Multiple host use and the dynamics of host switching in host–parasite systems

Thomas Hovestadt,Oliver Mitesser,Karsten Schönrogge,Jeremy A Thomas

doi:10.1111/icad.12374

Abstract

Abstract The link between multi‐host use and host switching in host–parasite interactions is a continuing area of debate. Lycaenid butterflies in the genus Maculinea, for example, exploit societies of different Myrmica ant species across their ranges, but there is only rare evidence that they simultaneously utilise multiple hosts at a local site, even where alternative hosts are present. We present a simple population‐genetic model accounting for the proportion of two alternative hosts and the fitness of parasite genotypes on each host. In agreement with standard models, we conclude that simultaneous host use is possible whenever fitness of heterozygotes on alternative hosts is not too low. We specifically focus on host‐shifting dynamics when the frequency of hosts changes. We find that (i) host shifting may proceed so rapidly that multiple host use is unlikely to be observed, (ii) back and forth transition in host use can exhibit a hysteresis loop, (iii) the parasites' host use may not be proportional to local host frequencies and be restricted to the rarer host under some conditions, and (iv) that a substantial decline in parasite abundance may typically precede a shift in host use. We conclude that focusing not just on possible equilibrium conditions but also considering the dynamics of host shifting in non‐equilibrium situations may provide added insights into host–parasite systems.

Highlights

Host–parasite interactions are ubiquitous across ecosystems and are widely recognised as important drivers of dynamic evolutionary change, a perspective that inspired the Red Queen hypothesis (van Valen, 1973), the idea that parasitism promotes recombination and sex (e.g. Hamilton, 1980; Bell & Smith, 1987; Salathé et al, 2008) and the concept of the geographic mosaic of coevolution (Thompson, 2009)
We present a simple population-genetic model accounting for the proportion of two alternative hosts and the fitness of parasite genotypes on each host
The argumentation provided will apply if alternative hosts were not different host species but just distinct host genotypes, e.g. genotypes with different CHC profiles; such profiles play a great role in the nest-mate recognition of social insects (Howard & Blomquist, 2005)

Summary

Introduction

Bailey et al, 2009) with frequent shifting from one host to another (Hardy & Cook, 2010). In natural landscapes or metapopulations that are dynamic and stochastic, where immigration of host and parasites from other sites occurs continuously, and where the abundances of the alternative host species may continuously change, it may be more informative to investigate how the presence of a heterozygote disadvantage affects the timing and dynamics of transitions from using one host to another To explore these questions in more detail, we provide a simple model of a local host–parasite population that is linked to an external world by immigration. The range of value for R covers a fair spectrum of net-fertility values reported for insects (Hassell et al, 1976), wX,xy values cover the whole possible spectrum and values for immigration rate, and Ixx/K cover a range as it may occur in metapopulations without being so large as to create panmictic populations

Results

Findings

Discussion