title: Starvation reveals the cause of infection-induced castration and gigantism.
abstract: Parasites often induce life-history changes in their hosts. In many cases, these infection-induced life-history changes are driven by changes in the pattern of energy allocation and utilization within the host. Because these processes will affect both host and parasite fitness, it can be challenging to determine who benefits from them. Determining the causes and consequences of infection-induced life-history changes requires the ability to experimentally manipulate life history and a framework for connecting life history to host and parasite fitness. Here, we combine a novel starvation manipulation with energy budget models to provide new insights into castration and gigantism in the Daphnia magna-Pasteuria ramosa host-parasite system. Our results show that starvation primarily affects investment in reproduction, and increasing starvation stress reduces gigantism and parasite fitness without affecting castration. These results are consistent with an energetic structure where the parasite uses growth energy as a resource. This finding gives us new understanding of the role of castration and gigantism in this system, and how life-history variation will affect infection outcome and epidemiological dynamics. The approach of combining targeted life-history manipulations with energy budget models can be adapted to understand life-history changes in other disease systems.
authors.affiliation: Department of Biology, Queen's University, Kingston, Ontario, Canada cressler@queensu.ca.
authors.forename: Clayton E
authors.initials: CE
authors.lastname: Cressler
authors.affiliation: Department of Biology, Queen's University, Kingston, Ontario, Canada.
authors.forename: William A
authors.initials: WA
authors.lastname: Nelson
authors.affiliation: Department of Biology, Queen's University, Kingston, Ontario, Canada Department of Mathematics and Statistics, Queen's University, Kingston, Ontario, Canada.
authors.forename: Troy
authors.initials: T
authors.lastname: Day
authors.affiliation: Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Edward
authors.initials: E
authors.lastname: McCauley
mesh_terms: D000222:Adaptation, Physiological; D000818:Animals; D018407:Bacterial Physiological Phenomena; D049628:Body Size; D003621:Daphnia / Q000254:growth & development / Q000382:microbiology* / Q000502:physiology*; D005260:Female; D005298:Fertility / Q000502:physiology; D054884:Host-Pathogen Interactions / Q000502:physiology*; D058676:Pasteuria / Q000472:pathogenicity*; D013217:Starvation
keywords: castration; gigantism; host–parasite interaction; life history; starvation