Does soil color affect fish evolution? Differences in color change rate between lineages of the sailfin tetra

ABSTRACT Several organisms match their skin color to the prevalent background color, granting crypsis against predators. The rate at which body color changes occur varies among organisms as a result of physiological constraints and adaptation to variation in contrasts between objects and the environmental background. Faster darkening of body color is favored in environments that show higher amounts of contrast between common objects and the prevailing background. Soil types in Amazon forest streams (igarapés) create distinct environments with respect to the amount of contrast, a result of the amount of sand and clay, which offers different contrasts against dead leaves. Here, we investigated differences in the rates of color change among populations of the sailfin tetra (Crenuchus spilurus) that represent lineages that live in regions of different soil types. Populations inserted into blackwaters (sandy soil) showed higher rates of color darkening in response to exposure to a dark environment composed by dead leaves. We propose that natural selection stemming from predation can favor faster color change rate in environments where there is higher variability of contrasts between leaf litter and soil, which is common in most blackwater streams.

摘要 多种生物可通过将体表颜色匹配于所处环境的主流背景色，从而获得隐蔽性以躲避捕食者。不同生物的体色变化速率存在差异，这源于生理限制以及对物体与环境背景间对比度变化的适应程度差异。在常见物体与主导背景间对比度更高的环境中，体色更快变暗的个体更受自然选择青睐。亚马逊森林溪流（igarapés）的土壤类型会塑造出对比度水平各异的生境，该差异由沙粒与黏土的含量比例决定，且不同土壤与枯叶之间的对比度也存在区别。本研究针对栖息于不同土壤类型区域的帆鳍脂鲤（Crenuchus spilurus）种群的体色变化速率差异展开探究。栖息于黑水（沙质土壤）环境的种群，在暴露于由枯叶构成的黑暗环境时，体色变暗的速率更高。我们提出，由捕食压力驱动的自然选择，会在枯落物与土壤对比度变异性更高的环境中（这类环境在多数黑水溪流中较为常见），青睐体色变化速率更快的个体。