title: Dawn-song onset coincides with increased HVC androgen receptor expression but is decoupled from high circulating testosterone in an equatorial songbird.
abstract: The song of songbirds is a testosterone-sensitive behavior that is controlled by brain regions expressing androgen receptors. At higher latitudes, seasonal singing is stimulated by increasing day-length and elevated circulating testosterone. However, a large number of songbird species inhabit equatorial regions under a nearly constant photoperiod, and the neuroendocrine mechanisms of seasonal song in these species have rarely been investigated. We studied males from an equatorial population of the silver-beaked tanager (Ramphocelus carbo), an Amazonian songbird. We found seasonality in dawn-song behavior, which was displayed continuously for more than half a year throughout an extended breeding territoriality stage. The seasonal activation of dawn-song was correlated with an increased area of androgen receptor expression in HVC, a major brain area of song control. However, testosterone levels remained low for several weeks after activation of dawn-song. Circulating levels of testosterone were elevated only later in the breeding season, coinciding with a higher dawn-song output and with the mating period. Our results suggest that the seasonal activation of dawn-song and territoriality involves an increase of androgen target cells in HVC. This mechanism could potentially function to circumvent adverse effects of high testosterone levels in a species with an extended breeding season.
authors.affiliation: Department of Behavioural Neurobiology, Max Planck Institute for Ornithology, Eberhard-Gwinner-Strasse, 82319 Seewiesen, Germany. Electronic address: rquispe@orn.mpg.de.
authors.forename: René
authors.initials: R
authors.lastname: Quispe
authors.affiliation: ENES/Neuro-PSI, CNRS UMR 9197 Université Jean Monnet 23 rue Michelon, 42023 Saint-Etienne Cedex 2, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Sèbe
authors.affiliation: Universidade Federal do Pará, Laboratório de Ornitologia e Bioacústica. Rua Augusto Correa, 01-Guamá, 66075-110 Belém, PA, Brazil.
authors.forename: Maria Luisa
authors.initials: ML
authors.lastname: da Silva
authors.affiliation: Department of Behavioural Neurobiology, Max Planck Institute for Ornithology, Eberhard-Gwinner-Strasse, 82319 Seewiesen, Germany.
authors.forename: Manfred
authors.initials: M
authors.lastname: Gahr
mesh_terms: D000818:Animals; D001921:Brain / Q000502:physiology; D002909:Chronobiology Phenomena / Q000502:physiology*; D008297:Male; D017440:Photoperiod; D011944:Receptors, Androgen / Q000378:metabolism*; D012098:Reproduction / Q000502:physiology; D012621:Seasons; D020308:Songbirds / Q000378:metabolism*; D013739:Testosterone / Q000378:metabolism*; D014828:Vocalization, Animal / Q000502:physiology*
chemical_list: D011944:Receptors, Androgen; D013739:Testosterone
keywords: Annual cycle; Brain; Dawn song; Life history; Territoriality; Tropical bird