Host-parasite interactions in hybridizing Daphnia, from correlations to experiments

• Applicant: Dr. Justyna Wolinska
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 312929216

Eutrophication is a worldwide environmental problem accelerated by global warming, affecting the stability of aquatic ecosystems and having long-lasting consequences. We propose to investigate if and how eutrophication affects two interacting evolutionary processes: disease spread and interspecific hybridization. We will study the influence of eutrophication on host-parasite interactions in a hybridizing system and on hybridization success per se. We will use waterfleas (Daphnia) as a hybridizing host and the ichthyosporean Caullerya as a pathogen. This Lead Agency Project is a combination of field surveys of two lakes (Müggelsee, DE and Greifensee, CH), a large scale pond experiment (CH), the transcriptional profiling of stress-exposed Daphnia (CH), and the development and application of molecular markers (DE) that will allow us to study parasite evolution in hybridizing Daphnia. Eighteen experimental ponds will be inoculated with 100 Daphnia clones, which will then experience high, moderate or low trophic conditions and presence or absence of parasites. These clones were isolated from the water column of Greifensee or hatched from diapausing eggs preserved in the lake sediment, representing different ages of origin, and different species and hybrids. We will test whether Daphnia that used to live in Greifensee under highly eutrophic conditions (1960s-70s) are better adapted to high nutrient load than clones that experienced cleaner conditions later on. Then, we expect that epidemics will be greater in eutrophic ponds, because of the presence of cyanobacteria which seem to facilitate Caullerya infection. We aim to develop a set of polymorphic molecular markers for the parasite Caullerya, to be able to test if the parasite infects host genotypes in a strain-specific manner and if these associations are further shaped by trophic conditions. These markers will be used in the pond and in the field studies. To gain a mechanistic understanding of the previously observed correlational pattern between parasite epidemics and blooms of cyanobacteria (a by-product of eutrophication), Daphnia will be transcriptionally profiled under parasite and parasite-free conditions while in the presence or absence of cyanobacteria. Finally, using long-term field collections of Daphnia, we will verify if pathogen spread is intensified under the presence of cyanobacteria. The proposed research, a result of close collaboration between Swiss and German scientific teams, will advance our understanding of the environmental forces driving evolutionary processes in natural systems. Overall, through the unique combination of expertise and methods, this project will improve our understanding of disease spread and biodiversity loss under different trophic conditions and, consequently, might provide tools for management of aquatic ecosystems.

• DFG Programme: Research Grants
• International Connection: Switzerland
• Co-Investigator: Privatdozent Dr. Piet Spaak