Weak Convergence of Non-neutral Genealogies to Kingman's Coalescent

Interacting particle populations undergoing repeated mutation and fitness-based selection steps model genetic evolution, and describe a broad class of sequential Monte Carlo methods. The genealogical tree embedded into the system is important in both applications. Under neutrality, when fitnesses of particles and their parents are independent, rescaled genealogies are known to converge to Kingman's coalescent. Recent work established convergence under non-neutrality, but only for finite-dimensional distributions. We prove weak converge of non-neutral genealogies on the space of cadlag paths under standard assumptions, enabling analysis of the whole genealogical tree. The proof relies on a conditional coupling in a random environment.