Explaining how populations adapt to environments is among the foremost objectives of evolutionary theory. Over generations, natural selection impels the phenotypic distribution of a population based on individual variation in phenotype and fitness. However, environmental conditions can also shape how individuals develop within their lifetime to influence which phenotypes are expressed in a population. It has been proposed that such environmentally-initiated phenotypic variation - also termed developmental plasticity - may enable adaptive evolution under some scenarios. As dynamic regulators of development and phenotypic expression, hormones are important physiological mediators of developmental plasticity. Patterns of hormone secretion, hormone transport, and the sensitivity of tissues to hormones can each be altered by environmental conditions, and understanding how endocrine regulation shapes phenotypic development in an ecologically-relevant context has much to contribute toward clarifying the role of plasticity in evolutionary adaptation. This article explores how the environmental sensitivity of endocrine regulation may facilitate 'plasticity-first' evolution by generating phenotypic variants that precede adaptation to altered or novel environments. Predictions arising from 'plasticity-first' evolution are examined in the context of thyroid hormone mediation of morphological plasticity in Cyprinodon pupfishes from the Death Valley region of California and Nevada, USA. This clade of extremophile fishes diversified morphologically over the last ~20,000 years, and observations that some populations experienced contemporary phenotypic differentiation under recent habitat change provide evidence that hormone-mediate plasticity preceded genetic assimilation of morphology in one of the region's species: the Devils Hole pupfish, Cyprinodon diabolis. This example illustrates how conceptualizing hormones not only as regulators of homeostasis, but also as developmental intermediaries between environment conditions and phenotypic variation at the individual-, population-, and species-levels can enrich our understanding of endocrine regulation both as a facilitator of phenotypic change under shifting environments, and as important proximate mechanisms that may initiate 'plasticity-first' evolutionary adaptation.

中文翻译：

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激素，发育可塑性和适应性进化：内分泌灵活性作为“可塑性优先”表型差异的催化剂。

解释种群如何适应环境是进化理论的首要目标。经过几代人，自然选择会根据表型和适​​应性的个体差异来促进人口的表型分布。但是，环境条件也会影响个体在其一生中的发育方式，从而影响人群中哪些表型的表达。已经提出，这种环境引发的表型变异-也称为发育可塑性-在某些情况下可以实现适应性进化。作为发育和表型表达的动态调节剂，激素是发育可塑性的重要生理介质。荷尔蒙分泌，荷尔蒙转运和组织对荷尔蒙的敏感性各有不同，可因环境条件而异，以及了解内分泌调节如何在生态相关的背景下影响表型发育，对阐明可塑性在进化适应中的作用有很大帮助。本文探讨了内分泌调节的环境敏感性如何通过在适应变化或新环境之前产生表型变异来促进“可塑性优先”进化。在美国加利福尼亚州和美国内华达州死亡谷地区的犬Cy的甲状腺可塑性中，在甲状腺激素介导的形态可塑性的背景下，对“可塑性优先”演变产生的预测进行了检验。在过去的大约20,000年中，这种嗜极端鱼类进化出形态多样的物种，和观察到一些种群在最近的生境变化下经历了当代的表型分化，这提供了证据表明，在该地区的一种物种：恶魔洞p，拟南芥中，激素介导的可塑性先于形态的遗传同化。这个例子说明了如何将激素概念不仅作为体内稳态的调节剂，而且作为环境条件与个体，人群和物种水平表型变异之间的发育中介，可以丰富我们对内分泌调节的理解，这既是表型变化的促进者在瞬息万变的环境中，并且是可能引发“可塑性优先”的进化适应的重要邻近机制。