title: Dominance-related seasonal song production is unrelated to circulating testosterone in a subtropical songbird.
abstract: Circulating testosterone (T) is widely considered to play a key role in the production of sexual displays by male vertebrates. While numerous studies support a role for circulating T in promoting the production of song in male birds, this understanding is based primarily on evidence from seasonally breeding northern temperate species, leaving it unclear whether this mechanism generalizes to other regions of the world. Here we investigate whether variation in circulating levels of T can explain the marked within- and among-individual variation in male song performance observed in a subtropical population of the year-round territorial white-browed sparrow weaver (Plocepasser mahali mahali). Our findings reveal that both circulating T and male song production peaked at a similar time point, halfway through the population-level breeding season. However, while dominant males were more likely to sing and sang for longer than subordinate males, within-group paired comparisons revealed no dominance-related differences in circulating T. Moreover, comparisons both among and within individual dominant males revealed that song duration, syllable rate and proportion of time spent singing were all unrelated to circulating T. Together, our findings suggest that natural variation in male song production, at least in this population of white-browed sparrow weavers, is achieved principally through mechanisms other than variation in circulating T concentration. More widely, our results are in line with the view that male song production is not exclusively regulated by gonadally synthesized steroids.
authors.affiliation: Centre for Life and Environmental Sciences, University of Exeter, Penryn Campus, Cornwall TR10 9EZ, UK; School of Biological Sciences, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK. Electronic address: jenny.e.york@gmail.com.
authors.forename: Jenny E
authors.initials: JE
authors.lastname: York
authors.affiliation: School of Biological Sciences, Life Sciences Building, 24 Tyndall Avenue, Bristol BS8 1TQ, UK.
authors.forename: Andrew N
authors.initials: AN
authors.lastname: Radford
authors.affiliation: Behavioural Biology, The Groningen Institute for Evolutionary Life Sciences, University of Groningen, The Netherlands.
authors.forename: Bonnie
authors.initials: B
authors.lastname: de Vries
authors.affiliation: Behavioural Biology, The Groningen Institute for Evolutionary Life Sciences, University of Groningen, The Netherlands.
authors.forename: Ton G
authors.initials: TG
authors.lastname: Groothuis
authors.affiliation: Centre for Life and Environmental Sciences, University of Exeter, Penryn Campus, Cornwall TR10 9EZ, UK.
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Young
mesh_terms: D000818:Animals; D004291:Dominance-Subordination; D012739:Gonadal Steroid Hormones / Q000097:blood; D008297:Male; D012621:Seasons; D046370:Sparrows / Q000097:blood / Q000502:physiology*; D013731:Territoriality; D013739:Testosterone / Q000097:blood*; D014329:Tropical Climate; D014828:Vocalization, Animal / Q000502:physiology*
chemical_list: D012739:Gonadal Steroid Hormones; D013739:Testosterone
keywords: Circulating testosterone; Dominance; Seasonality; Sexual signalling; Tropical endocrinology