title: Sex-specific effects of a parasite evolving in a female-biased host population.
abstract: BACKGROUND
  Males and females differ in many ways and might present different opportunities and challenges to their parasites. In the same way that parasites adapt to the most common host type, they may adapt to the characteristics of the host sex they encounter most often. To explore this hypothesis, we characterized host sex-specific effects of the parasite Pasteuria ramosa, a bacterium evolving in naturally, strongly, female-biased populations of its host Daphnia magna.
  
  
  RESULTS
  We show that the parasite proliferates more successfully in female hosts than in male hosts, even though males and females are genetically identical. In addition, when exposure occurred when hosts expressed a sexual dimorphism, females were more infected. In both host sexes, the parasite causes a similar reduction in longevity and leads to some level of castration. However, only in females does parasite-induced castration result in the gigantism that increases the carrying capacity for the proliferating parasite.
  
  
  CONCLUSIONS
  We show that mature male and female Daphnia represent different environments and reveal one parasite-induced symptom (host castration), which leads to increased carrying capacity for parasite proliferation in female but not male hosts. We propose that parasite induced host castration is a property of parasites that evolved as an adaptation to specifically exploit female hosts.
authors.affiliation: University of Basel, Zoological Institute, Vesalgasse 1, 4051 Basel, Switzerland. david.duneau@gmail.com
authors.forename: David
authors.initials: D
authors.lastname: Duneau
authors.forename: Pepijn
authors.initials: P
authors.lastname: Luijckx
authors.forename: Ludwig F
authors.initials: LF
authors.lastname: Ruder
authors.forename: Dieter
authors.initials: D
authors.lastname: Ebert
mesh_terms: D000818:Animals; D015982:Bias; D002452:Cell Count; D003621:Daphnia / Q000033:anatomy & histology / Q000382:microbiology* / Q000469:parasitology*; D005260:Female; D006790:Host-Parasite Interactions / Q000502:physiology*; D008297:Male; D010271:Parasites / Q000254:growth & development*; D058676:Pasteuria / Q000254:growth & development*; D012727:Sex Characteristics; D013094:Spermatozoa / Q000166:cytology / Q000382:microbiology / Q000469:parasitology; D013171:Spores, Bacterial / Q000254:growth & development; D016019:Survival Analysis