Department of Biology, University of Washington, Seattle, WA 98195, USA.
Gen Comp Endocrinol. 2010 May 1;166(3):581-9. doi: 10.1016/j.ygcen.2010.01.011. Epub 2010 Jan 13.
Previous work shows that most birds breeding in northern temperate regions adjust production of testosterone in response to stage of the breeding cycle and in some cases following social interactions. In contrast, prior research suggests that tropical breeding birds are less likely to modulate testosterone in response to social interactions (the propensity to increase testosterone in response to social instability is known as the challenge hypothesis). To further test the challenge hypothesis in tropical birds, we investigated whether variation in season affects reproductive condition, aggressive behavior, and social modulation of testosterone in two populations of Costa Rican rufous-collared sparrow, Zonotrichia capensis costaricensis. We conducted our study at three distinct times of year: the dry season (March and May); the veranillo, a hiatus in the rainy season (July); and the late rainy season (November). Significantly more birds were in breeding condition in the dry season than in the rainy season or veranillo. In each time period, we collected baseline testosterone samples and conducted simulated territorial intrusions (STIs). Our study shows that testosterone is modulated with season independent of breeding condition, as testosterone levels were affected by season, breeding condition, and an interaction of the two factors. Males breeding in the dry season had higher plasma testosterone levels than non-breeding males in the dry season and both breeding and non-breeding males in the veranillo and rainy season. Males did not socially modulate testosterone in any season. Aggressive behaviors expressed during STIs did not differ among seasons with the exception that males sang fewer songs during the rainy season.
先前的研究表明，大多数在北温带繁殖的鸟类会根据繁殖周期的阶段以及在某些情况下根据社交互动来调节睾丸激素的产生。相比之下，先前的研究表明，热带繁殖的鸟类不太可能根据社交互动来调节睾丸激素（根据社交不稳定程度增加睾丸激素的倾向被称为挑战假说）。为了在热带鸟类中进一步检验挑战假说，我们研究了季节变化是否会影响哥斯达黎加红颈丛雀（Zonotrichia capensis costaricensis）两个种群的繁殖状况、攻击行为以及睾丸激素的社交调节。我们在一年中的三个不同时间进行了研究：旱季（三月和五月）；旱季和雨季之间的间歇期——veranillo（七月）；以及雨季后期（十一月）。旱季的繁殖鸟类明显多于雨季或 veranillo。在每个时期，我们收集了基础睾丸激素样本并进行了模拟领地入侵（STI）。我们的研究表明，睾丸激素的季节性调节与繁殖状况无关，因为睾丸激素水平受到季节、繁殖状况以及这两个因素的相互作用的影响。在旱季繁殖的雄性的血浆睾丸激素水平高于旱季非繁殖雄性和旱季和雨季非繁殖雄性。在任何季节，雄性都没有社交调节睾丸激素。在 STI 期间表达的攻击行为在季节之间没有差异，但雄性在雨季的歌声较少。
