The evolution of local adaptation is crucial for the in situ persistence of populations in changing environments. However, selection along broad environmental gradients could render local adaptation difficult, and might even result in maladaptation. We address this issue by quantifying fitness trade-offs (via common garden experiments) along a salinity gradient in two populations of the Neotropical water strider Telmatometra withei—a species found in both fresh (FW) and brackish (BW) water environments across Panama. We found evidence for local adaptation in the FW population in its home FW environment. However, the BW population showed only partial adaptation to the BW environment, with a high magnitude of maladaptation along naturally occurring salinity gradients. Indeed, its overall fitness was ~60% lower than that of the ancestral FW population in its home environment, highlighting the role of phenotypic plasticity, rather than local adaptation, in high salinity environments. This suggests that populations seemingly persisting in high salinity environments might in fact be maladapted, following drastic changes in salinity. Thus, variable selection imposed by salinization could result in evolutionary mismatch, where the fitness of a population is displaced from its optimal environment. Understanding the fitness consequences of persisting in fluctuating salinity environments is crucial to predict the persistence of populations facing increasing salinization. It will also help develop evolutionarily informed management strategies in the context of global change.

中文翻译：

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新热带水黾沿盐度梯度的进化失配

局部适应的进化对于种群在不断变化的环境中的原地持久存在至关重要。然而，沿着广泛的环境梯度进行选择可能会使局部适应变得困难，甚至可能导致适应不良。我们通过量化新热带水黾Telmatometra withei两个种群的适应度权衡（通过常见的花园实验）来解决这个问题（通过常见的花园实验），Telmatometra withei 是巴拿马淡水 (FW) 和咸水 (BW) 水环境中发现的物种。我们发现了 FW 种群在其家乡 FW 环境中进行局部适应的证据。然而，BW种群仅表现出对BW环境的部分适应，并且沿着自然发生的盐度梯度存在高度适应不良。事实上，它的整体适应性比其家乡环境中的祖先 FW 种群低约 60%，这凸显了高盐度环境中表型可塑性的作用，而不是局部适应的作用。这表明，在盐度发生剧烈变化后，看似持续生活在高盐度环境中的种群实际上可能会出现适应不良。因此，盐碱化带来的变量选择可能会导致进化失配，使种群的适应度偏离其最佳环境。了解盐度波动环境中持续存在的适应性后果对于预测面临日益盐化的种群的持续存在至关重要。它还将有助于在全球变化的背景下制定进化信息管理策略。