General selection models: Bernstein duality and minimal ancestral structures

TL;DR

This paper extends the Wright-Fisher model with frequency-dependent selection, introduces Bernstein duality, and characterizes minimal ancestral structures, providing new tools for understanding genealogies in population genetics.

Contribution

It develops a novel duality framework called Bernstein duality and characterizes minimal ancestral structures in frequency-dependent selection models.

Findings

Generalization of the ancestral selection graph

Introduction of Bernstein duality for forward-backward process relation

Characterization of minimal ancestral processes

Abstract

$\Lambda$-Wright--Fisher processes provide a robust framework to describe the type-frequency evolution of an infinite neutral population. We add a polynomial drift to the corresponding stochastic differential equation to incorporate frequency-dependent selection. A decomposition of the drift allows us to approximate the solution of the stochastic differential equation by a sequence of Moran models. The genealogical structure underlying the Moran model leads in the large population limit to a generalisation of the ancestral selection graph of Krone and Neuhauser. Building on this object, we construct a continuous-time Markov chain and relate it to the forward process via a new form of duality, which we call Bernstein duality. We adapt classical methods based on the moment duality to determine the time to absorption and criteria for the accessibility of the boundaries; this extends a recent result by Gonz\'alez Casanova and Span\`o. An intriguing feature of the construction is that the same forward process is compatible with multiple backward models. In this context we introduce suitable notions for minimality among the ancestral processes and characterise the corresponding parameter sets. In this way we recover classic ancestral structures as minimal ones.