Evolutionary ecology often studies how environmental factors define optimal phenotypes without considering the bodily mechanisms involved in their regulation. Here we used a dynamic optimisation model to investigate optimally concerted hormonal control of the phenotype. We studied a semi‐realistic situation where hormonal control of appetite, metabolism and growth acts to prepare juvenile fish for an uncertain future with regard to food availability. We found a bottom–up effect in that hormone levels varied across environments and affected a range of phenotypic changes. We also describe a top–down effect as natural selection varied across environments, which affected evolutionary optimisation of hormone levels. These combined top–down and bottom–up effects produced a hormone‐regulated phenotype that adjusted its foraging intensity and risk‐taking in adaptive ways depending on the differences between current and expected long‐term environmental conditions. Hence, understanding the response of these fish to their current conditions also requires an understanding of their future expectations. We found that when food availability was low, it was optimal for the juvenile fish to have low growth hormone, thyroid hormone and orexin levels, contrary to when food availability was high when these levels were higher. Individual variation emerged from the individually experienced food availability trajectories: Those that on average experienced higher food availability grew faster and had higher short‐term mortality risk. They also had higher survival probability throughout the growth period. The opposite was true for individuals experiencing lower food availability. Hormonal mechanisms that often are overlooked by ecologists are thus important in the ultimate adaptive control of both behaviour and physiology, thereby impacting fitness through growth and survival.

中文翻译：

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激素对未来期望值的调整影响幼鱼的生长和生存

进化生态学经常研究环境因素如何定义最佳表型，而不考虑其调控所涉及的身体机制。在这里，我们使用动态优化模型来研究表型的最佳协调激素控制。我们研究了一种半现实的情况，其中荷尔蒙控制食欲，新陈代谢和生长起到了使幼鱼准备在食物供应方面不确定的未来的作用。我们发现自下而上的影响在于激素水平随环境的变化而变化，并影响了一系列表型变化。我们还描述了自上而下的效果，因为自然选择随环境的变化而变化，这影响了激素水平的进化优化。这些自上而下和自下而上的综合作用产生了激素调节的表型，根据当前和预期的长期环境条件之间的差异，以适应性方式调整了其觅食强度和冒险行为。因此，了解这些鱼对当前状况的反应还需要了解它们的未来期望。我们发现，当食物供应量较低时，最佳的是使幼鱼的生长激素，甲状腺激素和食欲素水平较低，而当这些食物供应量较高时，其生长激素，甲状腺激素和食欲素水平较低。个体差异从个体经历的食物可获得性轨迹中得出：平均而言，食物可获得性较高的个体增长更快，短期死亡率更高。他们在整个生长期也有较高的生存概率。相反，对于那些食物供应量较低的人来说，情况恰恰相反。因此，生态学家经常忽略的激素机制对于行为和生理的最终自适应控制很重要，从而通过生长和生存影响健康。