Physiological costs enforce the honesty of lek display in the black grouse (Tetrao tetrix)
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Females may use condition-dependent sexual traits as reliable cues of male “quality” if the costs of the expression of such traits vary with male “quality”, and if there is positive genetic correlation between male traits and condition. However, there are multiple ways of measuring the changes in body condition which reflect physiological costs meaning that the multifaceted nature of the physiological costs associated with the expression of sexual traits has rarely been thoroughly examined. In the lekking black grouse (Tetrao tetrix), mating success is highly skewed towards males defending central territories and having high survival rates to the following year, but the mechanisms underpinning such superior performance remain unclear. In this study, we quantified the changes in five measures of body condition before and after the mating season and related these changes to male lek performance (fighting rate, territory centrality and mating success) to understand the physiological costs of male reproductive effort. Between the two capture sessions, male body mass decreased significantly, blood parasite counts and plasma carotenoid concentration increased substantially while the total immunoglobulin concentration tended to increase. There was no overall impairment of individual body condition as the changes in the five measures of body condition were unrelated. Male fighting rate was unrelated to changes in the condition measures but males losing more body mass defended central territories and had high mating success. Therefore, females preferring central, dominant males may select males better able to afford the energetic costs of lek performance thereby effectively enforcing the honesty of male display.
KeywordsBody mass Carotenoids Mating success Parasite load Sexual selection
This work was undertaken with the permission of the Central Finland Environmental Centre and the Animal Care committee of the University of Jyväskylä. We are grateful to Elina Virtanen, Anssi Lipponen, Sami Kyröläinen, Henna Ojaniemi, and Jouni Raninen for help in the laboratory. We also thank Tuomo Pihlaja, Tuomo Jurmu, Matti Halonen, Heikki Helle, Raimo Saunanen, Laura Häsä, and Ossi Nokelainen for field assistance. We are grateful to Tarmo Ketola, Anders Møller, Carl Soulsbury, and two anonymous reviewers for comments on earlier drafts of this manuscript. This project was founded by the Academy of Finland (Grant nos. 7211271 and 7119165). We thank the Finnish Centre of Excellence in Evolutionary Research and FNRS for funding.
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