Speaker
Description
From phytoplankton producing the planet’s oxygen to wildebeest grazing the Serengeti, each species modifies their ecosystem. These ecological changes can precipitate adaptive evolution, which in turn can lead to further changes in the ecosystem. Previous studies have shown that this coupling between ecological and evolutionary processes is often driven by interactions between species. While there are a number of case-studies of individual demonstrations of eco-evolutionary feedbacks and the role of species interactions in driving these feedbacks, the details of how they work are not well understood. In particular, we do not know how the addition of a species to a community impacts the distribution of adaptations available to other community members, and how these adaptations in turn affect community ecology. We address this gap in an experimental microbial community consisting of the yeast Saccharomyces cerevisiae and the alga Chlamydomonas reinhardtii, which have been previously shown to form an obligatory mutualism in certain laboratory conditions (Hom & Murray, Science 2014). We modified these conditions to make this mutualism facultative, which allowed us to measure (1) how addition or removal of one community member (algae) changes the adaptive mutations available to another member (yeast) and (2) how these mutations in turn alter the ecology of the community. We sampled hundreds of adaptive mutations in each condition to gain a quantitative understanding of how a species interaction affects community eco-evolution. We show that yeast adaptation is highly diverse at both the genetic level and in their effect on community ecology, as some adaptations decrease the yield of one or both species while others increase one or both yields. However, algae algae systematically alter the distribution of community impacts by favoring adaptations that increase the yield of both species. This bias can be explained by understanding the dynamics of rapid adaptation in large asexual populations. As a result of this bias, evolution becomes more repeatable at the community level compared to the evolution of yeast in isolation.
