Almost fifty years ago the advent of assay methods to measure circulating levels of hormones revolutionized endocrinology in relation to investigations of free-living and captive animals. This new field “environmental endocrinology” revealed that endocrine profiles in animals in their natural habitat were not only different from captive animals, but often deviated from predictions. It quickly became apparent that the organization and analysis of data from the field should be sorted by life history stages such as for reproductive processes, migration, molt etc. and spaced in time according to natural duration of those processes. Presentation of data by calendar date alone gives much simpler, even misleading, patterns. Stage-organized analyses revealed species-specific patterns of hormone secretion and dramatic inter-individual differences. The “Challenge Hypothesis” sparked exploration of these results, which diverged from expectations of hormone-behavior interactions. The hypothesis led to specific predictions about how the hypothalamo-pituitary-gonad axis, and particularly circulating patterns of testosterone, might respond to social challenges such as simulated territorial intrusions. Initially, a group of studies on free-living and captive birds played a key role in the formulation of the hypothesis. Over the decades since, the effects of social challenge and environmental context on hormonal responses have been tested in all vertebrate taxa, including humans, as well as in insects. Although it is now clear that the Challenge Hypothesis in its original form is simplistic, field and laboratory tests of the hypothesis have led to other concepts that have become seminal to the development of environmental endocrinology as a field. In this special issue these developments are addressed and examples from many different taxa enrich the emerging concepts, paving the way for investigations using recent technologies for genetic and transcriptome analyses.

大约五十年前，用于测量激素循环水平的测定方法的出现彻底改变了内分泌学，与研究自由活动和圈养动物有关。这个新的领域“环境内分泌学”揭示了自然栖息地动物体内的内分泌特征不仅与圈养动物不同，而且经常偏离预测。很快就很明显，应该根据生活史阶段（例如生殖过程，迁徙，蜕皮等）对实地数据的组织和分析进行分类，并根据这些过程的自然持续时间在时间​​上进行间隔。仅通过日历日期来显示数据就可以提供更为简单，甚至具有误导性的模式。阶段组织的分析揭示了激素分泌的特定物种模式和巨大的个体间差异。“挑战假说”激发了对这些结果的探索，这与荷尔蒙-行为相互作用的预期背道而驰。该假设导致关于下丘脑-垂体-性腺轴，尤其是睾丸激素的循环方式如何可能对社会挑战（如模拟的领土入侵）做出反应的具体预测。最初，有关自由生活和圈养鸟类的一组研究在假设的制定中起着关键作用。从那以后的几十年中，社会挑战和环境背景对激素反应的影响已在包括人和昆虫在内的所有脊椎动物类群中进行了测试。尽管现在很清楚原始形式的挑战假设很简单，假说的现场测试和实验室测试导致了其他概念，这些概念已成为环境内分泌学作为一个领域发展的开端。在本期特刊中，我们探讨了这些发展，许多不同分类单元的实例丰富了新出现的概念，为使用最新技术进行基因和转录组分析的研究铺平了道路。