My research is broadly motivated by the desire to understand how abiotic and biotic factors shape organismal evolution and phenotypic expression. I use two model genetic systems to explore ecological and evolutionary questions:

  1. A rhizobium/legume system where the genes underlying the resource mutualism between these two organisms have been extensively studied
  2. Arabidopsis thaliana a genetic model organism where the gene networks underlying life-cycle transitions have been intensively studied

Evolutionary ecology of the rhizobia/legume mutualism


When living in symbiosis with legume hosts, rhizobial bacteria convert atmospheric nitrogen into a plant-available form. In exchange, rhizobia receive carbon in the form of dicarboxylates and a favorable environment for reproduction. Rhizobia do not always live in symbiosis and the majority of the population at any given time are free-living microbes in the soil. Little is known about how adaptation to the free-living environment affects the stability of the mutualism or the extent to which host genotype mediates competitive outcomes between closely related microbial strains.


  • Novel Select and re-sequence methodology to:
    • Measure rhizobial fitness in symbiotic and free-living environments and identify the genomic basis of fitness in microbes (CV and Publications)
    • Test evolutionary consequences of host/free-living cycles
    • Screen for strain specificity in the plant-microbe interaction
  • The transcriptomic basis of host genome by symbiont genome interactions in Medicago truncatula nodules (CV and Publications)
  • GWAS to determine the genetic architecture of and identify natural genetic variation in stress and metabolic tolerance traits in rhizobia (with Brendan Epstein, submitted)

Life cycle phenology of Arabidopsis thaliana: environmental and genetic contributions across landscapes

In annual plants, the timing of germination, flowering, and seed dispersal define the life cycle and the timing of these developmental transitions (phenology) exhibits plasticity in response to altered climatic conditions, whether caused by climate change or by dispersal into new locations. The timing of these transitions are critical because for these sessile organisms they define the seasonal conditions that each life stage must survive through. What factors shape when organisms transition from life stage to life stage? How do these transitions function together across the range of a species to determine life cycles?  How will climate change and long-distance/human-mediated dispersal influence life cycles? And ultimately, how does changing life-cycle expression change fitness? Further, as the word life cycle itself emphasizes, life cycles are inherently cyclical and yet they are often studied linearly in ways that de-emphasize connections between generations. How important are these trans-generational connections for life-cycle expression?


  • Predicting Arabidopsis thaliana life-cycles across landscapes (CV and Publications)
  • Life cycle consequences of  temperature-dependent dormancy induction during seed maturation (CV and Publications)
  • Influence of fluctuating temperatures on flowering time (CV and Publications)
  • Environment dependent survival models to quantify chronic and acute stressors (with Bradley Tomasek and Bob Shriver submitted)
  • The natural history of local A. thaliana populations (with Lindsay Leverett)
  • Building models of germination timing that include secondary dormancy dynamics and maternal effects (with K. Donohue)

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