The outcome of a parasite infection may vary greatly depending on the phenotype of the hosts and of the parasite, leading to host resistance, tolerance or to infection and ultimately death. Evolutionary theory attributes this diversity in the outcome of parasite infection to co-evolutionary arms race through time. Briefly, parasites are constantly selected to counteract or disrupt the host defense systems, and hosts are constantly selected to counteract or disrupt new parasite virulence strategies. Recently, this two-partners co-evolutionary dynamic theory has been challenged by the understanding that all eukaryotes are associated with microbes that play key roles in all aspects of their physiology. The holobiont concept captures this community of interacting organisms including the host and its diverse array of symbionts such as bacteria, archae, fungi, algae and viruses. The multi-dimensional linkages between hosts, parasites and their associated microbes produces a complex networks of interactions that will influence the evolution of all the partners. At any given time, the phenotypic outcomes of infection is the direct product of natural selection acting on the host genome, the parasite genome and the genomes of their associated microbes. The research projects in Dheilly’s lab aim at understanding how these associated microbes participate in the ecology and evolution of hosts and parasites.
Development of a model system to investigate the role of microbes in parasite virulence strategies
It is now evident that the microbiome plays key roles in individual’s health and susceptibility to diseases. Parasites spanning all major phyla, including helminthes, viruses, bacteria and fungi have been documented to disrupt their host microbiome. But it is unknown if the modifications in the composition of the host microbiome are beneficial for the parasite, a defense mechanism of the host, or by-products of the pathology. In other cases, parasites carry their own microbes and transmission to the host worsens the patient’s condition. But, what is the significance of the phenomenon for the parasites themselves? The long term goal of this project is to characterize the role of parasite-associated microbes and host-associated microbes in parasite virulence strategies.
We have identified a uniquely tractable vertebrate model system for experimental and field experiments. The tapeworm Schistocephalus solidus is a common parasite of threespine stickleback fish, Gasterosteus aculeatus. We are currently characterizing the microbes associated with Threespine sticklebacks, Gasterosteus aculeatus and its cestode parasite Schistocephalus solidus. We are also developing techniques to manipulate the microbiome of the host, and parasite in order to test the role of individual microbes, and microbiome in the symptoms of infection. Finally, in collaboration with Michael Bell (E&E, SBU) and Martin Kalbe (Max Planck Institute in Evolutionary Ecology, Germany), we are testing the role of the host genotype and parasite genotype in the composition of the host and parasite microbiomes.
Parasites Microbiomes Project
Recent advancement in microbiology has revealed that microbes play key roles in all aspects of the biology of animals and plants. Parasites are no exception. Anecdotal evidence of parasites spanning all major phyla, including insects, helminthes, fungi and bacteria have been documented to be associated with microbes. However, in most cases, it is unknown if a given parasite, or genera is associated with microbes. There is now a critical need to characterize the microbiome associated with parasites across all phyla. This collaborative on-going project aims at characterizing new parasite-associated microbes in a broad array of parasitic species . We are using comparative analyses of the microbiome of related parasite species, or of the same parasite in different intermediate and definitive hosts to determine the specificity of the parasite-microbiome interaction.
Environmental stress and the microbiome
The microbiome has a profound role in health, development and overall physiology of any given organism. In the context of global change, it is yet unclear how environmental stress impacts the microbiome of organisms, potentially driving changes in host physiology, in immune system effectiveness, and hence in its overall susceptibility and resistance to parasites. Marine coastal ecosystems in particular have a well known economic value, and are submitted to global and local anthropogentic stressors, resulting in higher water temperature, lower pH and carbonate saturation. Their impact on the fitness of marine organisms threaten fisheries and aquaculture productivity through reduced growth and higher occurrence of parasites. There is thus a critical need to characterize the effect of environmental stressors on the microbiome and overall physiology of key marine species. In collaboration with Hannes Baumann (University of Connecticut) and Janet Nye (SoMAS, SBU), we are testing the effect of temperature and carbon dioxide on the microbiome composition of the Atlantic silverside (Menidia menidia).