Rethinking Population Bottlenecks: Intrinsic Fluctuations, Mutation and Dynamical Demographic Phases

Abstract

By abruptly changing the size and composition of a population, bottlenecks can dramatically alter evolutionary trajectories. In the traditional picture, the faster a population recovers from a bottleneck, the more rapidly finite-size intrinsic fluctuations are suppressed and therefore the greater the likelihood of fixation to the attractor within whose basin the bottleneck constrained the population, initially. We now argue that this intuition is misleading; demonstrating that precisely the opposite behaviour is also possible. Depending critically on the rate of mutation, increased population growth can drive fixation to attractors that are different to that from whose basin it started. These findings are explained in terms of statistically distinct regimes of demographic behaviour, drawing parallels with the notion of non-equilibrium phase transitions. Such dynamical demographic phases are delimited by sharp transitions in time, as a population grows, and ultimately result from a time-dependent antagonism between mutation and the stochastically-induced effects of frequency-dependent birth.