Multiple trade-offs between defense and competitiveness traits in a planktonic predator-prey system

Predator-prey interactions play a central role in community dynamics and depends on the covariation of traits of the interacting organisms. Intraspecific trade-off relationships between defense and competitiveness traits are important for understanding trophic interactions. However, quantifying the relevant traits forming defense-competitiveness trade-offs and how these traits determine prey and predator fitness remain major challenges. Here, we conducted feeding and growth experiments to assess multiple traits related to defense and competitiveness in 6 different strains of the green alga Chlamydomonas reinhardtii exposed to predation by the rotifer Brachionus calyciflorus. We found large differences in defense and competitiveness traits among prey strains and negative relationships between defense and competitiveness traits. Because we compared trait differences among strains whose ancestors previously evolved in controlled environments where selection favored defense or competitiveness, these negative correlations suggest the presence of a trade-off between defense and competitiveness. This trade-off was found for multiple combinations of defense and competitiveness traits. Furthermore, the differences in traits translated into differences in prey and predator fitness, which demonstrated the contribution of intraspecific trade-offs for predicting the outcome of predator-prey interactions.