George Elizabeth M, Rosvall Kimberly A
Department of Biology, Indiana University, Bloomington, IN 47405.
Center for the Integrated Study of Animal Behavior, Indiana University, Bloomington, IN 47405.
Integr Comp Biol. 2022 Jun 27;62(3):474-86. doi: 10.1093/icb/icac100.
Experimentally elevated testosterone (T) often leads to enhanced aggression, with examples across many different species, including both males and females. Indeed, the relationship between T and aggression is among the most well-studied and fruitful areas of research at the intersection of behavioral ecology and endocrinology. This relationship is also hypothesized to be bidirectional (i.e., T influences aggression, and aggression influences T), leading to four key predictions: (1) Individuals with higher T levels are more aggressive than individuals with lower T. (2) Seasonal changes in aggression mirror seasonal changes in T secretion. (3) Aggressive territorial interactions stimulate increased T secretion. (4) Temporary elevations in T temporarily increase aggressiveness. These predictions cover a range of timescales, from a single snapshot in time, to rapid fluctuations, and to changes over seasonal timescales. Adding further complexity, most predictions can also be addressed by comparing among individuals or with repeated sampling within-individuals. In our review, we explore how the spectrum of results across predictions shapes our understanding of the relationship between T and aggression. In all cases, we can find examples of results that do not support the initial predictions. In particular, we find that predictions 1-3 have been tested frequently, especially using an among-individual approach. We find qualitative support for all three predictions, though there are also many studies that do not support predictions 1 and 3 in particular. Prediction 4, on the other hand, is something that we identify as a core underlying assumption of past work on the topic, but one that has rarely been directly tested. We propose that when relationships between T and aggression are individual-specific or condition-dependent, then positive correlations between the two variables may be obscured or reversed. In essence, even though T can influence aggression, many assumed or predicted relationships between the two variables may not manifest. Moving forward, we urge greater attention to understanding how and why it is that these bidirectional relationships between T and aggression may vary among timescales and among individuals. In doing so, we will move towards a deeper understanding on the role of hormones in behavioral adaptation.
实验性地提高睾酮（T）水平通常会导致攻击性增强，在许多不同物种中都有实例，包括雄性和雌性。事实上，T与攻击性之间的关系是行为生态学和内分泌学交叉领域中研究最充分且成果丰硕的研究领域之一。这种关系也被假设为双向的（即，T影响攻击性，攻击性也影响T），从而产生了四个关键预测：（1）T水平较高的个体比T水平较低的个体更具攻击性。（2）攻击性的季节性变化反映T分泌的季节性变化。（3）攻击性的领地互动会刺激T分泌增加。（4）T的暂时升高会暂时增加攻击性。这些预测涵盖了一系列时间尺度，从单个时间点的快照，到快速波动，再到季节性时间尺度上的变化。更复杂的是，大多数预测也可以通过个体间比较或个体内重复抽样来进行研究。在我们的综述中，我们探讨了各个预测结果的范围如何塑造我们对T与攻击性之间关系的理解。在所有情况下，我们都能找到不支持初始预测的结果实例。特别是，我们发现预测1 - 3已经被频繁测试，尤其是采用个体间方法。我们发现对所有这三个预测都有定性支持，不过也有许多研究尤其不支持预测1和3。另一方面，预测4是我们确定为该主题过去研究的一个核心潜在假设，但很少被直接测试。我们提出，当T与攻击性之间的关系是个体特异性或条件依赖性时，那么这两个变量之间的正相关可能会被掩盖或逆转。本质上，即使T可以影响攻击性，这两个变量之间许多假定或预测的关系可能并不会显现出来。展望未来，我们敦促更加关注理解T与攻击性之间的这些双向关系如何以及为何会在时间尺度和个体之间有所不同。这样做，我们将朝着更深入理解激素在行为适应中的作用迈进。
