Dynasym

This project aims to investigate the ecological dynamics of freshwater endosymbiosis. We expect that the costs and benefits of endosymbiosis and the contribution of autotrophic and heterotrophic nutrition depend on both population density and the species-specific trait "motility". To investigate such relationships, a rigorous experimental approach using different motile model species that host endosymbionts is required. Within our project, we will follow the population dynamics of a motile Paramecium species, a motile/sessile Stentor species and a sessile Hydra species along population density gradients and different resource supplies. We will address the following project specific objectives:

-Investigate different density-dependent dynamics of autotrophic and heterotrophic feeding pathways in sessile and mobile endosymbiont-hosting species.

-To analyse the population dynamics of endosymbiont-hosting species and purely heterotrophic counterparts along density gradients under simplified laboratory conditions and in more complex systems.

-To analyse the population dynamics of the endosymbiont in all investigated species along density gradients under simplified laboratory conditions and in more complex systems.

Our proposed work programme will investigate the contribution of photosynthetic versus heterotrophic nutrition of species hosting endosymbionts (PAM analyses + stable isotope analyses). The population dynamics of the endosymbiont itself will be estimated by microscopic cell counting and fast fluorescence kinetic measurements directly in the host. Thus, we will be able to determine the direction of heterotrophic and autotrophic contribution to the total carbon budget, which will allow us to test our theoretical assumptions that the motility trait influences the resource use efficiency of the resources required for autotrophic and heterotrophic nutrition in different strengths/directions. We will further add competitive interactions by increasing the complexity of the experimental systems and introducing closely related heterotrophic and autotrophic species into our systems. We will then track the direction and strength of host and endosymbiont density dependent responses within the more complex experimental setup. Our model systems will allow us to test the central hypotheses of DynaSym and thus directly contribute to its main goal, namely, to gain a process-based understanding of density-dependent symbiosis and to develop an integrative concept of the impact of symbiosis on population and community dynamics.