Parasites on parasites: coupled fluctuations in stacked contact processes

TL;DR

This paper introduces a layered contact process model for host-parasite interactions, revealing complex dynamics such as nonmonotonic parasite prevalence and transitions in parasite levels, inspired by hyperparasitism and surface-growth phenomena.

Contribution

It develops a novel stacked contact process model incorporating vertical and horizontal transmission, and explores multi-level parasite dynamics with phase transitions.

Findings

Parasite prevalence varies nonmonotonically with host turnover.

Multiple parasite levels can be maintained or lost depending on parameters.

Transition between finite and infinite parasite levels resembles surface-growth roughening.

Abstract

We present a model for host-parasite dynamics which incorporates both vertical and horizontal transmission as well as spatial structure. Our model consists of stacked contact processes (CP), where the dynamics of the host is a simple CP on a lattice while the dynamics of the parasite is a secondary CP which sits on top of the host-occupied sites. In the simplest case, where infection does not incur any cost, we uncover a novel effect: a nonmonotonic dependence of parasite prevalence on host turnover. Inspired by natural examples of hyperparasitism, we extend our model to multiple levels of parasites and identify a transition between the maintenance of a finite and infinite number of levels, which we conjecture is connected to a roughening transition in models of surface-growth.