INDUCIBLE COLONY FORMATION WITHIN THE SCENEDESMACEAE: ADAPTIVE RESPONSES TO INFOCHEMICALS FROM TWO DIFFERENT HERBIVORE TAXA¹

Abstract

We studied the occurrence of colony formation within 40 different strains of Scenedesmaceae (Chlorococcales, Chlorophyta) in response to grazing-released infochemicals from the herbivorous zooplankters Brachionus calyciflorus Pallas (Rotifera) and Daphnia magna Strauss (Cladocera). With the exception of two strains, all strains showed similar responses to both B. calyciflorus and D. magna infochemicals, either no response or inducible colony formation. Colony size was found to increase with B. calyciflorus infochemical concentration and could be described by a sigmoid function. The increase in colony size was more pronounced in the Scenedesmus species tested than in Desmodesmus species, which was probably due to higher threshold infochemical concentrations for colony induction in Desmodesmus. Therefore, the adaptivity of colony formation to the herbivory threat only holds above the threshold concentration for colony induction and as long as maximum colony size has not been attained. Taking this into account, our results suggest that inducible colony formation is a common adaptive response of many Scenedesmaceae to the threat of herbivory.

Influence of Daphnia infochemicals on functional traits of Microcystis strains (Cyanobacteria)

“…Interstrain variability in growth rate and colony formation as reaction to zooplankton infochemicals was also reported in Scenedesmus (Lürling, 1999;Verschoor et al, 2004). Although this was not the focus of our study, the influence of zooplankton infochemicals on traits of a particular Microcystis strain might also vary with culture conditions, as it has been shown that several environmental factors influence growth rate and microcystin production (Lukač & Aegerter, 1993;Sivonen & Jones, 1999;Wiedner et al, 2003).…”

“…In particular, the influence of zooplankton infochemicals on the morphology of the closely related green algae Scenedesmus and Desmodesmus has been intensively studied (e.g. Hessen & van Donk, 1993;Verschoor et al, 2004). The presence of infochemicals from grazers has been shown to induce changes in cell size, colony formation and spine formation in a range of species from both genera.…”

Invited Review - Fight on Plankton! or, Phytoplankton Shape and Size as Adaptive Tools to Get Ahead in the Struggle for Life

“…In contrast, filtrate from carnivorous zooplankton species does not induce colonies . This suggests that inducible colony formation is a general response to herbivory (Verschoor et al, 2004a; chapter 2), and not a response to any specific herbivore. An interesting question remains whether the algae respond to some general algal chemicals or to species-specific latent alarm pheromones released by the algae (cf.…”

“…It is therefore likely that in the absence of variable selection pressure by herbivorous zooplankton, the ability to induce colonies can be lost, as a result of ÂhiddenÊ costs for maintenance of the ability of colony induction. This could also imply that the infochemical threshold concentration required to induce colony formation in certain laboratory strains (Verschoor et al, 2004a; chapter 2) might be much higher compared to conspecifics under field conditions that are exposed to varying intensities of herbivory.…”

“…Nevertheless, there are plenty of species that do not possess inducible defences, and species with and without inducible defences usually cooccur within the same system. Already within the group of Scenedesmaceae alone, there is considerable variability in both morphology and the occurrence of inducible colony formation, even within the same species (Verschoor et al, 2004a;chapter 2). This can be understood from the fact that many different factors affect an organismÊs morphology.…”