Department of Biological Science

Mutualistic interactions between species are vital to life. Organisms across all domains of life depend on other species for an array of important functions, including supplementing nutrition, providing defense against pathogens, and increasing tolerance to environmental stressors. Our lab investigates the coevolutionary dynamics that underpin long-term mutualistic interactions using a multi-faceted approach. We evaluate the factors contributing to mutualism stability in natural populations of insects and their bacterial symbionts. We complement this work with experimental evolution in a synthetic system of mutualistic cross-feeding using Saccharomyces cerevisiae. We use an array of approaches, including genomics, field-based analysis, cross-infection studies, experimental evolution, and molecular genetics to elucidate the eco-evolutionary dynamics underlying mutualism.

Current Research Areas:

Evolution of environmentally acquired symbioses

Many hosts acquire their microbial symbionts from the environment each generation. This transmission pathway presents challenges for both hosts and symbionts. Symbionts experience selection in both the external and host environment. This may result in tradeoffs for symbionts if adaptations for one environment are costly in another. Hosts must identify and select beneficial symbionts from a diverse pool of potential partners that can vary in quality. The uncoupling of host and symbiont life cycles increases opportunities for hosts to acquire exploitative symbionts. Using the interactions between the squash bug Anasa tristis and its bacterial Caballeronia symbionts, our lab aims to identify the evolutionary processes underpinning the maintenance of cooperation in environmentally acquired host-microbe symbioses. We are doing this by evaluating how the differential selection pressures experienced by symbionts affect population structure, whether symbionts experience tradeoffs due to differential selection pressures, and the consequences of the symbiont adaptation to external selective conditions for host fitness. We are exploring these ideas using genomics and cross-infection studies.

Host-symbiont communities and diffuse coevolution

Much of our understanding of coevolution between hosts and symbionts comes from empirical work and theory evaluating how pairs of species reciprocally evolve in response to one another. However, these pairwise trajectories are likely altered by the range of interactions experienced within species-rich communities. Increasingly, empirical evidence from mutualisms in nature suggest these community-level interactions play an important role. Using field collections and genomics, we are investigating whether community structure and diffuse coevolution contribute to the maintenance of cooperation between Coreid insects and their Caballeronia symbionts.

Partner fidelity and mutualistic rewards

Opportunities for repetitive interactions between specific partner lineages are predicted to contribute to the maintenance of cooperation. When partner lineages interact across generations, they can impose strong reciprocal selection on one another for the maintenance of beneficial traits in the inhibition of exploitative traits. However, many mutualistic interactions are characterized by promiscuity, such that partner switching frequently occurs, and the fidelity of interaction between specific partner lineages is weak. How cooperation persists and increased rewards evolve in mutualisms with weak partner fidelity is poorly understood. We are currently using experimental evolution of mutualistic S. cerevisiae yeast strains to assess the consequences of temporally varying partner fidelity.