Marine Ökologie

Host Parasite Coevolution


How specific is innate immunity? - Assessing genome wide gene expression under controlled parasite challenge in three-spined stickleback


DFG-project within programme Host-Parasite Coevolution; PI Thorsten Reusch; doctoral students David Haase, Jennifer Rieger


This project focuses on the effects of parasite genetic diversity on the immune response of the three-spined stickleback (Gasterosteus aculeatus). As model parasite we use Diplostomum pseudospathaceum, a digenean trematode with a complex life cycle. This parasite targets the great pond snail (Lymnea stagnalis) and different species of fish as intermediate hosts and piscivorous birds as definitive hosts. In its 2nd larval phase, the parasite’s metacercariae migrate to the fish’s eye lens, inducing severe fitness costs. While infecting the fish host, the parasite is attacked by both the innate and the adaptive immune system. Adaptive MHC-based immunity is a highly specific system to counteract parasite attacks but its initiation is rather slow. Hence, most parasite attacks are cleared by the phylogenetically older innate immune defence, which may be more specific than previously thought. In order to explore the specificity of the innate immune response in sticklebacks, we established selection lines of resistant and susceptible fish families. These were infected with distinct parasite genotypes, which were isolated and amplified by channelling them through snail and fish hosts, using European Herring Gulls (Larus argentatus) as definitive hosts. We then used single and multiclonal infections of D. pseudospathacaeum and investigated RNA expression patterns using next generation sequencing approaches on the Illumina platform. In a second experiment we focused on the gene expression of repeatedly infected sticklebacks to investigate differences in expression pathways under homologous and heterologous infection treatments.




Interactive effects of environmental change and host-parasite co-evolution on the ecological speciation of sticklebacks


Project funded by the Lead Agency program. PI Christophe Eizaguirre.

How human-caused environmental change affects the ecological and evolutionary processes that create and maintain biodiversity is a pressing question in biology. The eutrophication of aquatic ecosystems is a widespread and ongoing problem that has manifold consequences for sustaining critical ecosystem services, including water quality and biodiversity. The loading of nutrients (e.g. phosphorus and nitrogen) to freshwater environments not only affects their chemical and physical condition, but also influences the nature of interactions between species such as host-parasite interactions which generate local adaptation patterns and may even lead to speciation. Pervasive effects of eutrophication can alter selection regimes and therefore, cause unexpected evolutionary changes in populations over short time scales. Here, using three-spined stickleback as a model system, we focus on how the interactive effects of nutrient loading and parasites might drive rapid evolutionary changes and breakdown of local adaptation. First, using an intensive field survey along a lake productivity gradient, we will test how lake productivity co-varies with i) parasite diversity and community composition, ii) host genotype diversity, and iii) host immune system function and gene expression- testing for local adaptation of host and parasite populations. Second, using a large scale experiment in mesocosms (42 X 1000 L), we will test how contrasting natural selection regimes, resulting from orthogonal combinations of parasites and nutrient levels, can affect phenotypically and genotypically stickleback adaptive abilities. In this experiment, we focus on phenotypic and genetic traits that have been implicated in mate selection, so that we can test if the contrasting selection regimes caused by manipulating nutrients and parasites (antagonistically) synergistically might contribute to population divergence, and play a role in (reverse) speciation. This work will shed light on how natural and sexual selection are mediated by parasites and environmental conditions, and how these processes jointly respond to divergent environments and affect the progress towards speciation.



Emerging marine disease: why to shift from friendly to nasty?


Project funded by Future Ocean Excellence Cluster

 PI: Olivia Roth, Hinrich Schulenburg (CAU Kiel), Carolin Wendling & David Haase


Pathogens exert extreme selective pressure on their hosts and are highly
prevalent in the marine realm and thus of central importance for marine ecosystem dynamics. Yet, to date, we still lack precise understanding on the complexity of environmental changes that determine shifts in pathogen virulence and thus influence the dynamics of host-pathogen interactions in the oceans. We here aim at developing a “virulence-atlas” for the most abundant marine pathogens from the genus Vibrio. We will take a multidisciplinary approach by integrating several virulence parameters in over 200 isolated Vibrio strains, infection experiments in two established host systems, and candidate virulence gene analysis, in each case under alternative environmental conditions. This project will yield a comprehensive baseline data set essential for an in-depth understanding of the consequences of emerging marine diseases under future scenarios of global change.



Trans-generational immune priming & sexual immune dimorphism across a parental care gradient in two fish families


Project funded by the DFG

PI: Olivia Roth

Males and females have different life-history strategies due to the anisogamy of their reproductive elements. In conventional sex role species, female fitness is positively correlated with longevity, whereas males are selected for increasing mating rates. This is also reflected in the sexual immune dimorphism suggesting that females usually need a greater immune defence than females to efficiently fight parasites and pathogens. In addition, only females transfer immunity to their offspring due to both mechanistic and evolutionary constraints.

In species with increased paternal care, these principles may fall. With higher paternal investment into offspring we hypothesize sexual immune dimorphism to be inverted: if paternal investment is higher, males should have a greater immune defence than females as now they are the limiting sex. In addition, if offspring are born in paternal environment, fathers should be selected to boost the offspring immune system as they will be exposed to similar parasite pressures.

We want to investigate these evolutionary concepts in two fish families with a parental investment gradient, Syngnathids and Cichlids. This project will enhance our understanding of selection pressures of immune defence evolution and determine the effect of parental care on immune defence dyamics and parasite defence.



Manipulation of bacteria-fish interactions through marine viruses – an evolutionary Analysis


Project funded by the Volkswagen Foundation

PI: Olivia Roth

Evolution and maintenance of mutualism are difficult to explain by means of natural selection, as cheaters are likely to outcompete cooperative individuals. Accordingly, the shift from mutualism to parasitism is commonplace in nature, and can be induced by a third player that intervenes in the interaction between a symbiont and its host. Temperate phages are a typical example. They integrate into the genome of mutualistic bacteria and convert them into parasitic diseases - Cholera being one of them. Such tri-partite interactions quickly generate chaotic oscillations and their evolutionary dynamics are therefore difficult to predict.

Consequently, despite their importance, these interactions are rarely studied. I propose to use a model system consisting of the pipefish Syngnathus typhle, bacteria of the genus Vibrio, and their temperate phages to study tri-partite interactions experimentally. My experiments will focus on the processes that lead to local adaptation and generate a geographic mosaic, on the applicability of the matching alleles hypothesis, and on virulence evolution. All these concepts have been developed in the framework of hosts and constitutive parasites and their validity in more complex communities is not known. Data that are obtained empirically are then integrated into a mathematical model. I expect that modification and manipulation of the system by the third player, the phage, has profound effects on host-parasite interactions and will challenge long-standing conventional concepts of antagonistic co-evolution.