Data from: Conflict between background matching and social signalling in a colour-changing freshwater fish

The ability to change coloration allows animals to modify their patterning to suit a specific function. Many freshwater fishes, for example, can appear cryptic by altering the dispersion of melanin pigment in the skin to match the visual background. However, melanin-based pigments are also used to signal dominance among competing males; thus colour change for background matching may conflict with colour change for social status signalling. We used a colour-changing freshwater fish to investigate whether colour change for background matching influenced aggressive interactions between rival males. Subordinate males that had recently darkened their skin for background matching received heightened aggression from dominant males, relative to males whose coloration had not changed. We then determined whether the social status of a rival male, the focal male's previous social status, and his previous skin coloration, affected a male's ability to change colour for background matching. Social status influenced skin darkening in the first social encounter, with dominant males darkening more than subordinate males, but there was no effect of social status on colour change in the second social encounter. We also found that the extent of skin colour change (by both dominant and subordinate males) was dependent on previous skin coloration, with dark males displaying a smaller change in coloration than pale males. Our findings suggest that skin darkening for background matching imposes a significant social cost on subordinate males in terms of increased aggression. We also suggest that the use of melanin-based signals during social encounters can impede subsequent changes in skin coloration for other functions, such as skin darkening for background matching.

体色变色能力可让动物调整自身的体表图案，以适配特定功能需求。例如，诸多淡水鱼类可通过改变皮肤内黑色素的分布，使其体色匹配视觉背景，从而呈现隐蔽状态。然而，黑色素类色素也可在竞争的雄性个体间用于传递优势地位信号，因此为背景匹配而进行的体色变化，与为社会地位信号传递而进行的体色变化可能存在冲突。本研究以一种具备变色能力的淡水鱼类为实验对象，探究为背景匹配而发生的体色变化是否会影响竞争雄性间的攻击互动。相较于体色未发生变化的雄性个体，近期为背景匹配而使皮肤黑化的从属雄性，会受到优势雄性更强烈的攻击行为。随后，我们进一步明确了竞争雄性的社会地位、目标雄性既往的社会地位，以及其先前的皮肤体色，是否会影响雄性为背景匹配而进行体色变化的能力。在首次社交互动中，社会地位会影响皮肤黑化程度：优势雄性的体色加深幅度大于从属雄性；但在第二次社交互动中，社会地位对体色变化并无显著影响。我们还发现，（优势与从属雄性的）皮肤体色变化幅度均与其先前的皮肤体色相关：深色雄性的体色变化幅度小于浅色雄性。本研究结果表明，为背景匹配而进行的皮肤黑化，会让从属雄性面临显著的社会成本，具体表现为其所受攻击行为增加。此外，本研究还提出，社交互动中使用黑色素类信号，可能会阻碍后续为其他功能进行的皮肤体色变化——例如为背景匹配而进行的皮肤黑化。