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We study the ecology and evolution of species interactions in the plant root microbiome.

Evolutionary ecology of host-associated communities

Macroorganisms interact with a diverse array of symbionts, both beneficial (mutualists) and harmful (parasites and pathogens). Our lab studies how the interactions between hosts and symbionts shape their genomes, phenotypes, and ecological communities. We're especially interested in the causes and consequences of conflicts that arise as organisms navigate interactions with multiple partners.

We explore these questions in the plant genus Medicago and its community of root-associated microorganisms, through a combination of field surveys, greenhouse & field experimentsstatistical genetics, and genomics

Medicago and its symbionts

Medicago is a genus of plants in the bean family (Fabaceae). It includes a genetic model species for host-symbiont interactions (M. truncatula); a wild weed naturalized in North America (M. lupulina); and the forage crop alfalfa (M. sativa). 


We focus on Medicago's interactions with two major endosymbionts: mutualistic rhizobia bacteria that fix nitrogen for the plant in exchange for sugars, and parasitic root-knot nematodes that form galls on plant roots and steal nutrients.

Medicago botanical illustrations.png

Current projects

Genetic correlations in multispecies interactions

Pleiotropy (when one gene affects multiple traits) creates genetic correlations between traits. Genetic correlations affect evolution because evolution in one trait affects correlated traits via their shared genetic basis. Genetic correlations in morphological, behavioral, physiological, and life history traits have been studied for nearly a century, but genetic correlations in species interactions have been largely overlooked (Rebolleda-Gómez and Wood 2019).


Research in our lab focuses on genetic correlations linking host responses to multiple symbionts. We discovered that there is a genetic tradeoff between recruiting rhizobia and resistance to nematodes in Medicago (Wood et al. 2018): plant genotypes that formed more nodules were more heavily infected by nematodes. Current work in the lab is investigating the causes and consequences of this genetic correlation between recruiting mutualists and resisting parasites.

Current research questions

  • What underlying mechanism causes the tradeoff between mutualism and parasitism?

  • Do symbiosis-specific and pleiotropic genes exhibit different evolutionary dynamics?

  • Are genetic correlations in species interactions evolutionarily conserved? ​

Ecology & evolution of interacting phenotypes

Interactions between individuals influence the expression of many traits. These traits—known as interacting phenotypes, extended phenotypes, or joint traits—are unique in that they are shaped by the genomes of multiple species. We're interested in how interactions between species influence trait expression and genetic architecture (genetic variances and correlations with other traits), and in the evolutionary dynamics of these traits.


Our past work suggests that these context-dependent effects are evolutionarily significant. We discovered that context-dependent changes in genetic architecture are large (Wood and Brodie 2015), and that when they co-occur with changes in selection, they can accelerate or constrain trait evolution (Wood and Brodie 2016). 

Current research questions

  • When and how do parasites impact cooperation in host-microbe mutualisms?

  • What host traits are most strongly affected by interactions with microorganisms?

  • Which interactions /contexts have the largest effect on trait expression, and why?

Assembly & function of host-associated communities

Plants and animals host thousands of microorganisms. A major open question is whether and how ecological processes in these host-associated communities differ from the communities of free-living organisms that have been the historical focus of community ecology.


Several ongoing projects in our lab are exploring the assembly, structure, and function of host-associated communities. We recently showed that priority effects between co-colonizing rhizobia and nematodes impact colonization outcomes (Burr et al. in press), and that parasitic nematodes impact plant-plant competition (Catella et al. in press).

Current research questions

  • Do correlated host responses to multiple microbes shape the assembly of host-associated communities?

  • How does host development modify host-symbiont interactions?

  • How do interactions with other species (e.g., soil microbes, herbivores) affect the recruitment, costs, and benefits of key symbionts? 



Field stations

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



Current projects
Field stations
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