Regulation of anti‐herbivore defence by Fucus vesiculosus in response to various cues

Abstract

Summary 1We examined whether the marine macroalga Fucus vesiculosus induces defences against herbivory and, if so, which factors trigger this induction. In addition, we assessed whether induced defences are reduced after consumption stops. 2 Induced effects were measured as changes in palatability rather than changes in the chemistry of the algae. We also tested for reductions in growth rate to determine whether induced defence incurs metabolic costs. 3 We tested whether direct grazing, feeding on neighbouring plants, clipping and presence of a non-grazing herbivore could trigger induction. The isopod Idotea baltica and the gastropod Littorina littorea were used as herbivores. 4 Both direct feeding of I. baltica and feeding on neighbouring plants induced chemical defence in F. vesiculosus , whereas the snail L. littorea only induced defence by direct grazing. Simulated herbivory (clipping), or the presence of herbivores without grazing, did not lead to defence induction. All induced defences were reversed within 2 weeks of consumption ending. 5 Thus, F. vesiculosus differentiates between physical damage and natural herbivory. Furthermore, feeding by I. baltica on F. vesiculosus releases signals that trigger neighbouring Fucus individuals to induce defence. 6 We found no evidence that metabolic costs incurred as a consequence of induced defence were sufficient to lead to growth reduction. 7 This algal species demonstrates defence plasticity (i.e. induction and reduction of anti-herbivore defences 'on demand'), with the response depending on both grazer identity and grazing pattern matter.

Herbivore-induced defence response in the brown seaweedFucus vesiculosus(Phaeophyceae): temporal pattern and gene expression

“…Defences were first detectable 18 days after onset of grazing. This timing differs from an isopod grazing period of 9-14 days that was required to induce defences in F. vesiculosus in previous studies (Rohde et al, 2004;Rohde & Wahl, 2008;Yun et al, 2012). Rohde & Wahl (2008) suggested the induction of defences was triggered by biomass loss rather than by the duration of grazing and proposed that a loss of 5-10% wet mass represents the threshold at which benefits of protection against grazing may outweigh defence costs in F. vesiculosus.…”

“…Furthermore, the ability to induce anti-herbivory traits in response to grazing by mesoherbivores has been repeatedly shown for different F. vesiculosus populations (e.g. Hemmi et al, 2004;Rohde et al, 2004;Long et al, 2007;Yun et al, 2007;Yun et al, 2012).…”

“…Regulation of genes involved in photosynthesis in Fucus vesiculosus after 15 and 18 days of isopod grazing. Identification of differentially expressed genes as well as calculation and interpretation of fold changes (FCs) as described for differences in food quality (see also Rohde et al, 2004;Long et al, 2007). Defences were first detectable 18 days after onset of grazing.…”

“…Previous induction experiments showed that differences in palatability between previously grazed and non-grazed seaweed pieces occurred within 9-14 days after onset of herbivory (Rohde et al, 2004;Rohde & Wahl, 2008;Yun et al, 2012) and were reduced within 2-4 days when grazing stopped (Rohde & Wahl, 2008). Thus, grazing pressure and seaweed responses may generally be promptly coupled.…”

Variability in grazer-mediated defensive responses of green and red macroalgae on the south coast of South Africa

“…Most references to inducible defences are restricted to the brown algae, particularly the fucales (Van Alstyne 1988;Cronin and Hay 1996;Pavia and Toth 2000;Toth and Pavia 2000;Sotka et al 2002;Taylor et al 2002;Rohde et al 2004;Macaya et al 2005), with two recent reports of chemical defences in red algae (Weidner et al 2004;Ceh et al 2005). We found grazing-mediated changes in palatability for three red algae and one out of the two green algae analysed.…”