Moore Ignacio T, Walker Brian G, Wingfield John C
Department of Biology, Box 351800, University of Washington, Seattle, WA 98195, USA.
Gen Comp Endocrinol. 2004 Jan 15;135(2):223-9. doi: 10.1016/j.ygcen.2003.09.012.
Territorial aggression, exhibited by male vertebrates in a reproductive context, is generally thought to be mediated by elevated levels of the gonadal steroid hormone testosterone. Rufous-collared sparrows from Papallacta, Ecuador are only aggressive during the breeding season when plasma testosterone concentrations are elevated. However, previous experiments have determined that during the breeding season testosterone does not increase in response to territorial challenges and testosterone implants do not make males more aggressive. This relationship between testosterone and aggression is different from closely related northern latitude species. We conducted another experiment investigating the role of testosterone in mediating territorial aggression, during the breeding season, in male rufous-collared sparrows. We predicted that blocking the actions of the testosterone would suppress aggression in response to territorial challenges. During the early breeding season males were captured using a simulated territorial intrusion and there was no relationship between time to capture and plasma testosterone, dihydrotestosterone, and corticosterone concentrations. Individual males were then implanted with both the aromatase inhibitor ATD and the anti-androgen Flutamide or empty implants as a control. After one week, birds were challenged with a simulated territorial intrusion and the aggressive responses measured. There were no differences in individual behavioral responses (number of songs, flights, closest approach, or time within 5 m) or overall aggression between the two groups. Androgen levels were elevated, post-implant, in the experimental group suggesting that the treatment was successful by blocking the negative feedback system. We conclude that pharmacologically inhibiting testosterone during the breeding season does not affect territorial aggression in these birds.
雄性脊椎动物在繁殖期表现出的领地攻击性通常被认为是由性腺类固醇激素睾酮水平升高介导的。来自厄瓜多尔帕帕拉卡塔的棕颈雀鹀仅在繁殖季节血浆睾酮浓度升高时具有攻击性。然而，先前的实验已确定，在繁殖季节，睾酮不会因领地挑战而增加，且睾酮植入物也不会使雄性更具攻击性。睾酮与攻击性之间的这种关系不同于与之亲缘关系较近的北半球物种。我们进行了另一项实验，研究睾酮在繁殖季节对雄性棕颈雀鹀领地攻击性的介导作用。我们预测，阻断睾酮的作用会抑制对领地挑战的攻击性反应。在繁殖季节早期，使用模拟领地入侵捕获雄性，捕获时间与血浆睾酮、二氢睾酮和皮质酮浓度之间没有关系。然后给个体雄性植入芳香化酶抑制剂ATD和抗雄激素氟他胺，或植入空植入物作为对照。一周后，用模拟领地入侵对鸟类进行挑战，并测量其攻击性反应。两组之间在个体行为反应（鸣叫次数、飞行次数、最接近距离或在5米内的时间）或总体攻击性方面没有差异。植入后，实验组的雄激素水平升高，表明该处理通过阻断负反馈系统取得了成功。我们得出结论，在繁殖季节通过药物抑制睾酮不会影响这些鸟类的领地攻击性。
