In cooperatively breeding cichlid fish, the early social environment has lifelong effects on the offspring's behaviour, life-history trajectories and brain gene expression. Here, we asked whether the presence or absence of parents and subordinate helpers during early life also shapes fluctuating levels of cortisol, the major stress hormone in the cichlid Neolamprologus pulcher. To non-invasively characterize baseline and stress-induced cortisol levels, we adapted the ‘static’ holding-water method often used to collect waterborne steroid hormones in aquatic organisms by including a flow-through system allowing for repeated sampling without handling of the experimental subjects. We used 8-year-old N. pulcher either raised with (+F) or without (−F) parents and helpers in early life. We found that N. pulcher have a peak of their circadian cortisol cycle in the early morning, and that they habituated to the experimental procedure after four days. Therefore, we sampled the experimental fish in the afternoon after four days of habituation. −F fish had significantly lower baseline cortisol levels, whereas stress-induced cortisol levels did not differ between treatments. Thus, we show that the early social environment has life-long effects on aspects of the physiological stress system of the Hypothalamic-Pituitary-Interrenal (HPI) axis. We discuss how these differences in physiological state may have contributed to the specialization in different social and life-history trajectories of this species.

在合作养殖慈鲷鱼中，早期的社会环境对后代的行为、生活史轨迹和大脑基因表达具有终身影响。在这里，我们询问了在生命早期是否存在父母和下属助手是否也会影响皮质醇水平的波动，皮质醇是慈鲷Neolamprologus pulcher的主要压力激素。为了非侵入性地表征基线和压力诱导的皮质醇水平，我们采用了“静态”保持水方法，该方法通常用于收集水生生物中的水性类固醇激素，包括一个流通系统，允许在不处理实验对象的情况下重复采样. 我们使用了 8 岁的N. pulcher在早期生活中与（+F）或没有（-F）父母和助手一起长大。我们发现N. pulcher在清晨的皮质醇昼夜节律周期达到峰值，并且在四天后它们习惯了实验程序。因此，我们在适应四天后的下午对实验鱼进行了采样。-F 鱼的基线皮质醇水平显着降低，而应激诱导的皮质醇水平在治疗之间没有差异。因此，我们表明早期社会环境对下丘脑-垂体-肾间 (HPI) 轴的生理应激系统的各个方面具有终生影响。我们讨论了这些生理状态的差异如何促成了该物种在不同社会和生活史轨迹上的专业化。