Data from: Melanin in a changing world: brown trout coloration reflects alternative reproductive strategies in variable environments

Melanins are the most widespread pigments in animals but their adaptive significance remains elusive. Recent studies suggest that intraspecific variation in melanin-based coloration reflects individual genetic-based alternative strategies to cope with environment variability, which could be crucial for their responses to climate changes. However, empirical evidence is still scarce. In this study, we tested how skin coloration in natural populations of brown trout Salmo trutta fario would reflect alternative reproductive strategies in different environments. We experimentally manipulated the flow regime (constant vs. variable) in artificial streams and compared the reproductive investment (body mass and plasma triglyceride variations), innate immunity (variations in plasma peroxidase and lysozyme activity) and reproductive success (number of mates and offspring) of differently colored brown trout over 2 reproductive seasons. Results show that darker males had a higher reproductive investment, but similar immune variations during reproduction compared to paler males. In addition, this reproductive investment was higher in variable environments. However, this did not translate into a higher reproductive success in variable environments, as darker males had a similar number of mates and offspring compared to their paler counterparts under a variable water flow. Since climate change will likely lead to an increased flow variability in the next decades, this suggests that darker brown trout could incur a higher energetic cost of reproduction and could be more impacted by climate changes than their paler counterparts. This highlights the need to take into account intraspecific variability to better forecast the response of natural populations to climate changes.

黑色素（Melanins）是动物界分布最为广泛的色素类群，但其适应意义迄今仍难以阐明。近期研究表明，基于黑色素的体色种内变异，反映了个体应对环境波动的遗传基础适应性策略，这对于种群响应气候变化或具有关键意义。然而，相关实证证据仍较为匮乏。本研究以褐鳟（Salmo trutta fario）的自然种群为研究对象，探究其体色差异如何反映不同环境下的替代性繁殖策略。我们通过人工溪流操控水流模式（恒定vs可变），并比对了两个繁殖季内，不同体色褐鳟的繁殖投入（体质量与血浆甘油三酯水平变化）、先天免疫功能（血浆过氧化物酶与溶菌酶活性变化）以及繁殖成功率（交配对象数量与后代数量）。研究结果显示，相较于体色较浅的雄性个体，体色更深的雄性具有更高的繁殖投入，但二者在繁殖期间的免疫变化水平并无显著差异。此外，可变水流环境下的个体繁殖投入显著更高。但这并未使可变水流环境下的个体获得更高的繁殖成功率：在可变水流条件下，体色更深的雄性与体色较浅的同类相比，其交配对象数量与后代数量并无显著差异。鉴于未来数十年间气候变化或会导致水流变异性显著升高，本研究结果提示，体色更深的褐鳟可能需要承担更高的繁殖能量成本，且相较于体色较浅的同类，其更容易受到气候变化的负面影响。本研究凸显了纳入种内变异维度的必要性，以更精准地预测自然种群对气候变化的响应。