title: Experimental removal of sexual selection leads to decreased investment in an immune component in female Tribolium castaneum.
abstract: Because of divergent selection acting on males and females arising from different life-history strategies, polyandry can be expected to promote sexual dimorphism of investment into immune function. In previous work we have established the existence of such divergence within populations where males and females are exposed to varying degrees of polyandry. We here test whether the removal of sexual selection via enforced monogamy generates males and females that have similar levels of investment in immune function. To test this prediction experimentally, we measured differences between the sexes in a key immune measurement (phenoloxidase (PO) activity) and resistance to the microsporidian Paranosema whitei in Tribolium castaneum lines that evolved under monogamous (sexual selection absent) vs polyandrous (sexual selection present) mating systems. At generation 49, all selected lines were simultaneously assessed for PO activity and resistance to their natural parasite P. whitei after two generations of relaxed selection. We found that the polyandrous regime was associated with a clear dimorphism in immune function: females had significantly higher PO activities than males in these lines. In contrast, there was no such difference between the sexes in the lines evolving under the monogamous regime. Survival in the infection experiment did not differ between mating systems or sexes. Removing sexual selection via enforced monogamy thus seems to erase intersexual differences in immunity investment. We suggest that higher PO activities in females that have evolved under sexual selection might be driven by the increased risk of infections and/or injuries associated with exposure to multiple males.
authors.affiliation: ETH Zurich, Experimental Ecology, Institute for Integrative Biology, D-USYS, Universitätsstrasse 16, 8092 Zürich, Switzerland; School of BioSciences, University of Melbourne, 30 Flemington Road, Parkville, Victoria 3010, Australia. Electronic address: sangartner@hotmail.com.
authors.forename: Sandra
authors.initials: S
authors.lastname: Hangartner
authors.affiliation: Department of Entomology, Institute of Zoology, Jagiellonian University, Gronostajowa 9, 30-387 Kraków, Poland.
authors.forename: Łukasz
authors.initials: Ł
authors.lastname: Michalczyk
authors.affiliation: School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom.
authors.forename: Matthew J G
authors.initials: MJ
authors.lastname: Gage
authors.affiliation: ETH Zurich, Experimental Ecology, Institute for Integrative Biology, D-USYS, Universitätsstrasse 16, 8092 Zürich, Switzerland.
authors.forename: Oliver Y
authors.initials: OY
authors.lastname: Martin
mesh_terms: D000818:Animals; D005075:Biological Evolution; D060467:Disease Resistance / Q000235:genetics / Q000276:immunology; D004789:Enzyme Activation; D005260:Female; D008297:Male; D052586:Mating Preference, Animal; D014442:Monophenol Monooxygenase / Q000378:metabolism; D012641:Selection, Genetic; D014231:Tribolium / Q000235:genetics* / Q000276:immunology* / Q000378:metabolism
chemical_list: D014442:Monophenol Monooxygenase
keywords: Costs; Immunity; Nosema; Paranosema; Parasite resistance; Phenoloxidase; Reproduction; Sexual conflict; Sexual dimorphism; Trade-offs