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Group 2
<html><font size=6 face=“Arial”>Mycoloop: tasty parasites</font></html>
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Introduction
Trophic interactions between phytoplankton (primary producers) and zooplankton (consumers) govern the flow of energy in marine systems. Planktothrix agardhii is an abundant marine cyanobacteria. This small phytoplankton displays resistance to grazing by zooplankton such as Daphnia galeata because of its filamentous morphology, production of toxins and low nutritional value. However, Planktothrix can be infected and killed by the obligate parasite Rhizophydium megarrhizum, a chytrid fungus. These parasitic fungi, in turn, have a free-living zoosporic stage that is highly nutritional and an important food source for zooplankton. Thus, parasitic Rhizophydium fungi create an important trophic link between cyanobacteria and zooplankton termed the “mycoloop”.
Additionally, when Planktothrix are infected by Rhizophydium, their morphology and nutritional value change and, consequently, they become more edible to Daphnia. (to be continued)
Assignment
Propose and analyse a mathematical model that describes the trophic dynamics among cyanobacteria (primary producer/host), chytrids (parasite/prey) and zooplankton (grazer/predator).
Questions & Suggestions
(1) Under what conditions can cyanobacteria, chytrids and zooplankton coexist?
(2) Under what conditions do cyanobacteria blooms form?
References
R. Agha, M. Saebelfeld, C. Manthey, T. Rohrlack and J. Wolinska. (2016) Chytrid parasitism facilitates trophic transfer between bloom-forming cyanobacteria and zooplankton (Daphnia). Scientific Reports 6:35039 DOI: 10.1038/srep35039.