I integrate field and laboratory approaches to study how genetic variation has been shaped by past selection, and how it will shape future adaptation. My ongoing research explores these questions through the lens of genetic conflict in the plant microbiome.
Genetic conflict in the plant microbiome
Nearly all species require mutualists to perform vital functions. However, many mutualism genes are also used in defense, raising the intriguing possibility that susceptibility to infection is a pleiotropic cost of mutualism. My goal is to resolve a fundamental paradox posed by the shared genetic control of beneficial & harmful symbioses: how do organisms attract mutualists while repelling parasites, and what are the ecological and evolutionary consequences of this conflict?
In collaboration with my postdoc advisor, John Stinchcombe, I developed a novel system to address these questions: I identified an ecologically relevant parasite that disrupts the mutualism between legumes and nitrogen-fixing bacteria (rhizobia). Legumes rely on nitrogen provided by rhizobia to grow in poor soil, but they are also infected by parasitic root-knot nematodes that steal nutrients. Rhizobia and nematodes form strikingly similar structures on plant roots (left), and the same plant genes mediate both interactions.
My ongoing research explores the genomic basis, ecological mediators, and evolutionary consequences of genetic conflict between the rhizobia mutualism and nematode parasitism in clovers in the genus Medicago.
The evolution of local adaptation
Local adaptation evolves because selection favors different optima in different environments. I study constraints on adaptation to understand why some organisms are poorly suited to their environment, and, ultimately, to infer when populations may fail to adapt to ecological change.
Constraints in natural landscapes prevent habitat choice. In collaboration with undergraduates in the REU program at Mountain Lake Biological Station, I used a genetic capture-recapture approach to reconstruct oviposition site choice, a classic signature of local adaptation, in wild female beetles (Bolitotherus cornutus). We found that although females avoided a high-mortality habitat in laboratory trials, this adaptive preference disappeared in the wild (Wood et al. accepted, The American Naturalist). 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 explained why these beetles are not locally adapted (Wood et al. 2013 Ecology and Evolution, Wood et al. 2014 Behavioral Ecology).
Environmental effects on evolutionary potential
Genetic variation, the raw material of evolutionary change, 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. Using meta-analytical and theoretical approaches, I 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. In a meta-analysis, I found that differences in genetic correlations among environments were as large as evolved differences among populations (Wood & Brodie 2015 Evolution), demonstrating that environmental effects on genetic correlations rival other evolutionary forces (selection, migration, mutation, and genetic drift) (Wood and Brodie 2015 Evolution).
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 a simple analytical model, I showed that concurrent changes in evolutionary potential and selection alter evolutionary rates (Wood and Brodie 2016 Ecology Letters, recommended by Faculty of 1000). My research suggests that environmental effects on genetic constraint may play an outsize role in shaping evolutionary trajectories in an era of rapid environmental change.