Background The geometric patterns that adorn the shells of many phylogenetically disparate molluscan species are comprised of pigments that span the visible spectrum. Although early chemical studies implicated melanin as a commonly employed pigment, surprisingly little evidence generated with more recent and sensitive techniques exists to support these observations. Results Here we present the first mass spectrometric investigations for the presence of eumelanin and pheomelanin in 13 different molluscan species from three conchiferan classes: Bivalvia, Cephalopoda and Gastropoda. In the bivalve Mytilus edulis we demonstrate that eumelanin mainly occurs in the outermost, non-mineralised and highly pigmented layer of the shell (often referred to as the periostracum). We also identified eumelanin in the shells of the cephalopod Nautilus pompilius and the marine gastropods Clanculus pharaonius and Steromphala adriatica. In the terrestrial gastropod Cepaea nemoralis we verify the presence of pheomelanin in a mollusc shell for the first time. Surprisingly, in a large number of brown/black coloured shells we did not find any evidence for either type of melanin. Conclusions We recommend methods such as high-performance liquid chromatography with mass spectrometric detection for the analysis of complex biological samples to avoid potential false-positive identification of melanin. Our results imply that many molluscan species employ as yet unidentified pigments to pattern their shells. This has implications for our understanding of how molluscs evolved the ability to pigment and pattern their shells, and for the identification of the molecular mechanisms that regulate these processes.

中文翻译：

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软体动物壳中的真黑素和褐黑素色素沉着可能不如预期常见：来自质谱的见解。


背景 许多系统发育不同的软体动物物种的贝壳上装饰的几何图案由跨越可见光谱的颜料组成。尽管早期的化学研究表明黑色素是一种常用的色素，但令人惊讶的是，用更现代和更敏感的技术产生的证据很少支持这些观察结果。结果在这里，我们首次对来自三个贝类（双壳类、头足类和腹足类）的 13 种不同软体动物物种中真黑素和褐黑素的存在进行了质谱研究。在双壳贝类贻贝中，我们证明真黑素主要存在于壳的最外层、非矿化且高度色素化的层（通常称为骨膜）中。我们还在头足类动物 Nautilus pompilius 和海洋腹足类动物 Clanculus pharaonius 和 Steromphala adriatica 的壳中发现了真黑色素。在陆生腹足动物 Cepaea nemoralis 中，我们首次证实软体动物壳中存在褐黑素。令人惊讶的是，在大量棕色/黑色贝壳中，我们没有发现任何一种黑色素的证据。结论 我们推荐使用高效液相色谱结合质谱检测等方法来分析复杂的生物样品，以避免潜在的黑色素假阳性鉴定。我们的结果表明，许多软体动物物种使用尚未识别的颜料来装饰它们的贝壳。这对于我们理解软体动物如何进化出给贝壳着色和形成图案的能力以及识别调节这些过程的分子机制具有重要意义。