Mass Extinctions & Evolutionary Lineages: A Coalescent-Theory Approach in an Agent-Based Model

In an agent-based model of evolutionary dynamics, which has been shown to undergo a nonequilibrium phase transition from extinction to survival, we apply principles of coalescent theory to investigate the responses of population lineages to simulated mass extinctions of various depths and durations. In the model, organisms reproduce via assortative mating on a neutral fitness landscape; the parameters that control the phase transition include: the mutability (distance offspring may be distributed relative to their parents in the fitness landscape) and the death parameter (percentage of organisms randomly removed during each generation). By changing the death parameter, mass extinctions can be simulated by both both “pulse” and “press” events. Lineage structure can be characterized using the time to most recent common ancestor (TMRCA) as well as a forward-in-time lineage analysis. We examine how these measures are affected by mass extinction applied in the critical regime of the phase transition, as opposed to in the survival regime. We will discuss implications of these results for population recovery and evolutionary rescue.