Ornstein-Uhlenbeck fluctuations for the line counting process of the ancestral selection graph

For the Moran model with strong or moderate selection we prove that the fluctuations around the deterministic limit of the line counting process of the ancestral selection graph converge to an Ornstein-Uhlenbeck process.

To this purpose we provide an extension of a functional limit theorem by Ethier and Kurtz 1986.

This result and a small adaptation of our arguments can also be used to obtain the scaling limit for the fluctuations of certain logistic branching processes.