There is ongoing debate as to whether fish body size will decrease with global warming and how these changes may impact dispersal ability and speciation rate. Theory predicts that, under warmer temperatures, fish grow to a smaller size, undergo a reduction in dispersal ability and increase speciation rates. However, evaluations of such predictions are hampered owing to the lack of empirical data spanning both wide temporal and geographical scales. Here, using phylogenetic methods, we show that smaller clupeiform fish (anchovies and herrings) occurred historically in warmer waters, moved the shortest distances at low speed and displayed the lowest speciation rates. Furthermore, fish moved faster and evolved rapidly under higher rates of temperature change but these historical rates are far lower than current warming rates. Our results predict a future where smaller clupeiform fish that have reduced ability to move will be more prevalent; this, in turn, may reduce future speciation.

关于鱼体大小是否会随着全球变暖而减小以及这些变化如何影响扩散能力和物种形成率的争论一直存在。理论预测，在较温暖的温度下，鱼的体型会变小，分散能力会降低，物种形成率会增加。然而，由于缺乏跨越广泛时间和地理尺度的经验数据，对此类预测的评估受到阻碍。在这里，使用系统发育方法，我们表明较小的鲱鱼（凤尾鱼和鲱鱼）在历史上出现在温暖的水域中，以低速移动的距离最短，并且显示出最低的物种形成率。此外，在较高的温度变化率下，鱼类的移动速度更快，进化速度更快，但这些历史速率远低于当前的变暖速率。我们的研究结果预测，在未来，移动能力降低的小型鲶鱼将更加普遍；反过来，这可能会减少未来的物种形成。