Chemically induced anti-predator defences in plankton: a review

Abstract

Planktonic organisms exhibit diverse morphological, behavioural and life-history responses to the chemical presence of potential predators. Prey organisms have been found to sense such predators via predator-derived kairomones. The induced reactions are assumed to reduce predation risk and thus to be adaptive. Numerous studies have investigated various aspects of inducible defences in different crustaceans, in rotifers, planktonic ciliates and algae. As a first step, we summarise recent work on chemically induced anti-predator defences in morphology, life history and behaviour. Morphological defences have been found in a wide range of different plankton organisms and recent studies on predator-induced morphologies mainly addressed the question of costs for these changes. Life-history responses were mainly studied in cladocerans and several studies have recently addressed some novel topics, such as diapause induction and the influence of predator kairomones on hatching of resting stages. Behavioural anti-predator defences also have been found for several plankton species and are characterised by relatively fast induction times. We further identified four research directions in which substantial progress has been made recently: (I) The effects of simultaneous exposure to infochemicals from different predators and the consequences of a complex chemical environment. Some environmental contaminants, such as synthetic chemicals or heavy metals, have been found to potentially disturb natural chemical communication in aquatic predator-prey systems. (II) The influence of genetic variation on the reaction to infochemicals and its implications. Clonal differences have not only been found for the presence or absence of a certain trait but also with respect to the type of response. (III) The degree to which different types of responses to a specific kairomone are coupled. Recent studies underline the uncoupling of different anti-predator responses of which some have been considered to be coupled. (IV) Studies on the chemical properties and on the metabolic origin of predator kairomones. Substantial progress has been made recently, especially with respect to the identification of predator kairomones that are important for planktonic ciliates. The identification and isolation of kairomones are an important step towards studies addressing the consequences of predator-induced defences on the level of populations, communities and ecosystems. So far most studies have considered effects and consequences on the level of individual prey organisms and studies taking the consequences at higher ecological levels into account are rare.

Behavioral response of Lake Michigan Daphnia mendotae to Mysis relicta

“…Experiment 3 suggests that these chemicals are large enough to be removed by a 0.46-µm filter, as Mysis water that had been filtered through such a fine filter had little or no effect on Mysis vertical position. This may offer a clue into the identity and properties of the kairomones, which are not well-known or understood in invertebrate predator-prey systems (Lass and Spaak 2003). Note that Experiment 4 suggests that the cue is not associated with alarm signals from conspecifics (Pijanowska 1997) because D. mendotae responded to water that never contained conspecifics, but rather only contained Mysis previously fed D. mendotae.…”

“…Predator-induced changes in vertical position and diel migration timing of Daphnia and other zooplankton in both freshwater and marine systems have been well documented (Frost and Bollens 1992, Fortier et al 2001, Irigoien et al 2004, reviewed in Hayes 2003, and Lass and Spaak 2003. Typically, movement is in a direction that is adaptive and reduces predation risk.…”

Effects of temperature and the presence of benthic predators on the vertical distribution of the ctenophore Pleurobrachia pileus

“…Forward and Rittschof (2000) showed that in the reaction of crab larvae (Rhithropanopeus harrisii) to the presence of fish polysaccharides played a role, whereas the spiny lobster Panulirus argus used mixtures of different substances to discriminate between different predators (Fine-Levy et al 1989). In many other well-known examples of chemical communication the chemical structure of the substances involved remains unclear (Lass and Spaak 2003).…”

Grazer-induced changes in the desmid Staurastrum

“…Especially in the last decade, it has become increasingly clear that chemicals excreted by predators (kairomones) can influence a wide range of characteristics in their prey species. In aquatic environments, predator kairomones have been shown to affect morphology, life-history traits and behaviour of prey species (reviewed by Harvell, 1990;Larsson & Dodson, 1993;Lass & Spaak, 2003). These predator-prey communication links have been found throughout aquatic foodwebs.…”