Comparing phenotypic plasticity in bacterial prey traits and ecological consequences by using specialist vs. generalist strains and organic aggregates as model systems

• Applicant: Professor Dr. Hans-Peter Grossart
• Subject Area: Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions ; Microbial Ecology and Applied Microbiology
• Term: from 2014 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257346203

Changes in bacterial cell size, microcolony formation and attachment to particle/aggregate surfaces can be regarded as key traits of aquatic bacteria to counteract protozoan grazing and changes in environmental conditions, e.g. the availability of nutrients and organic matter. Thereby, specialist with a low phenotypic plasticity (non-plastic, either free or surface attached) can be distinguished from generalists with a high phenotypic plasticity (plastic, switching between free and surface-attached life stages). Trait plasticity can be induced (phenotypic plasticity; generalists) or inherited (rapid evolution; specialists). Theoretically changes of specialists with a low phenotypic plasticity (either free or attached) lead to pronounced predator-prey cycles, whereas generalists with a high phenotypic plasticity dampens these oscillations and hence stabilize the system. Models predict that generalists are favored by fluctuations in environmental parameters, e.g. ecosystem disturbances, but that their stabilizing effect leads to a preference of specialists. Yet, such differences in bacterial lifestyle have not been taken into account when experimentally analyzing predator-prey interactions and dynamics. Our proposal addresses the core question of DynaTrait, i.e. by which mechanisms the existing trait variation at the prey/predator levels influences the dynamics at both trophic levels, which then feeds back on the maintenance of trait variation. We will combine experimental and modelling enterprises to examine the (combined) effects of rapid evolution and phenotypic plasticity of antipredatory defense on predator-prey dynamics in chemostats. Instead of using only one predator with high phenotypic plasticity, we will use 2 predators with a narrow plasticity (a predator grazing free bacteria and a second predator feeding on surface-attached bacteria).Our work focus on the different bacterial lifestyles and hence physiological traits of specialist and generalist prey bacteria. We propose that generalist prey dampens predator prey cycles and thus stabilize the system. Stable environmental conditions should lead to dominance of non-plastic specialist prey (small trait range), whereas changing environments should favor plastic generalist prey (high trait range). Phenotypically plastic prey thus determines coexistence of 2 different specialist predators and changes in specialist to generalist bacteria ratio affect organic matter cycling efficiency and ecosystem functioning. The tight inter-linkage of chemostat experiments and modeling enterprises allows us to elucidating ecological and evolutionary patterns for generalization of interactions between microorganisms. In a second step we aim to link these patterns to organic matter cycling in the system. Thus we will use the trait based approach to better define to which extent phenotypic plasticity on the microorganism level feeds back to biodiversity and ecosystem function.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1704: Flexibility Matters: Interplay Between Trait Diversity and Ecological Dynamics Using Aquatic Communities as Model Systems (DynaTrait)
• Participating Persons: Professorin Dr. Ursula Gaedke; Professor Dr. Guntram Weithoff