Larval size in acanthocephalan parasites: Influence of intraspecific competition and effects on intermediate host behavioural changes

Lucile Dianne,Nathalie Franceschi,Clément Lagrue,Thierry Rigaud,Loïc Bollache

doi:10.1186/1756-3305-5-166

Abstract

BackgroundParasites often face a trade-off between exploitation of host resources and transmission probabilities to the next host. In helminths, larval growth, a major component of adult parasite fitness, is linked to exploitation of intermediate host resources and is influenced by the presence of co-infecting conspecifics. In manipulative parasites, larval growth strategy could also interact with their ability to alter intermediate host phenotype and influence parasite transmission.MethodsWe used experimental infections of Gammarus pulex by Pomphorhynchus laevis (Acanthocephala), to investigate larval size effects on host behavioural manipulation among different parasite sibships and various degrees of intra-host competition.ResultsIntra-host competition reduced mean P. laevis cystacanth size, but the largest cystacanth within a host always reached the same size. Therefore, all co-infecting parasites did not equally suffer from intraspecific competition. Under no intra-host competition (1 parasite per host), larval size was positively correlated with host phototaxis. At higher infection intensities, this relationship disappeared, possibly because of strong competition for host resources, and thus larval growth, and limited manipulative abilities of co-infecting larval acanthocephalans.ConclusionsOur study indicates that behavioural manipulation is a condition-dependant phenomenon that needs the integration of parasite-related variables to be fully understood.

Highlights

Parasites often face a trade-off between exploitation of host resources and transmission probabilities to the host
Using experimental infection of G. pulex by P. laevis, we investigated whether cystacanth size modulates the intensity of host behavioural alterations
Since some parasite life-history traits vary between parasite strains, we evaluated size differences between parasite sibships and tested if these values influenced their ability to alter amphipods phototaxis

Summary

Introduction

Parasites often face a trade-off between exploitation of host resources and transmission probabilities to the host. Larval growth, a major component of adult parasite fitness, is linked to exploitation of intermediate host resources and is influenced by the presence of co-infecting conspecifics. Larval growth strategy could interact with their ability to alter intermediate host phenotype and influence parasite transmission. Many complex-life cycle parasites have developed the ability to alter the phenotype of their intermediate hosts – increasing transmission probabilities –, a phenomenon called parasitic manipulation [20,21,22,23,24]. Two studies on cestode parasites support the idea that larger larval size favours parasitic manipulation [24,25]. Whether apparent size effects on host manipulation were due to parasite age (as observed in an acanthocephalan; [26]) or if it was a direct size effect cannot be discriminated

Methods

Results

Conclusion