title: Larval size in acanthocephalan parasites: influence of intraspecific competition and effects on intermediate host behavioural changes.
abstract: BACKGROUND
  Parasites 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.
  
  
  METHODS
  We 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.
  
  
  RESULTS
  Intra-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.
  
  
  CONCLUSIONS
  Our study indicates that behavioural manipulation is a condition-dependant phenomenon that needs the integration of parasite-related variables to be fully understood.
authors.affiliation: Equipe Ecologie Evolutive, UMR CNRS 6282 Biogéosciences, Université de Bourgogne, 6 Boulevard Gabriel, 21000 Dijon, France. lucile.dianne@u-bourgogne.fr
authors.forename: Lucile
authors.initials: L
authors.lastname: Dianne
authors.forename: Loïc
authors.initials: L
authors.lastname: Bollache
authors.forename: Clément
authors.initials: C
authors.lastname: Lagrue
authors.forename: Nathalie
authors.initials: N
authors.lastname: Franceschi
authors.forename: Thierry
authors.initials: T
authors.lastname: Rigaud
mesh_terms: D000049:Acanthocephala / Q000033:anatomy & histology* / Q000502:physiology*; D000818:Animals; D003445:Crustacea / Q000469:parasitology*; D006790:Host-Parasite Interactions; D007814:Larva / Q000033:anatomy & histology / Q000502:physiology; D013045:Species Specificity