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）是动物界分布最广泛的色素之一，但其适应性意义至今仍不甚明确。近期研究表明，基于黑色素的体色种内差异，反映了个体为应对环境变异性所采取的遗传层面差异化生存策略，这或许对物种应对气候变化至关重要。然而相关实证证据仍较为匮乏。本研究以褐鳟（Salmo trutta fario）自然种群的体表体色为研究对象，探究其在不同环境中所体现的差异化繁殖策略。我们通过人工溪流实验操控水流制度（恒定与可变两种模式），并在两个繁殖季内，比较了不同体色褐鳟的繁殖投入（体质量与血浆甘油三酯变化）、先天免疫能力（血浆过氧化物酶与溶菌酶活性变化）以及繁殖成功率（配偶数量与后代数量）。实验结果显示，体色更深的雄性个体具有更高的繁殖投入，但在繁殖期间的免疫指标变化与体色较浅的雄性个体并无显著差异。此外，在可变水流环境中，个体的繁殖投入普遍更高。但这一优势并未转化为可变环境中更高的繁殖成功率：在可变水流条件下，体色更深的雄性个体与体色较浅的同类拥有相近的配偶数量与后代数量。鉴于未来数十年间气候变化或会导致水流变异性升高，本研究结果表明，体色更深的褐鳟或将承担更高的繁殖能量成本，且相比体色较浅的同类，其受气候变化的影响可能更为显著。这一发现凸显了考虑种内变异的必要性，以便更精准地预测自然种群对气候变化的响应。