title: Expression of parasite genetic variation changes over the course of infection: implications of within-host dynamics for the evolution of virulence.
abstract: How infectious disease agents interact with their host changes during the course of infection and can alter the expression of disease-related traits. Yet by measuring parasite life-history traits at one or few moments during infection, studies have overlooked the impact of variable parasite growth trajectories on disease evolution. Here we show that infection-age-specific estimates of host and parasite fitness components can reveal new insight into the evolution of parasites. We do so by characterizing the within-host dynamics over an entire infection period for five genotypes of the castrating bacterial parasite Pasteuria ramosa infecting the crustacean Daphnia magna. Our results reveal that genetic variation for parasite-induced gigantism, host castration and parasite spore loads increases with the age of infection. Driving these patterns appears to be variation in how well the parasite maintains control of host reproduction late in the infection process. We discuss the evolutionary consequences of this finding with regard to natural selection acting on different ages of infection and the mechanism underlying the maintenance of castration efficiency. Our results highlight how elucidating within-host dynamics can shed light on the selective forces that shape infection strategies and the evolution of virulence.
authors.affiliation: Institute of Evolutionary Biology, University of Edinburgh, Ashworth Labs, Charlotte Auerbach Road, Edinburgh EH9 3FL, UK Zoological Institute, University of Basel, Vesalgasse 1, Basel 4051, Switzerland m.clerc@sms.ed.ac.uk.
authors.forename: Melanie
authors.initials: M
authors.lastname: Clerc
authors.affiliation: Zoological Institute, University of Basel, Vesalgasse 1, Basel 4051, Switzerland.
authors.forename: Dieter
authors.initials: D
authors.lastname: Ebert
authors.affiliation: Zoological Institute, University of Basel, Vesalgasse 1, Basel 4051, Switzerland School of Biological Sciences, Monash University, Melbourne 3800, Australia.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Hall
mesh_terms: D000818:Animals; D003621:Daphnia / Q000382:microbiology*; D019143:Evolution, Molecular; D014644:Genetic Variation; D054884:Host-Pathogen Interactions / Q000502:physiology*; D058676:Pasteuria / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology*
keywords: Daphnia; Pasteuria ramosa; genetic variation; host–parasite interactions; life history