Elevated spring testosterone increases parasite intensity in male red grouse |
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Authors: | Mougeot Francois; Redpath Stephen M; Piertney Stuart B |
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Institution: | a Centre for Ecology and Hydrology, Hill of Brathens, Banchory, AB31 4BW, Scotland, UK, b Instituto de Investigaciones en Recursos Cinegeticos (CSIC-UCLM-JCCM), Ronda de Toledo s/n, 13005 Ciudad Real, Spain, and c Natural Environment Research Council Molecular Genetics in Ecology Initiative, School of Biological Sciences, University of Aberdeen, Aberdeen AB24 2TZ, UK |
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Abstract: | The expression of testosterone-dependent sexual traits mightsignal the ability of their bearers to cope with parasite infections.According to the immunocompetence handicap hypothesis (IHH),such signals would be honest because physiological costs oftestosterone, such as a reduced ability to control parasiteinfections, would prevent cheating. We tested whether testosteronewould affect the outcome of a standardized parasite challengein red grouse, using a main parasite of the species, the nematodeTrichostrongylus tenuis. We caught males in spring, removedtheir nematode parasites, and implanted them with testosteroneor empty implants, as controls. After 1 month, they were reinfectedwith a standard dose of infective T. tenuis parasites. Whenchallenged, testosterone males had relatively less globulinrelative to albumin plasma proteins than control males, an indicationthat they had experienced increased physiological stress. Testosterone-treatedmales had significantly more T. tenuis parasites than controlsin the next autumn and also had more coccidia and lost moreweight than controls. Testosterone-treated males neverthelessbenefited from their elevated spring testosterone: they hadbigger sexual ornaments than controls both in spring and autumn,and they tended to have a higher pairing and breeding successthan controls. Our results supported the IHH in showing thatelevated testosterone impaired the ability of males to copewith a standardized challenge by a dominant parasite. Testosteronethus plays a key role in mediating trade-offs between reproductiveactivities and parasite defense, and testosterone-dependentcomb size might honestly signal the ability of red grouse tocontrol T. tenuis infection. |
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Keywords: | coccidia immunocompetence parasite red grouse sexual selection testosterone trade-off Trichostrongylus tenuis |
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