From subcellular structures to ecological communities, life is organized in compartments and modules specialized to perform only specific tasks, and not others. How does this division of labor come about, and what determines if species cooperate in a specialized or generalized fashion?
One theory, called the Black Queen Hypothesis, suggests that loss of functionality can occur due to selfish mutations where individuals cheat to reduce their output. This can then form the basis for mutualistic relationships, where different kind of cheaters become dependent on one another. However, from this consideration alone, one expects that specialists always eventually dominate a population of generalists. How should we then explain the persistence of generalists in nature? And how do we explain the coexistence of various combinations of generalists, specialists, and cheaters within one niche?
To address these questions, Assistant Professor Dervis Can Vural and his student Gurdip Uppal turned to basic physics. They developed models that took into account the laws of fluid dynamics, diffusion of chemicals, and microbial growth. In these models, microbes naturally self-aggregated and then evolved different modes of cooperation. The size, and shape of the groups as well as the structure of “economic exchanges” turned out to depend sensitively on the physical parameters defining the fluid as well as its motion. Then they analyzed the evolutionary transitions between generalized and specialized interactions within these clusters as well as the competitive interactions across clusters for different fluid flow patterns, diffusion lengths, molecular decay constants, and cell growth kinetics. Physical factors were as influential as fitness economics in governing the evolution of community interactions.
Vural and Uppal found physical conditions that counteract economic game theoretical expectations and established physical factors that allow generalists to resist specialization, and generalists and specialists to resist cheaters. They also determined the parameter range that allowed for multiple cooperative modes stably coexist within the same fluid niche. As such, we can view division of labor as a mechanical phenomenon, dictated by the physics of the habitat, as much as an economical one.