Research

Our currently funded research projects include:

  1. Studies of the marine ciliate genus Mesodinium as a model system for how acquired metabolism can promote energy generation and stabilize microbial communities (supported through 2021 by the Army Institute for Collaborative Biotechnologies).
  2. Experimental evolution of marine mixotrophs in response to climate change. If mixotrophs become more heterotrophic under warmer ocean temperatures, they could mediate a positive climate feedback loop (supported through 2022 by the National Science Foundation Bridging Ecology & Evolution program).
  3. Understanding the epigenetic mechanisms that modulate coral bioenergetics. We use a combination of empirical and modeling approaches to understand epigenetic-energetic linkages in this model system for acquired metabolism via metabolic mutualism (supported through 2024 by the National Science Foundation Rules of Life program).

While a few general research themes are described below, one of the great privileges of mathematical ecology is that we are often able to work on a wide array of biological questions. Recently, researchers in the lab have worked on systems ranging from kelp microbiomes to animal behaviour to coastal community assembly.

Acquired Photosynthesis in Marine Planktonic Communities

A model for acquired phototrophy

A schematic for acquired photosynthesis, which can be represented with a mathematical model and tested in the laboratory.

Acquired photosynthesis, in which an organism becomes a primary producer by stealing organelles or partnering with an autotrophic endosymbiont, can effectively transform planktonic community members from predators to competitors. I first became interested in this phenomenon as an undergraduate while working with Paul Falkowski at Rutgers University. In collaboration with Matt Johnson and Mike Neubert at WHOI, I’m developing and testing general theory describing the acquisition of photosynthesis. Ask me about our latest manuscript, which uses this theory to understand light-dependence and bloom dynamics in coastal planktonic communities!

Maintenance of mixotrophy by heterogeneous environments

Holly culturing oligotrophic gyre mixotrophs

Culturing oligotrophic gyre mixotrophs. Image (c) Ken Kostel / WHOI

Mixotrophs (organisms that combine photosynthesis and heterotrophy) play a critical role in the surface ocean by coupling primary production and nutrient remineralization within a single cell. In collaboration with Matt Johnson and Mike Neubert at WHOI, I am studying how the persistence of mixotrophs in more complex communities that include metabolic “specialists” depends upon environmental conditions. I am specifically interested in how environmental heterogeneity (e.g., the frequency of light-dark switching, and the periodicity of nutrient supply) affect competitive outcomes.

Partner diversity in multispecies mutualisms

Douglas-fir, Olympic National Park

Towering Douglas-fir trees in Olympic National Park are supported by a huge belowground diversity of ectomycorrhizal fungal partners.

While much mutualism theory has traditionally focused on pairwise interactions, in reality many mutualistic interactions involve guilds comprised of multiple species. How can we explain the persistence of such high levels of diversity? As a Ph.D. student, I focused in particular on the metabolic mutualism between trees and ectomycorrhizal fungi, which can involve simultaneous association of host trees with dozens of fungal species. I showed that fungal diversity can be affected by both abiotic and biotic processes at the landscape scale, can have implications for diversity, and can arise from optimal (though counterintuitive) investment by trees in low-quality partners.

Optimal control in biological systems

Tree distributing money to fungi

Which partner should I choose? Optimal control theory can help us understand how individuals choose among investments in mutualistic partners, in acquired metabolism, etc.

As a theoretical ecologist, I have particular interests in novel applications of optimal control theory in biological systems. Working with Mike Neubert at WHOI, I use optimal control theory to develop general frameworks for marine reserve design: We’ve shown that profit-maximization can sometimes depend on putting the majority (up to 80%!) of species habitat into reserve. I am also interested in optimal control theory as a way to explore the upper boundaries evolutionary trajectories: As a Ph.D. student, I used an optimal investment framework to study how partner diversity might be maintained in a multispecies mutualism.

<<Top Image: Coral goby surrounded by corals (which acquire photosynthesis through metabolic mutualisms with zooxanthellae), Kapoho Tidepools, Hawaii, August 2008>>