Season of birth affects social behaviours and stress physiology differently in males and females of the wild cavy (Cavia aperea)

Behavioural, physiological, and life-history traits are often shaped by the environment. The pace-of-life syndrome (POLS) hypothesis suggests that environmental differences affect individuals consistently, i.e. shaping personality traits. Recently, the original POLS concept has been refined to incorporate predictable differences between sexes. Here, we test POLS predictions regarding aggressiveness, affiliative interactions and their relationship with fearlessness, boldness and blood cortisol concentrations in a precocial rodent. We induced differences in pace-of-life by dynamically changing photoperiod (simulating spring or autumn). We measured boldness, fearlessness, social behaviours and baseline cortisol concentrations in both sexes. In addition, females were tested in a group integration situation. We show that affiliative and aggressive interactions in a social encounter test represent consistent (i.e. personality) traits. In accordance with POLS predictions, social behaviours differed between animals born in different seasons, facing predictably different life histories under natural conditions, albeit in a sex-specific way. Autumn-born males were less aggressive while autumn-born females were more aggressive. While there was no seasonal difference in baseline or stress-induced cortisol concentrations during integration into groups of unfamiliar females, spring-born females lost more body mass, indicating higher levels of stress. The non-social personality traits predicted aggressive behaviour in social situations, again, in a sex-specific way. While bold males showed more interactions in general and more aggressive interactions, boldness did not affect reactions of females. Fearless males and females initiated more aggressive interactions. Taken together, these results indicate that social personality traits interact with non-social personality traits in a complex, sex-specific way, leading to sex-specific syndromes.

行为、生理及生命史特征常受环境塑造。生活节奏综合征（POLS）假说提出，环境差异对个体产生持续影响，即塑造个性特征。近期，POLS概念的原始定义已被细化，以纳入性别间的可预测差异。在本研究中，我们检验了POLS关于攻击性、亲和性互动及其与无畏、勇敢及血液皮质醇浓度关系的预测。通过动态改变光周期（模拟春季或秋季）来诱导生活节奏的差异。我们测量了两种性别中的勇敢、无畏、社会行为及基线皮质醇浓度。此外，对雌性进行了群体融合情况的测试。我们发现，在社会遭遇测试中的亲和性和攻击性互动代表了稳定的（即个性）特征。与POLS预测一致，不同季节出生的动物在社会行为上存在差异，在自然条件下面临可预测的不同生命历史，尽管这种差异具有性别特异性。秋季出生的雄性攻击性较低，而秋季出生的雌性攻击性较高。在融入陌生雌性群体时，无论是基线皮质醇浓度还是应激诱导的皮质醇浓度均未出现季节性差异，但春季出生的雌性体重减轻更多，表明其压力水平更高。非社会个性特征预测了社交情境中的攻击性行为，同样地，这种预测也具有性别特异性。勇敢的雄性在总体互动中及更具攻击性的互动中表现更积极，但勇敢程度并不影响雌性的反应。无畏的雄性和雌性更倾向于发起攻击性互动。综合这些结果，表明社会个性特征与非社会个性特征以复杂、性别特异的方式相互作用，导致性别特异性的综合征。