Induced defences in marine and freshwater phytoplankton: a review

Abstract

Many organisms have developed defences to avoid predation by species at higher trophic levels. The capability of primary producers to defend themselves against herbivores affects their own survival, can modulate the strength of trophic cascades and changes rates of competitive exclusion in aquatic communities. Algal species are highly flexible in their morphology, growth form, biochemical composition and production of toxic and deterrent compounds. Several of these variable traits in phytoplankton have been interpreted as defence mechanisms against grazing. Zooplankton feed with differing success on various phytoplankton species, depending primarily on size, shape, cell wall structure and the production of toxins and deterrents. Chemical cues associated with (i) mechanical damage, (ii) herbivore presence and (iii) grazing are the main factors triggering induced defences in both marine and freshwater phytoplankton, but most studies have failed to disentangle the exact mechanism(s) governing defence induction in any particular species. Induced defences in phytoplankton include changes in morphology (e.g. the formation of spines, colonies and thicker cell walls), biochemistry (such as production of toxins, repellents) and in life history characteristics (formation of cysts, reduced recruitment rate). Our categorization of inducible defences in terms of the responsible induction mechanism provides guidance for future work, as hardly any of the available studies on marine or freshwater plankton have performed all the treatments that are required to pinpoint the actual cue(s) for induction. We discuss the ecology of inducible defences in marine and freshwater phytoplankton with a special focus on the mechanisms of induction, the types of defences, their costs and benefits, and their consequences at the community level.

Induction of domoic acid production in the toxic diatom Pseudo-nitzschia seriata by calanoid copepods

“…Similarly, Lürling (1998) observed that only exudates from Daphnia grazing on digestible food induced colony formation in S. acutus. Cues related to active feeding may thus be the most reliable indication of the risk of herbivory for phytoplankton (Van Donk et al, 2011), explaining why cues from actively grazing consumers may produce a stronger induction.…”

“…In addition to the potential cues released by the grazers, mechanical damage of the algae may signal the risk of grazing, especially when feeding is "sloppy", even if the message may not always be reliable since algae also lyse, e.g. due to attack by viruses (Van Donk et al, 2011). The effect of mechanical damage on the potential inducible defenses in phytoplankton has been rarely studied (reviewed in Van Donk et al, 2011;see Lampert et al, 1994;Lürling, 1998).…”

“…due to attack by viruses (Van Donk et al, 2011). The effect of mechanical damage on the potential inducible defenses in phytoplankton has been rarely studied (reviewed in Van Donk et al, 2011;see Lampert et al, 1994;Lürling, 1998). It is possible that the chemicals released by the grazers and the damaged cells interact to produce the potential signal that eventually induces the defense reaction in the phytoplankton (Van Donk et al, 2011).…”

“…The effect of mechanical damage on the potential inducible defenses in phytoplankton has been rarely studied (reviewed in Van Donk et al, 2011;see Lampert et al, 1994;Lürling, 1998). It is possible that the chemicals released by the grazers and the damaged cells interact to produce the potential signal that eventually induces the defense reaction in the phytoplankton (Van Donk et al, 2011). Indications that the presence of the copepods may enhance DA production in P. seriata were found by Tammilehto et al (2012), where the DA cell quota in P. seriata increased after 12 h in the presence of C. hyperboreus.…”

How do freshwater organisms cross the “dry ocean”? A review on passive dispersal and colonization processes with a special focus on temporary ponds

“…Petrusek et al, 2009). The seasonal cyclomorphosis in rotifers and cladocerans (Dodson, 1989) or the production of spines in phytoplankton (Van Donk et al, 2011) is commonly observed effect of inducible defences. Predators thus (i) select those organisms which have defensive phenotypes and (ii) alter their traits in different environments (Werner & Peacor, 2003), therefore decreasing the colonization success of those organisms with phenotypes more susceptible to predation 123 (Covich, 2010).…”