COS 35-4 - Temperature influences how predation and competition affect prey evolution

Abstract: Background/Questions/Methods

Predation can drive species evolution within food webs, but how this process may change under complex biotic and abiotic stress is unknown. This understanding is a pressing goal of ecology in a rapidly changing world. To tackle this question, we study how prey evolution under selection by multiple predators changes across temperatures in a microbial system. To keep track of changes in genetic frequencies in the prey population over time (evolution), we used the green alga Chlamydomonas reinhardtii wild type (WT) and the vfl1-1 mutant with defective swimming ability. We used fluorescence flow cytometry to distinguish mNeonGreen-tagged WT from untagged vfl1-1 strain, thus allowing us to keep track of changes in strain frequency over time. We also used flow cytometry to measure the cell clump sizes of each C. reinhardtii strain, showing the plastic response of C. reinhardtii towards predation. We manipulated predator presence, identity, and competition among predators, using two protist focal predators with similar body size, Tetrahymena pyriformis and Glaucoma sp., and the larger Paramecium caudatum as the competitor. We also imposed three temperature treatments (19°C, 22°C, and 25°C). Additionally, we used mathematical modeling to put forward testable predictions about the eco-evolutionary dynamics that could be observed in our experiment. We recorded the density of all protists through fluid imaging and used linear mixed models to analyze the data.

Results/Conclusions

Using ordinary differential equations, we predict complex ecological and evolutionary changes in our system across both biotic and abiotic contexts. Our experimental results support these predictions and show that temperature mediates the effects of predation and competition on prey evolution in predictable ways. We found that 1) different predators select for different prey phenotypes, but, surprisingly, plastic defense traits are not always favored in the presence of predators. 2) Selection imposed by predation on prey genotypes changes in the presence and absence of a competitor. 3) Temperature and predation interactively affect prey ecological and evolutionary dynamics. Additionally, temperature affects what predator becomes dominant, which in turn alters the magnitude and direction of selection driving prey evolution. Overall, our study shows that biotic and abiotic factors that are part of and influence natural food webs in a changing climate have complex, interactive, yet predictable effects on prey evolution under predation.