George Elizabeth M, Wolf Sarah E, Bentz Alexandra B, Rosvall Kimberly A
Department of Biology, Indiana University Bloomington, Bloomington, IN, USA.
Behav Ecol. 2021 Nov 14;33(1):233-244. doi: 10.1093/beheco/arab129. eCollection 2022 Jan-Feb.
Competitive interactions often occur in series; therefore animals may respond to social challenges in ways that prepare them for success in future conflict. Changes in the production of the steroid hormone testosterone (T) are thought to mediate phenotypic responses to competition, but research over the past few decades has yielded mixed results, leading to several potential explanations as to why T does not always elevate following a social challenge. Here, we measured T levels in tree swallows (), a system in which females compete for limited nesting cavities and female aggression is at least partially mediated by T. We experimentally induced social challenges in two ways: (1) using decoys to simulate territorial intrusions and (2) removing subsets of nesting cavities to increase competition among displaced and territory-holding females. Critically, these experiments occurred pre-laying, when females are physiologically capable of rapidly increasing circulating T levels. However, despite marked aggression in both experiments, T did elevate following real or simulated social challenges, and in some cases, socially challenged females had lower T levels than controls. Likewise, the degree of aggression was negatively correlated with T levels following a simulated territorial intrusion. Though not in line with the idea that social challenges prompt T elevation in preparation for future challenges, these patterns nevertheless connect T to territorial aggression in females. Coupled with past work showing that T promotes aggression, these results suggest that T may act rapidly to allow animals to adaptively respond to the urgent demands of a competitive event.
竞争性互动通常是一连串发生的；因此，动物可能会以某种方式应对社会挑战，使它们为未来冲突中的成功做好准备。类固醇激素睾酮（T）分泌的变化被认为介导了对竞争的表型反应，但过去几十年的研究结果喜忧参半，这引发了几种关于为何T在社会挑战后并非总是升高的潜在解释。在这里，我们测量了树燕（）的T水平，在这个系统中，雌性争夺有限的筑巢洞穴，并且雌性的攻击性至少部分由T介导。我们通过两种方式实验性地引发社会挑战：（1）使用诱饵模拟领地入侵，（2）移除部分筑巢洞穴以增加被驱赶雌性和拥有领地雌性之间的竞争。关键的是，这些实验在产卵前进行，此时雌性在生理上有能力迅速提高循环T水平。然而，尽管在两个实验中都出现了明显的攻击性，但T在真实或模拟的社会挑战后并未升高，而且在某些情况下，受到社会挑战的雌性T水平低于对照组。同样，在模拟领地入侵后，攻击性程度与T水平呈负相关。尽管这与社会挑战促使T升高以应对未来挑战的观点不一致，但这些模式仍然将T与雌性的领地攻击性联系起来。再加上过去的研究表明T会促进攻击性，这些结果表明T可能会迅速发挥作用，使动物能够对竞争事件的紧迫需求做出适应性反应。
