Data from: Camouflaged or tanned: plasticity in freshwater snail pigmentation

By having phenotypically plastic traits, such as morphology, behaviour and life history, many organisms optimise their fitness in response to fluctuating threats. Freshwater snails with translucent shells, e.g. snails from the Radix genus, differ considerably in their mantle pigmentation patterns, with snails from the same water body ranging from completely dark pigmented to only a few dark patterns. These pigmentation differences have previously been suggested to be genetically fixed, but we suggest that this polymorphism is due to phenotypic plasticity in response to a fluctuating environment. Hence, we here aimed at assessing if common stressors, including ultraviolet radiation (UVR) and predation, induce a plastic response in mantle pigmentation patterns of Radix balthica. We show, in contrast to previous studies, that snails are plastic in their expression of mantle pigmentation in response to changes in UVR and predator threats, i.e. differences among species or populations are not genetically fixed. When exposed to cues from visually hunting fish, R. balthica increased the proportion of their dark pigmentation, suggesting a crypsis strategy. Snails increased their pigmentation even further in response to UVR, but this also lead to reduced complexity of the patterns. Furthermore, when exposed to UVR and fish, snails responded in the same way as in the UVR treatment, suggesting a trade-off between photoprotection and crypsis.

许多生物可借助表型可塑性性状（包括形态、行为与生活史特征），针对波动的生存威胁优化自身适合度。半透明壳的淡水螺（如萝卜螺属（Radix）螺类）的外套膜色素沉着模式差异显著，同一水域内的个体可呈现从完全深色沉着到仅存少量深色纹路的连续分布。此前这类色素沉着差异被认为是遗传固定的，但本研究提出，该多态性实则源于针对波动环境的表型可塑性。因此本研究旨在探究两类常见胁迫因子——紫外线辐射（ultraviolet radiation, UVR）与捕食作用——是否会诱导巴氏萝卜螺（Radix balthica）的外套膜色素沉着模式产生可塑性响应。与既往研究结论相悖，本研究证实螺类的外套膜色素沉着表达可响应紫外线辐射与捕食者威胁的变化而呈现可塑性，即物种或种群间的色素差异并非遗传固定的。当暴露于视觉捕食鱼类的化学信号时，巴氏萝卜螺会提升其深色色素沉着的占比，提示其采取了隐蔽策略。而当单独暴露于紫外线辐射时，螺类的色素沉着程度进一步升高，但这同时会导致色素纹路的复杂度下降。此外，当同时暴露于紫外线辐射与鱼类捕食信号时，螺类的响应与单独紫外线辐射处理组一致，这表明光保护与隐蔽策略之间存在权衡。