title: Demasculinization of male guppies increases resistance to a common and harmful ectoparasite.
abstract: Parasites are detrimental to host fitness and therefore should strongly select for host defence mechanisms. Yet, hosts vary considerably in their observed parasite loads. One notable source of inter-individual variation in parasitism is host sex. Such variation could be caused by the immunomodulatory effects of gonadal steroids. Here we assess the influence of gonadal steroids on the ability of guppies (Poecilia reticulata) to defend themselves against a common and deleterious parasite (Gyrodactylus turnbulli). Adult male guppies underwent 31 days of artificial demasculinization with the androgen receptor-antagonist flutamide, or feminization with a combination of flutamide and the synthetic oestrogen 17 β-estradiol, and their parasite loads were compared over time to untreated males and females. Both demasculinized and feminized male guppies had lower G. turnbulli loads than the untreated males and females, but this effect appeared to be mainly the result of demasculinization, with feminization having no additional measurable effect. Furthermore, demasculinized males, feminized males and untreated females all suffered lower Gyrodactylus-induced mortality than untreated males. Together, these results suggest that androgens reduce the ability of guppies to control parasite loads, and modulate resistance to and survival from infection. We discuss the relevance of these findings for understanding constraints on the evolution of resistance in guppies and other vertebrates.
authors.affiliation: Department of Biology,McGill University,1205 Dr. Penfield Av.,Montreal,H3A 1B1,QC,Canada.
authors.forename: Felipe
authors.initials: F
authors.lastname: Dargent
authors.affiliation: Department of Biology,McGill University,1205 Dr. Penfield Av.,Montreal,H3A 1B1,QC,Canada.
authors.forename: Adam R
authors.initials: AR
authors.lastname: Reddon
authors.affiliation: Department of Biology,McGill University,1205 Dr. Penfield Av.,Montreal,H3A 1B1,QC,Canada.
authors.forename: William T
authors.initials: WT
authors.lastname: Swaney
authors.affiliation: Department of Biology,McGill University,1205 Dr. Penfield Av.,Montreal,H3A 1B1,QC,Canada.
authors.forename: Gregor F
authors.initials: GF
authors.lastname: Fussmann
authors.affiliation: Department of Biology,McGill University,1205 Dr. Penfield Av.,Montreal,H3A 1B1,QC,Canada.
authors.forename: Simon M
authors.initials: SM
authors.lastname: Reader
authors.affiliation: Institute of Parasitology and Centre for Host-Parasite Interactions, McGill University,21111 Lakeshore Road,Ste-Anne de Bellevue,H9X 3V9,QC,Canada.
authors.forename: Marilyn E
authors.initials: ME
authors.lastname: Scott
authors.affiliation: Department of Biology,Carleton University,1125 Colonel By Drive,Ottawa,K1S 5B6,ON,Canada.
authors.forename: Mark R
authors.initials: MR
authors.lastname: Forbes
mesh_terms: D000726:Androgen Antagonists / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D060467:Disease Resistance / Q000502:physiology; D004359:Drug Therapy, Combination; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D005393:Fish Diseases / Q000276:immunology / Q000469:parasitology*; D005485:Flutamide / Q000008:administration & dosage / Q000494:pharmacology; D008297:Male; D059208:Parasite Load / Q000662:veterinary; D010986:Platyhelminths / Q000276:immunology*; D011036:Poecilia / Q000469:parasitology*; D011897:Random Allocation; D012737:Sex Factors; D014201:Trematode Infections / Q000276:immunology / Q000469:parasitology / Q000662:veterinary*
chemical_list: D000726:Androgen Antagonists; D004958:Estradiol; D005485:Flutamide
keywords: Gyrodactylus; Poecilia reticulata; feminization; fish; gonadal steroids; sex-biased parasitism; testosterone