Molecular and physiological mechanisms of fungal parasitism and their ecological consequences in polar waters

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Benthic diatoms play an ecologically important role as primary producers for polar aquatic ecosystems as they provide food for higher trophic levels including fish. Yet, little is known how their biomass production is affected by parasites, e.g. basal fungi called chytrids. In a previous project, we detected the frequent occurrence and a high diversity of chytrids in both Antarctica and the Arctic. Yet, we were not able to mechanistically study their ecological role for food web dynamics and C-cycling, in particular under global climate change scenarios. Thus, in accordance with SPP 1158 Antarctic Research, our project addresses the two major overarching questions: I. Gateways to Lower Latitudes and II. Response to Environmental Change. Field work will be performed with other SPP members at Potter Cove (Dallmann Lab, Carlini Station, Antarctica) and Kongsfjorden (AWIPEW Station, Ny-Ålesund, Svalbard). Our main questions are: How do host-parasite (benthic alga-chytrids) dynamics and physiology change under different environmental conditions, how will environmental change affect the ecological role of chytrid parasites, and how do they survive periods of complete darkness in a warming ocean? Four goals will be addressed: i) Evaluate and compare host-parasite dynamics under different environmental conditions in Potter Cove (Antarctica) vs. Kongsfjorden (Arctic) via field and experimental studies (incl. microscopic and molecular tools). ii) At both study sites, examine and compare changes in host-parasite physiology under changing environmental conditions using field and experimental studies (incl. metabolomics). iii) Determine the ecological role of host-parasite interactions under changing environmental conditions and compare both Antarctic vs. Arctic study sites. iv) Define parasite strategies to survive periods of continuous darkness in a warming ocean and describe the host-parasite system on the cellular level via metabolomics combined with lab and field incubations. We will test the following hypotheses: H1: Host-parasite (benthic alga-chytrid) “diversity” changes as a response to a changing environment (i.e. temperature and light availability). H2: Predicted environmental changes will affect host-parasite “interactions” with implications for their ecological role in polar coastal waters, which may lead to differences in benthic food webs and C-cycling at Antarctic vs. Arctic sites. H3: During periods of complete darkness and low temperatures (1°C; polar winter), parasites form special resting stages and/or switch to generalist strategies. Our study will provide a mechanistical insight into climate-change related impacts on the ecological role of benthic diatom-chytrid interactions and their consequences for food web dynamics and hence C-cycling. The combination of single cell metabolomics and metatranscriptomics enables to explore metabolic consequences of largely neglected benthic protist-parasites interactions in polar regions.