The concept of trade-offs permeates our thinking about adaptive evolution because they are exhibited at every level of biological organization, from molecular and cellular processes to organismal and ecological functions. Trade-offs inevitably arise because different traits do not occur in isolation, but instead are imbedded within complex, integrated systems that make up whole organisms. The genetic and mechanistic underpinning of trade-offs can be found in the pleiotropic nodes that occur in the biological pathways shared between traits. Yet, often trade-offs are only understood as statistical correlations, limiting the ability to evaluate the interplay between how selection and constraint interact during adaptive evolution. Here, we first review the classic paradigms in which physiologists and evolutionary biologists have studied trade-offs and highlight the ways in which network and molecular pathway approaches unify these paradigms. We discuss how these approaches allow researchers to evaluate why trade-offs arise and how selection can act to overcome trait correlations and evolutionary constraints. We argue that understanding how the conserved molecular pathways are shared between different traits and functions provides a conceptual framework for evolutionary biologists, physiologists, and molecular biologists to meaningfully work together towards the goal of understanding why correlations and trade-offs occur between traits. We briefly highlight the melanocortin system and the hormonal control of osmoregulation as two case studies where an understanding of shared molecular pathways reveals why trade-offs occur between seemingly unrelated traits. While we recognize that applying such approaches poses challenges and limitations particularly in the context of natural populations, we advocate for the view that focusing on the biological pathways responsible for trade-offs provides a unified conceptual context accessible to a broad range of integrative biologists.

中文翻译：

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权衡、多向性和共享分子途径：适应约束的统一观点

权衡的概念渗透到我们对适应性进化的思考中，因为它们体现在生物组织的各个层面，从分子和细胞过程到有机体和生态功能。权衡不可避免地出现，因为不同的特征不是孤立出现的，而是嵌入在构成整个生物体的复杂、集成系统中。权衡的遗传和机制基础可以在性状之间共享的生物途径中发生的多效性节点中找到。然而，权衡通常只被理解为统计相关性，限制了评估适应性进化过程中选择和约束如何相互作用之间相互作用的能力。这里，我们首先回顾生理学家和进化生物学家研究权衡的经典范式，并强调网络和分子途径方法统一这些范式的方式。我们讨论这些方法如何让研究人员评估权衡出现的原因以及选择如何克服特征相关性和进化限制。我们认为，了解保守的分子通路如何在不同的性状和功能之间共享，为进化生物学家、生理学家和分子生物学家提供了一个概念框架，以便有意义地共同努力，以实现理解为什么性状之间会发生相关性和权衡的目标。我们简要强调了黑皮质素系统和渗透调节的激素控制，作为两个案例研究，其中对共享分子途径的理解揭示了为什么看似无关的特征之间会发生权衡。虽然我们认识到应用这些方法会带来挑战和限制，特别是在自然种群的背景下，但我们主张关注负责权衡的生物途径提供了一个统一的概念背景，可供广泛的综合生物学家使用。