Limited role of spatial self-structuring in emergent trade-offs during pathogen evolution

TL;DR

This study reexamines how spatial self-structuring influences pathogen transmission-virulence trade-offs, revealing that mobility often disrupts these patterns, but metapopulation dynamics can restore them.

Contribution

It analytically characterizes conditions for emergent trade-offs due to spatial patterns and explores how host mobility affects these dynamics.

Findings

Spatial self-structuring can lead to emergent trade-offs.

Host mobility often destroys spatial patterns and trade-offs.

Metapopulation dynamics can restore trade-offs by preventing pathogen extinction.

Abstract

Pathogen transmission and virulence are main evolutionary variables broadly assumed to be linked through trade-offs. In well-mixed populations, these trade-offs are often ascribed to physiological restrictions, while populations with spatial self-structuring might evolve emergent trade-offs. Here, we reexamine a model of the latter kind proposed by Ballegooijen and Boerlijst with the aim of characterising the mechanisms causing the emergence of the trade-off and its structural robustness. Using invadability criteria, we establish the conditions under which an evolutionary feedback between transmission and virulence mediated by pattern formation can poise the system to a critical boundary separating a disordered state (without emergent trade-off) from a self-structured phase (where the trade-off emerges), and analytically calculate the functional shape of the boundary in a certain approximation. Beyond evolutionary parameters, the success of an invasion depends on the size and spatial structure of the invading and invaded populations. Spatial self-structuring is often destroyed when hosts are mobile, changing the evolutionary dynamics to those of a well-mixed population. In a metapopulation scenario, the systematic extinction of the pathogen in the disordered phase may counteract the disruptive effect of host mobility, favour pattern formation and therefore recover the emergent trade-off.