Induction of toxin production in dinoflagellates: the grazer makes a difference
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The dinoflagellate Alexandrium minutum has previously been shown to produce paralytic shellfish toxins (PST) in response to waterborne cues from the copepod Acartia tonsa. In order to investigate if grazer-induced toxin production is a general or grazer-specific response of A. minutum to calanoid copepods, we exposed two strains of A. minutum to waterborne cues from three other species of calanoid copepods, Acartia clausi, Centropages typicus and Pseudocalanus sp. Both A. minutum strains responded to waterborne cues from Centropages and Acartia with significantly increased cell-specific toxicity. Waterborne cues from Centropages caused the strongest response in the A. minutum cells, with 5 to >20 times higher toxin concentrations compared to controls. In contrast, neither of the A. minutum strains responded with significantly increased toxicity to waterborne cues from Pseudocalanus. The absolute increase in PST content was proportional to the intrinsic toxicity of the different A. minutum strains that were used. The results show that grazer-induced PST production is a grazer-specific response in A. minutum, and its potential ecological importance will thus depend on the composition of the zooplankton community, as well as the intrinsic toxin-producing properties of the A. minutum population.
KeywordsAcartia tonsa Alexandrium minutum Centropages typicus Inducible defense Paralytic shellfish toxin Pseudocalanus sp.
We thank Maria Grazia Giacobbe for kindly providing the CNR AMIA5 strain of A. minutum. Financial support was provided by the Swedish Research Council Formas through contract 21.0/2003-1122 to HP, by MARICE (Marine Chemical Ecology—an interdisciplinary research platform at the Faculty of Sciences, Göteborg University, Sweden), and by the Wåhlström, Carl Trygger and Colliander Foundations. The study complies with current law.
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