Does resource availability affect host manipulation? – an experimental test with Schistocephalus solidus

Nina Hafer,Daniel P Benesh

doi:10.1017/pao.2015.3

Abstract

SUMMARYHost manipulation is a common strategy of parasites employed to increase their fitness by changing the phenotype of their hosts. Whether host manipulation might be affected by environmental factors such as resource availability, has received little attention. We experimentally infected laboratory-bred copepods with the cestodeSchistocephalus solidus, submitted infected and uninfected copepods to either a high or a low food treatment, and measured their behaviour. Infection reduced host activity and speed in both feeding treatments. However, the difference between the infected and uninfected copepods was smaller under low food conditions, because uninfected, but not infected, copepods moved slower under these conditions. We suggest that these differences are mediated by the physical condition of copepods rather than changes in how strongly the parasite manipulated host behaviour. Additionally, we measured three fitness-relevant traits (growth, development and infection rate in the next host) of the parasite to identify potential trade-offs with host manipulation. The largest parasites in copepods appeared the least manipulative, i.e. their hosts showed the smallest behavioural alterations, but this may again reflect variation in copepod condition, rather than life history trade-offs between parasite growth and host manipulation. Our results point to the possibility that parasite transmission depends on environmental conditions.

Highlights

The environment organisms experience is rarely uniform; it varies over time and space
Host manipulation is a common strategy of parasites employed to increase their fitness by changing the phenotype of their hosts
Whether host manipulation might be affected by environmental factors such as resource availability, has received little attention

Summary

Introduction

The environment organisms experience is rarely uniform; it varies over time and space. Environmental stressors can reshape host–parasite interactions in various ways depending on the species and stressors involved (Lafferty and Kuris, 1999) Many parasites enhance their fitness by changing the behaviour of their host (reviewed by Holmes and Bethel, 1972; Poulin and Thomas, 1999; Moore, 2002, 2013; Poulin, 2010). Such host manipulation is well-known in complex life cycle parasites, where it serves to enhance transmission to a target host (predation enhancement), and to avoid fatal predation before the parasite reaches infectivity (predation suppression) (Hammerschmidt et al 2009; Parker et al 2009; Dianne et al 2011; Thomas et al 2011; Weinreich et al 2013). Biotic factors such as predator cues (e.g. Jakobsen and Wedekind, 1998; Baldauf et al 2007; Durieux et al 2012; Dianne et al 2014) or

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Conclusion