Public goods and Multicellularity
Public goods: Theory
Traditionally, the evolution of cooperation has been viewed through the lens of game theory, and in particular a game theoretic formulation of the Moran model, where fitness are mapped to game pay-offs. These models elegantly capture the "dilemma of cooperation"; mutants who defect and share the benefits of cooperation while not contributing themselves are more fit than cooperators, and should sweep through the population to fixation. Though this formulation can be an very useful tool, it can become restrictive when trying to understand the mechanistic underpinnings of a particular biological system.
My work at Princeton has focussed on taking a more ecologically grounded approach to systems that feature public goods by building models that account for system-specific population ecology. The work has followed two strands.
The first is primarily theoretical and builds on my background in stochastic processes. Investigating the impact of demographic noise on mechanistic models of public goods dynamics, I have identified a mechanism by which stochasticity can reverse the direction of selection to that predicted deterministically. In the context of public good production, demographic noise alone can thus alleviate the dilemma of cooperation:
Demographic noise can reverse the direction of deterministic selection - Proc. Nat. Acad. Sci.
Below is a simulation in which public good producers (blue) and cheating non-producers (not shown) compete in patches in space (100x100 patches). Demographic stochasticity at the patch level profoundly alters the dynamics of the system, causing public good producers to be selected for in the stochastic system (right) where they are selected against in the deterministic system (left).
This work has also been covered in popular science pieces:
Altruism has more of an evolutionary advantage than selfishness, mathematicians say - The Independent
Forget cut-throat competition: to survive, try a little selflessness, The Guardian
Chance Events Make Altruism Inevitable - IFLScience
Debunking the Selfish Myth, Positive News
Public goods: Experiment
The second strand is firmly rooted in empirical research. In collaboration with a team of experimental biologists, I built mathematical models of public goods production in the nematode C. elegans:
Farming and public goods production in Caenorhabditis elegans populations - Proc. Natl. Acad. Sci.
Fascinatingly, we found that the worms engage in a form of primitive agriculture, driven by their foraging behavior. Having visited a bacterial food source, certain C. elegans strains redistributing the bacteria, which subsequently grows. This is demonstrated below, where bacteria (green) can be seen to be redistributed along worm trails leading away from the initial bacterial patch (red dashed circle).
Multicellularity
The evolution of organisms from individual units to complexes takes place at many scales, from the microscopic (unicellular to multicellular) to macroscopic (asocial to eusocial). Typically this involves one of two processes: coming together, where separate (possibly unrelated) individuals come together to form a new complex, or staying together, where the progeny of a reproductive event remains part of its parent complex.
I am currently conducting theoretical investigations into the ecological conditions which might favour either route to multicellularity.