Effects of stochastic resistance and resistance-breaking on host-parasite coevolution

• Applicant: Dr. Eva Lievens
• Subject Area: Organismic Interactions, Chemical Ecology and Microbiomes of Plant Systems
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 541768773

Host-parasite coevolution, which results from reciprocal selection pressures between hosts and parasites, is an important generator of biodiversity and cause of medical and agricultural challenges. As such it is crucial to understand the factors shaping the outcome of host-parasite coevolution. One understudied factor is that for many hosts and parasites, similar changes in resistance or host range can be caused by a variety of underlying mutations. This mutation diversity introduces stochasticity at every coevolutionary step, which may have cascading effects on the subsequent coevolutionary trajectory. For example, different resistance pathways may have different associated fitness costs or epistatic constraints, or impose different selection pressures on the antagonist. Despite the ubiquity and potential importance of mutation diversity, its consequences for host-parasite coevolution have barely been studied. This project aims to fill this gap by testing the effects of initial stochasticity on the trajectory of alga-virus coevolution. Experimental coevolution in this system follows an arms race of escalating algal resistance and viral host range. In previous work, I isolated 22 algae with diverse resistance phenotypes and 113 viruses with diverse resistance-breaking mutations (mutations expanding host range) from the first steps of their coevolutionary arms race. This unique resource allows the isolation and manipulation of each coevolutionary step. Within this project, I will characterize the genetic and phenotypic diversity of resistance and resistance-breaking. I will then use experimental evolution to test whether initial stochasticity in resistance or resistance-breaking constrains the evolution of algae or viruses within the first coevolutionary steps. This work will answer fundamental questions about the nature of resistance and resistance-breaking, the process of adaptation to ameliorate fitness costs, the existence of trade-offs and epistatic constraints, and the repeatability of (co)evolution. The results will also generate specific predictions for the impact of initial stochasticity on subsequent coevolutionary steps, which will be tested in future work.

• DFG Programme: Research Grants