Cooperation is a fundamental process in evolution, spanning domains of life and scales of biological organization. From social insect colonies to multicellularity to mutualistic symbioses, throughout the history of life formerly independent biological units have evolved into new integrated wholes. Like nesting Russian matryoshka dolls, within ourselves there are other selves. This poses a puzzle, though: how does natural selection favor cooperation over conflict?

The goal of my research is to understand the evolutionary processes governing cooperation in conflict in systems that involve microbes and mobile genetic elements. Using a combination of laboratory experiments and mathematical theory, I seek to test and improve social evolution theory by applying it to taxa biologically remote from the animal behavior context in which it was originally developed. Microbes are also fascinating organisms in their own right, and understanding their evolution has important implications for human health.

Cooperation among microbes

An explosion of research in recent years has shown that many important microbial phenotypes—including traits involved in pathogenicity, metabolism, and development—are cooperative. But what limits the spread of “cheater” genotypes that benefit from a cooperative trait without paying the fitness cost of producing it? What types of social interactions occur among microbes? What is the genetic basis of these interactions? How has social evolution shaped the functional biology of microbes?

Molecular endosymbionts of bacteria

Bacteria often harbor mobile genetic elements like plasmids and phage that live inside cells but can also transmit themselves infectiously among cells. I use the relationship between these elements and their bacterial hosts to study the processes that cause symbioses to evolve towards mutualism or towards parasitism.

Mobile elements often carry genes for pathogen virulence and resistance to antibiotics. This means that their evolution holds special relevance for human health, but it also creates an evolutionary puzzle: why aren’t these genes a normal, stable part of bacterial chromosomes? An underlying issue is how evolution creates genetically coherent individuals out of independent replicators.

Symbiosis and infectious disease

Symbioses are intimate associations between two species that can be good for both (mutualism) or good for one species but not the other (parasitism). Unlike cooperation within species, where kin selection provides a unifying evolutionary principle, there is no well-supported theory that explains symbiosis. When do symbioses evolve to be mutualistic and when do they evolve to be parasitic? When do infectious diseases (one kind of symbiosis) evolve to be more harmful or less harmful? Why are so many bacterial genes involved in symbiosis carried by mobile elements like plasmids and phage?