title: Chytrid parasitism facilitates trophic transfer between bloom-forming cyanobacteria and zooplankton (Daphnia).
abstract: Parasites are rarely included in food web studies, although they can strongly alter trophic interactions. In aquatic ecosystems, poorly grazed cyanobacteria often dominate phytoplankton communities, leading to the decoupling of primary and secondary production. Here, we addressed the interface between predator-prey and host-parasite interactions by conducting a life-table experiment, in which four Daphnia galeata genotypes were maintained on quantitatively comparable diets consisting of healthy cyanobacteria or cyanobacteria infected by a fungal (chytrid) parasite. In four out of five fitness parameters, at least one Daphnia genotype performed better on parasitised cyanobacteria than in the absence of infection. Further treatments consisting of purified chytrid zoospores and heterotrophic bacteria suspensions established the causes of improved fitness. First, Daphnia feed on chytrid zoospores which trophically upgrade cyanobacterial carbon. Second, an increase in heterotrophic bacterial biomass, promoted by cyanobacterial decay, provides an additional food source for Daphnia. In addition, chytrid infection induces fragmentation of cyanobacterial filaments, which could render cyanobacteria more edible. Our results demonstrate that chytrid parasitism can sustain zooplankton under cyanobacterial bloom conditions, and exemplify the potential of parasites to alter interactions between trophic levels.
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany.
authors.forename: Ramsy
authors.initials: R
authors.lastname: Agha
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany.|Department of Biology, Chemistry, Pharmacy, Institute of Biology, Freie Universität, Berlin (FU), Germany.
authors.forename: Manja
authors.initials: M
authors.lastname: Saebelfeld
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany.
authors.forename: Christin
authors.initials: C
authors.lastname: Manthey
authors.affiliation: Norwegian University of Life Sciences (NMBU), Department of Environmental Sciences, Ås, Norway.
authors.forename: Thomas
authors.initials: T
authors.lastname: Rohrlack
authors.affiliation: Leibniz-Institute of Freshwater Ecology and Inland Fisheries (IGB), Berlin, Germany.|Department of Biology, Chemistry, Pharmacy, Institute of Biology, Freie Universität, Berlin (FU), Germany.
authors.forename: Justyna
authors.initials: J
authors.lastname: Wolinska
mesh_terms: D000818:Animals; D001522:Behavior, Animal; D000458:Cyanobacteria / Q000502:physiology; D003621:Daphnia / Q000235:genetics / Q000502:physiology*; D005247:Feeding Behavior; D020387:Food Chain; D005658:Fungi / Q000502:physiology; D005838:Genotype; D006790:Host-Parasite Interactions; D015048:Zooplankton / Q000382:microbiology*