Genetic conflict between attracting mutualists and repelling parasites
Many genes that organisms use to regulate their mutualists are also used to defend against parasites and pathogens. The shared genetic control of beneficial and harmful symbioses raises the intriguing possibility that susceptibility to infection is a pleiotropic cost of mutualism. Our goal is to understand how a genetic tradeoff between attracting mutualists and repelling parasites has shaped the genomic architecture of traits mediating species interactions, and how ongoing conflict influences adaptation.
We combine fieldwork, experiments, and genomics & transcriptomics to explore these questions in the root microbiome of legumes in the genus Medicago. Legumes rely on nitrogen provided by mutualistic bacteria (rhizobia) to grow in poor soil, but they are also infected by parasitic nematodes that steal nutrients. The two symbionts form remarkably similar structures on plant roots (below).
We've discovered that plant responses to mutualistic rhizobia and parasitic nematodes are genetically coupled in the legume Medicago. Plant genotypes that attracted more rhizobia were more heavily infected by nematodes, indicating that susceptibility to parasitic nematodes is a cost of mutualism.
We're exploring the following questions in the legume genus Medicago :
In a genetic model plant (Medicago truncatula) ...
What are the genomic signatures of genetic conflict between mutualism and parasitism?
In a wild weed (Medicago lupulina) ...
How does genetic conflict influence adaptation?
How does ecology mediate genetic conflict?
In alfalfa (Medicago sativa) ...
How can we mitigate conflict between mutualism and parasitism in crop microbiomes?
Constraints on adaptive habitat choice in the wild
With undergraduates at Mountain Lake Biological Station, I used an innovative genetic approach to reconstruct oviposition site choice, a classic signature of local adaptation, in wild forked fungus beetles (Bolitotherus cornutus). We found that although females avoided a high-mortality habitat in laboratory trials, this adaptive preference disappeared in the wild. Our results show that natural landscapes impose tradeoffs that override adaptive preferences to shape habitat use; reveal that these tradeoffs are significantly stronger than suggested by the laboratory-based work that dominates the habitat choice literature; and may explain why these beetles are not locally adapted.
Wood et al. 2014 Behavioral Ecology |
Forked fungus beetles lay eggs on three fungus species.
From left to right: Fomes fomentarius, Ganoderma applanatum, and Ganoderma tsugae.
Environmental effects on evolutionary potential
Genetic variation, the raw material of evolution, determines a trait's capacity to evolve (its "evolutionary potential"). The environment influences evolutionary potential by modifying gene expression, uncovering cryptic genetic variation under certain conditions. We've discovered that environmental effects on evolutionary potential—typically assumed to be minimal—are extensive and evolutionarily significant.
Environmental effects on evolutionary potential are extensive. Evolutionary potential in multivariate trait space is described by genetic correlations, the relationships between traits that influence evolution. We found that differences in genetic correlations among environments were as large as evolved differences among populations, demonstrating that environmental effects on genetic correlations rival the strength of other evolutionary forces.
These effects interact with selection to alter the rate of evolution. Because selection favors different optima in different environments, environmental effects on evolutionary potential are likely to co-occur with changes in selection. In an analytical model, we showed that concurrent changes in evolutionary potential and selection alter evolutionary rates.
Our research has a large field component. We're lucky to work at three amazing field stations: the University of Pittsburgh's Pymatuning Laboratory of Ecology; the University of Virginia's Mountain Lake Biological Station, and the University of Toronto's Koffler Scientific Reserve. Click on the photos below to learn more about these fantastic facilities.
Pymatuning Lab. of Ecology
Mt. Lake Biological Station
Koffler Scientific Reserve