GELIFES Seminars - Rutger Hermsen

Rutger Hermsen (Utrecht University)

Quantifying natural selection at all spatial scales

Evolutionary adaptation is often the resultant of many processes that occur at different spatial scales. Consequently, selection pressures at different scales are not necessarily aligned. We present a new mathematical framework that defines and quantifies natural selection at each spatial scale. We illustrate these mathematical tools in the context of two simple computational models. The first model simulates the evolution of the infectivity of a pathogen in a spatial population. Our analysis establishes that selection pressures at different scales point in opposing directions; the result is the evolution of collective restraint. The second model simulates the evolution of cooperation in a model in which the different interactions between organisms (resource competition and cooperation) each have a different range. In this model, sufficiently cooperative organisms self-organize into discrete colonies that themselves reproduce by budding. Within colonies, selection favors cheaters; on the long run, each colony therefore faces a tragedy of the commons. Globally, however, cooperation is nevertheless victorious, because more cooperative colonies tend to bud more frequently. The mathematical analysis is able to measure this discrepancy between within-colony selection and among-colony selection quantitatively.