for continuous cue production.…”

Seaweed-mediated indirect interaction between two species of meso-herbivores

“…Long & Trussell 2007). For instance, previous research on a congeneric species to that used in the present study, Fucus radicans, has shown that it exhibits different adaptive traits regionally, due to restricted gene flow (Bergström et al 2005).…”

Risk recognition and variability in escape responses among intertidal molluskan grazers to the sun star Heliaster helianthus

“…The conditions for the evolution of inducible defenses have been amply investigated, but our understanding of variability of these responses, particularly over geographic scales, is still poor (Sanford et al 2003, Kishida et al 2007, Long & Trussell 2007). In the case of predators and their prey, although they typically coexist along large portions of their geographic ranges, often there are areas (e.g.…”