Department of Biology and Graduate Degree Program in Ecology, Colorado State University, Fort Collins, CO 80523, USA.
Department of Biology, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.
Integr Comp Biol. 2020 Aug 1;60(2):332-347. doi: 10.1093/icb/icaa056.
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 toward 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.
权衡的概念贯穿于我们对适应性进化的思考之中，因为它们在生物组织的各个层次都有体现，从分子和细胞过程到生物体和生态功能。权衡不可避免地出现，因为不同的特征不是孤立存在的，而是嵌入在构成整个生物体的复杂、综合的系统中。权衡的遗传和机械基础可以在特征之间共享的生物途径中的多效性节点中找到。然而，权衡通常仅被理解为统计相关性，限制了评估选择和约束在适应性进化过程中相互作用的能力。在这里，我们首先回顾了生理学家和进化生物学家研究权衡的经典范式，并强调了网络和分子途径方法如何将这些范式统一起来。我们讨论了这些方法如何使研究人员能够评估为什么会出现权衡，以及选择如何克服特征相关性和进化约束。我们认为，理解不同特征和功能之间保守的分子途径是如何共享的，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，使他们能够朝着理解特征相关性和权衡出现的原因的目标进行有意义的合作。我们简要地强调了黑素皮质素系统和激素对渗透压调节的控制，作为两个案例研究，理解共享的分子途径揭示了为什么在看似不相关的特征之间会出现权衡。虽然我们认识到应用这些方法特别是在自然种群的背景下存在挑战和限制，但我们主张关注导致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。
