title: Cortisol but not testosterone is repeatable and varies with reproductive effort in wild red deer stags.
abstract: Although it is known that hormone concentrations vary considerably between individuals within a population, how they change across time and how they relate to an individual's reproductive effort remains poorly quantified in wild animals. Using faecal samples collected from wild red deer stags, we examined sources of variation in faecal cortisol and androgen metabolites, and the potential relationship that these might have with an index of reproductive effort. We also biologically validated an assay for measuring androgen metabolites in red deer faeces. We show that variation in hormone concentrations between samples can be accounted for by the age of the individual and the season when the sample was collected. Faecal cortisol (but not androgen) metabolites also showed significant among-individual variation across the 10-year sampling time period, which accounted for 20% of the trait's phenotypic variance after correcting for the age and season effects. Finally, we show that an index of male reproductive effort (cumulative harem size) during the mating season (rut) was positively correlated with male cortisol concentrations, both among and within individuals. We suggest that the highest ranking males have the largest cumulative harem sizes (i.e. invest the greatest reproductive effort), and that this social dominance may have associated behaviours such as increased frequency of agonistic interactions which are associated with corresponding high levels of faecal cortisol metabolites (FCM).
authors.affiliation: Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3FL, UK. Electronic address: a.pavitt@sms.ed.ac.uk.
authors.forename: Alyson T
authors.initials: AT
authors.lastname: Pavitt
authors.affiliation: Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3FL, UK.
authors.forename: Craig A
authors.initials: CA
authors.lastname: Walling
authors.affiliation: Department of Biomedical Sciences, University of Veterinary Medicine, Veterinärplatz 1, A-1210 Vienna, Austria.
authors.forename: Erich
authors.initials: E
authors.lastname: Möstl
authors.affiliation: Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3FL, UK.
authors.forename: Josephine M
authors.initials: JM
authors.lastname: Pemberton
authors.affiliation: Institute of Evolutionary Biology, School of Biological Sciences, University of Edinburgh, Edinburgh EH9 3FL, UK; Division of Evolution, Ecology & Genetics, Research School of Biology, The Australian National University, ACT 2601, Australia.
authors.forename: Loeske E B
authors.initials: LE
authors.lastname: Kruuk
mesh_terms: D000728:Androgens / Q000737:chemistry*; D000818:Animals; D001681:Biological Assay; D003670:Deer; D006854:Hydrocortisone / Q000378:metabolism*; D008297:Male; D012098:Reproduction; D013739:Testosterone / Q000378:metabolism*
chemical_list: D000728:Androgens; D013739:Testosterone; D006854:Hydrocortisone
keywords: Androgens; Biological assay validation; Dominance; Faecal hormone metabolites; Glucocorticoids; Repeatability; Rut; Seasonal cycles