Environmental stress and infectious disease in aquatic ecosystems (GEDIHAP)

Aquatic ecosystems like rivers, lakes and coastal areas are subject to a multitude of anthropogenic stress factors. These include climate change, eutrophication and oligotrophication, pollution and species introductions. These stress factors modify dynamics of individual populations and whole communities, and in some cases populations may be driven to extinction resulting in a loss of biodiversity.

In this CCES project we bring together approaches from two different fields, ecotoxicology and evolutionary biology with the aim to comprehend interactions between environmental stress and disease. The project addresses questions raised from the conceptual model on the interactions between environmental stress, disease and genetic diversity as presented in Figure 1.

Figure 1 Disease in parameter space. The line dividing the parameter space represents Ro = 1 (no intrinsic rate of increase for an infectious disease entering an uninfected host population). The disease can only invade regions of parameter space to the right where Ro > 1. Increases in susceptibility increase Ro as do increases in host carrying capacity. Increased parasite death rates decrease Ro, making it more difficult for a disease to invade. Dashed arrows indicate hypothetical effects of stress on where populations reside in parameter space. Filled circles represent diseased populations and open circles represent populations without disease. Stress can expose an uninfected population to disease or it can lead to the extirpation of a disease [Lafferty, Holt, Ecology Let, 2003, 6, 654].

For instance we are testing the hypothesis if infection with parasite Caullerya mesnili of Daphnia galeata is different for clones hatched from different sediment layers and hence different years and later on how water pollution influences this interaction. In another experiment we study the effect of two stress factors on hosts from sediment layers with different parasite density. For this Daphnia magna is exposed to the parasite Pasteuria ramosa and the insecticide Diazinon.

We are also investigating host parasite association between Asterionella formosa and Zygorhizidum planktonicum in combination with the herbicide Diuron as chemical stressor. We developed and tested 10 microsatellite markers for the host, which will allow us to study levels of genetic variation in the host. We also monitored (in a preliminary way) this year’s spring bloom in the eutrophic Greifensee and the mesotrophic Lake Zürich for chytrid fungal infection, which was successful. The presence of both host and parasite in both lakes, which differ in trophic state, creates possibilities to conduct comparing field studies of chytrid infection dynamics. In addition, the availability of the microsatellite markers offers the opportunity to analyze the extend of genetic diversity within and between A. formosa populations from different geographically distributed lakes.