I combine experimental, theoretical, meta-analytical, and genomic approaches to investigate how natural ecological and genetic variation shape microevolution. I’m currently investigating adaptation and constraint in the plant microbiome.
Evolutionary genetics of the plant microbiome
In wild populations, organisms simultaneously interact with mutualists and antagonists, raising two fundamental questions: How do hosts attract mutualists while repelling antagonists?; and How does adaptation proceed in the face of this conflict?
I am investigating these questions using two microorganisms that impact plant fitness in wild populations and crop yields in agricultural systems: mutualistic rhizobia and parasitic nematodes. Rhizobia benefit the plant by providing it with nitrogen, while nematodes harm the plant by stealing photosynthates. Even though one is a mutualist and the other an antagonist, these symbioses are strikingly similar. Both reside in specialized symbiotic root organs (right), and many of the same genes are involved in both symbioses.
To determine whether hosts respond independently to mutualists and antagonists, I am combining quantitative genetics and transcriptomics to test whether plant responses to rhizobia and nematodes are genetically correlated, and to dissect how nematodes and rhizobia shape genetic variation in plant traits.
Environmental effects on evolutionary constraint
For decades, geneticists have recognized that the environment impacts genetic constraints, but the evolutionary significance of these effects is hotly debated. I have shown that environmental effects on genetic constraint are strong, and interact with changes in selection to significantly alter the rate of evolution.
In a meta-analysis of genetic variance-covariance (G) matrices, I showed that environmental effects on genetic correlations are extensive and evolutionarily significant (Wood and Brodie 2015 Evolution), rivaling the changes that accumulate due to the combined action of selection, migration, mutation, and genetic drift. Using a theoretical model, I showed that environmental effects on genetic variation considerably alter evolutionary rates when correlated with changes in selection (Wood and Brodie 2016 Ecology Letters), a previously almost entirely overlooked phenomenon. Together, 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.
The evolution of local adaptation
The circumstances under which local adaptation evolves inform the relative importance of adaptation and constraint in natural systems. Through experiments in wild and laboratory populations in plant and animal systems, I have shown that local adaptation frequently fails to evolve.
Plants — Theory predicts that local adaptation may be weaker in mutualisms than in antagonisms. I collaborated with Tia Harrison (Stinchcombe lab MSc student) to test this hypothesis in the model mutualism between legumes and nitrogen-fixing rhizobia, and found no evidence for local adaptation in the legume Medicago lupulina despite a large-scale cline in its rhizobial assemblages (Harrison, Wood et al. in review). In addition to this experimental work, I am collaborating with John Stinchcombe and Stephen Wright (University of Toronto) to compare the relative roles of population-specific selection—which drives local adaptation—and rangewide selection in shaping genetic variation on long timescales in the plant Capsella grandiflora.
Insects — Host-associated insects are excellent systems for investigating adaptation to different environments (host species) without sacrificing ecological complexity. In a series of field and laboratory experiments at Mountain Lake Biological Station, I tested for local adaptation in the forked fungus beetle (Bolitotherus cornutus) to its three host fungus species (above). Although I demonstrated that the three fungi differ dramatically in their quality as developmental environments (Wood et al. 2014 Behavioral Ecology), local adaptation has not evolved in this system. Populations on the three host fungi are not genetically differentiated (Wood et al. 2013 Ecology and Evolution), and wild females do not preferentially oviposit on the high-quality host (Wood et al. in prep).