Grazer-induced changes in the desmid Staurastrum

Abstract

In aquatic environments, predator kairomones have been shown to affect morphology of prey species. Past work on the interaction between zooplankton and phytoplankton was based mainly on the Daphnia-Scenedesmus model. Algae of the genus Staurastrum can produce mucilage, causing cell clumping and settling out of the water column. These clumps are too large to be eaten by daphniids. Thus, we hypothesised that this may be a grazer defence. We investigated whether Daphnia magna induces the formation of mucus globules in Staurastrum, how this occurs, and if the formation of clumps inhibits growth in juvenile Daphnia. Eight strains of Staurastrum were used to check whether mucus extrusion is induced by the presence of Daphnia or possibly by a chemical excreted by Daphnia magna. None of the strains reacted to the presence of Daphnia water alone, animals had to be present to induce clumping. Mechanical action (gentle stirring) caused the same strains to clump. The ecological relevance of clumping was then investigated. The different Staurastrum strains were used as food in a growth experiment with ecologically relevant densities of neonates of Daphnia hyalina. These small daphniids did not cause the same clumping observed for Daphnia magna when present in experiments at high densities. We observed that juvenile daphniids grew less well on strains with larger cell size.

Morphological Response of Microcystis aeruginosa to Grazing by Different Sorts of Zooplankton

“…An effective way for algae to reduce the risk of being eaten is through an increase in size when necessary. Inducible colony formation found in present experiment and some other studies (Harvell, 1990;Luerling & van Donk, 1996Fialkowska & Pajdak-Sto´s, 1997, 2002Boraas et al, 1998;Pajdak-Sto´s et al, 2001;Jakobsen & Tang, 2002;Tang, 2003;Lu¨rling, 2003a, b;van Holthoon et al, 2003;Wiltshire et al, 2003), is a defense mechanism that exists widely in aquatic system. Although M. aeruginosa used in the experiment is toxic, it appears to have no toxic effect on the flagellates.…”

Factors controlling the colonial structure of Pediastrum tetras (Chlorophyceae)

“…In the scientific literature, results of Daphnia grazing or info-chemical effects on algae were obtained for a wide range of time periods, for example, four hours (Wiltshire et al, 2003) or two days (Lürling et al, 1997;Lürling & Van Donk, 1999). We stopped the experiments after five days of grazing activity, by adding several drops of Lugol's solution into the flasks.…”

“…For example, variations occur in the trichomes of Limnothrix redekei (Van Goor) Meffert (Meffert & Oberhauser, 1982) or in colony formation of Pediastrum (Davis, 1967;Millington & Rasch, 1980). Moreover, morphological changes are driven by abiotic factors such as temperature (Lürling & Van Donk, 1999), nutrients (Verity & Medlin, 2003), pH (Neustupa & Hodac, 2005), and relative water column stability (Naselli-Flores & Barone, 2003) or by biotic factors such as grazing (Wiltshire et al, 2003), grazer info-chemicals (Tang, 2003), competition (Yoshida et al, 2004), or allelopathy (Mulderij et al, 2005) and even by the combined effect of abiotic and biotic factors (Lürling & Van Donk, 1999).…”

“…Moreover, the defense reactions of algae to predators may also produce morphological changes. These mechanisms have been widely studied only in the Scenedesmus-Daphnia system (Hessen & Van Donk, 1993;Lürling & Van Donk, 1999) and have been unclear in other algal groups (Wiltshire et al, 2003). Therefore, studies involving an isolated population of colony-forming alga are useful for highlighting the possibilities of algal morphological expression and for obtaining inferences about the ecology of similar algae.…”

Morphological variation in Staurastrum rotula (Zygnemaphyceae, Desmidiales) in the deepest natural Brazilian lake: essence or accident?

“…Morphological and physiological modifications of planktonic algae are nothing but adaptation mechanisms for its life in suspension (Reynolds, 1984), protection against herbivory (Wiltshire et al, 2003) or response to environment contrasts (Morales et al, 2002). Desmid's morphological complexity is induced by evolution processes (Kouwets, 2008).…”