Bidirectional relationships between testosterone and aggression: a critical analysis of four predictions

How a territorial challenge changes sex steroid-related gene networks in the female brain: A field experiment with the tree swallow

Territorial competition can stimulate secretion of testosterone (T), which is thought to act on neural circuits of aggression to promote further aggression. Here, we test the hypothesis that competition modulates sex steroid sensitivity and conversion in the brain, focused on the female tree swallow (Tachycineta bicolor). In this bird species, exogenous T enhances female aggression, but social competition for limited nesting territories does not stimulate systemic T elevation. We exposed free-living females to simulated territorial intrusions and sampled five regions of the vertebrate social behavior network (SBN). Using quantitative PCR, we measured mRNA abundance of: androgen receptor, 5-alpha reductase, estrogen receptor alpha, and aromatase. Using standard analyses, we found essentially no treatment effect on mRNA abundance in any one brain area; however, network analyses revealed marked socially-induced changes in gene co-expression across the SBN. After a territorial challenge, gene expression was more positively correlated with T, and genes specific to the androgen-signaling pathway were also more positively correlated with one another. The challenged brain also exhibited stronger negative correlations among genes in the nucleus taeniae, but stronger positive correlations between the lateral septum and bed nucleus of the stria terminalis. Together, these findings suggest that, in response to female-female territorial challenges, T acts on androgen-mediated circuits of aggression, with some divergence in gene regulation in the nucleus taeniae. The post-transcriptional consequences of these shifts require more research, but their existence underscores insights to be gained from analyzing the neuroendocrine properties of the SBN using network-level perspectives.

The interrelationship between sleep disturbance symptoms and aggression before and after the campus closure of the COVID-19 pandemic: insight from a cross-lagged panel network model

Background

The COVID-19 pandemic is detrimental to sleep quality and increases aggression among college students. Nevertheless, relevant studies were rare. Hence, we collected longitudinal data during and post-campus closure in the current study to investigate the relationship between sleep disturbance and aggression.

Methods

Data from 665 college students (59.2% females, Meanage = 19.01, SD age = 1.25) were collected before (wave 1) and after (wave 2) the campus closure of COVID-19. All participants were asked to fill out the Buss-Perry Aggression Questionnaire and the Youth Self-Rating Insomnia Scale. Two symptom networks and a cross-lagged panel network were formed and tested.

Results

Hostility has the highest centrality in the symptom network both in waves 1 and 2, and it bridges sleep disturbance and aggression. "Easily be woken" - "wake up too early" and "wake up with tired" - "function hindrance" are two important symptom associations in networks of waves 1 and 2. All symptoms except "difficulty in falling asleep" and "easily be woken" ameliorated after closure. Moreover, "physical aggression" and "hostility" can trigger other symptoms in wave 2.

Conclusion

As the first study about aggression and sleep disturbance in the background of COVID-19, we provide valuable information about the relationship between sleep disturbance and aggression on the symptom dimension.

Evolutionary endocrinology and the problem of Darwin's tangled bank

Like Darwin's tangled bank of biodiversity, the endocrine mechanisms that give rise to phenotypic diversity also exhibit nearly endless forms. This tangled bank of mechanistic diversity can prove problematic as we seek general principles on the role of endocrine mechanisms in phenotypic evolution. A key unresolved question is therefore: to what degree are specific endocrine mechanisms re-used to bring about replicated phenotypic evolution? Related areas of inquiry are booming in molecular ecology, but behavioral traits are underrepresented in this literature. Here, I leverage the rich comparative tradition in evolutionary endocrinology to evaluate whether and how certain mechanisms may be repeated hotspots of behavioral evolutionary change. At one extreme, mechanisms may be parallel, such that evolution repeatedly uses the same gene or pathway to arrive at multiple independent (or, convergent) origins of a particular behavioral trait. At the other extreme, the building blocks of behavior may be unique, such that outwardly similar phenotypes are generated via lineage-specific mechanisms. This review synthesizes existing case studies, phylogenetic analyses, and experimental evolutionary research on mechanistic parallelism in animal behavior. These examples show that the endocrine building blocks of behavior have some elements of parallelism across replicated evolutionary events. However, support for parallelism is variable among studies, at least some of which relates to the level of complexity at which we consider sameness (i.e. pathway vs. gene level). Moving forward, we need continued experimentation and better testing of neutral models to understand whether, how - and critically, why - mechanism A is used in one lineage and mechanism B is used in another. We also need continued growth of large-scale comparative analyses, especially those that can evaluate which endocrine parameters are more or less likely to undergo parallel evolution alongside specific behavioral traits. These efforts will ultimately deepen understanding of how and why hormone-mediated behaviors are constructed the way that they are.