title: Atlantic salmon infected with salmon lice are more susceptible to new lice infections.
abstract: Aggregation is commonly observed for macroparasites, but its adaptive value remains unclear. Heavy infestations intensities may lead to a decrease in some fitness-related traits of parasites (e.g. parasite fecundity or survival). However, to a dioecious parasite, increased aggregation could also increase the chance of finding individuals of the opposite sex. In a laboratory experiment, we tested if previous experience with salmon lice (Lepeophtheirus salmonis) affected susceptibility of Atlantic salmon (Salmo salar) to later exposure to the same parasite species. We found that currently infected fish got higher intensities of new lice than naive fish. This suggests that hosts already carrying parasites are more susceptible to new lice infections. For this dioecious parasite, such positive density dependence might be adaptive, ensuring successful reproduction under conditions of low lice densities by increasing the probability of both sexes infecting the same host.
authors.affiliation: Department of Biology, University of Bergen, Bergen, Norway.
authors.forename: M S
authors.initials: MS
authors.lastname: Ugelvik
authors.affiliation: Department of Biology, University of Bergen, Bergen, Norway.
authors.forename: T
authors.initials: T
authors.lastname: Mo
authors.affiliation: Department of Biology, University of Bergen, Bergen, Norway.|Ecologie et Dynamique des Systèmes Anthropisés (FRE 3498), CNRS/Université de Picardie Jules Verne, Amiens, France.
authors.forename: A
authors.initials: A
authors.lastname: Mennerat
authors.affiliation: Department of Biology, University of Bergen, Bergen, Norway.
authors.forename: A
authors.initials: A
authors.lastname: Skorping
mesh_terms: D000818:Animals; D033342:Copepoda / Q000502:physiology*; D004198:Disease Susceptibility / Q000469:parasitology / Q000662:veterinary; D004478:Ectoparasitic Infestations / Q000469:parasitology / Q000662:veterinary*; D005260:Female; D005393:Fish Diseases / Q000469:parasitology*; D006790:Host-Parasite Interactions; D008297:Male; D012098:Reproduction; D020317:Salmo salar
keywords: 
  Lepeophtheirus salmonis
  ; 
  Salmo salar
  ; aggregation; positive density dependence; susceptibility