The evolution and maintenance of color clines is a classic topic of research in evolutionary ecology. However, studies analyzing the temporal dynamics of such clines are much less frequent, due to the difficulty of obtaining reliable data about past color distributions along environmental gradients. In this paper, we describe a case of decades-long temporal stability and directional change in a color cline of the marine snail Littorina saxatilis along the coastal inlet of the Ría de Vigo (NW Spain). L. saxatilis from this area shows a clear color cline with three distinct areas from the innermost to the more wave exposed localities of the Ría: the inner, protected localities show an abundance of fawn-like individuals; the intermediate localities show a high diversity of colors; and the outer, wave exposed localities show populations with a high frequency of a black and lineated morph. We compare data from the 1970s and 2022 in the same localities, showing that the cline has kept relatively stable for at least over half a century, except for some directional change and local variability in the frequency of certain morphs. Multiple regression analyses and biodiversity measures are presented to provide clues into the selective pressures that might be involved in the maintenance of this color cline. Future research avenues to properly test the explanatory power of these selective agents as well as the possible origins of the cline are discussed.

中文翻译：

---

西班牙西北部海蜗牛色系的时间稳定性和方向变化

有色系的进化和维持是进化生态学研究的经典课题。然而，由于难以获得有关沿环境梯度的过去颜色分布的可靠数据，分析此类克隆的时间动态的研究要少得多。在本文中，我们描述了沿 Ría de Vigo（西班牙西北部）沿海入口的海洋蜗牛 Littorina saxatilis 的颜色斜坡长达数十年的时间稳定性和方向变化的案例。来自该区域的 L. saxatilis 显示出清晰的颜色斜坡，具有三个不同的区域，从最里面到 Ría 的波浪暴露更多的地方：内部受保护的地方显示出大量的小鹿样个体；中间地区显示出高度多样化的颜色；和外面，暴露在波浪中的地方显示出具有高频率黑色和线状变形的种群。我们比较了同一地区 1970 年代和 2022 年的数据，表明该斜坡至少在半个多世纪内保持相对稳定，除了一些方向变化和某些变形频率的局部变化。提出了多元回归分析和生物多样性措施，以提供有关可能参与维持这种有色系的选择压力的线索。讨论了正确测试这些选择剂的解释力以及 cline 的可能起源的未来研究途径。除了某些变形频率的一些方向变化和局部变化之外。提出了多元回归分析和生物多样性措施，以提供有关可能参与维持这种有色系的选择压力的线索。讨论了正确测试这些选择剂的解释力以及 cline 的可能起源的未来研究途径。除了某些变形频率的一些方向变化和局部变化之外。提出了多元回归分析和生物多样性措施，以提供有关可能参与维持这种有色系的选择压力的线索。讨论了正确测试这些选择剂的解释力以及 cline 的可能起源的未来研究途径。