The effect of competition and horizontal trait inheritance on invasion, fixation and polymorphism

TL;DR

This paper develops a stochastic and deterministic modeling framework to study how horizontal trait transfer interacts with competition, influencing invasion, fixation, and polymorphism of traits in populations.

Contribution

It introduces a new modeling approach that combines competition and horizontal transfer effects, revealing their impact on trait dynamics and population stability.

Findings

Horizontal transfer can maintain deleterious traits in populations.

Transfer accelerates fixation when competition is weak.

Stochastic transfer significantly affects population fluctuations.

Abstract

Horizontal transfer (HT) of heritable information or `traits' (carried by genetic elements, endosymbionts, or culture) is widespread among living organisms. Yet current ecological and evolutionary theory addressing HT is limited. We present a modeling framework for the dynamics of two populations that compete for resources and exchange horizontally (transfer) an otherwise vertically inherited trait. Competition influences individual demographics, affecting population size, which feeds back on the dynamics of transfer. We capture this feedback with a stochastic individual-based model, from which we derive a deterministic approximation for large populations. The interaction between horizontal transfer and competition makes possible the stable (or bi-stable) polymorphic maintenance of deleterious traits (including costly plasmids). When transfer rates are of a general density-dependent form, transfer stochasticity contributes strongly to population fluctuations. For an initially rare trait, we describe the probabilistic dynamics of invasion and fixation. Acceleration of fixation by HT is faster when competition is weak in the resident population. Thus, HT can have a major impact on the distribution of mutational effects that are fixed, and our model provides a basis for a general theory of the influence of HT on eco-evolutionary dynamics and adaptation.