Composition Systematics in the Exoskeleton of the American Lobster, Homarus americanus and Implications for Malacostraca
Composition Systematics in the Exoskeleton of the American Lobster, Homarus americanus and Implications for Malacostraca
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DOI：
10.3389/feart.2019.00069
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发表时间：
2019-04-05
影响因子：
2.9
通讯作者：
Dove, Patricia M.
中科院分区：
文献类型：
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作者：
Mergelsberg, Sebastian T.;Ulrich, Robert N.;Dove, Patricia M.
对龙虾和其他甲壳类动物外骨骼生物矿物的研究报告称，不同身体部位的化学异质性阻碍了基于成分的环境代理模型的发展。然而，坊间证据表明，这种生物复合材料的矿物成分中可能存在潜在的成分系统。我们通过设计一个方案来测试这个想法，分别提取外骨骼的矿物[无定形碳酸钙(ACC) +方解石]和有机（几丁质+蛋白质）部分。用ICP-OES和其他湿化学方法对组分进行分析，定量样品、矿物和有机基质中Mg、Ca和P的含量。将这种方法应用于美洲龙虾（Homarus americanus）的七个身体部位的外骨骼，我们描述了每个部分的化学成分。测量结果证实，龙虾外骨骼中的Mg、P和Ca浓度变化很大。然而，矿物组分中Mg/Ca和P/Ca的比值在所有部分都是恒定的，除了螯合（爪），它们被抵消到更高的值。通过将浓度归一化得到P/Ca和Mg/Ca，我们发现所有身体部位都将P/Mg保持在1.27 +/- 0.30。研究结果表明，龙虾有望成为一种记录CaCO3生物矿物组成系统的新型动物。利用高能x射线衍射和PDF分析，对大量样品进行平行结构分析，证实在每个身体部位的矿物组分中，ACC相对于方解石的比例很大。没有证据表明存在磷酸相。回到其他海洋（螃蟹、龙虾和海洋虾）和陆地（球虫）甲壳类动物的成分报告中，我们发现这些生物中也有类似的Mg/Ca和P/Ca模式的证据。这些关系为开发新的环境重建代理提供了基础，并为如何优化组成以满足外骨骼中矿物部分的功能需求提供了见解。组分的变异性和溶解度的差异表明，在化石记录中观察到的地面学偏差存在热力学基础。
Studies of biominerals from the exoskeletons of lobsters and other crustaceans report chemical heterogeneities across disparate body parts that have prevented the development of composition-based environmental proxy models. Anecdotal evidence, however, suggests underlying composition systematics may exist in the mineral component of this biocomposite material. We test this idea by designing a protocol to separately extract the mineral [amorphous calcium carbonate (ACC) plus calcite] and organic (chitin plus protein) fractions of the exoskeleton. The fractions were analyzed by ICP-OES and other wet chemistry methods to quantify Mg, Ca, and P contents of the bulk, mineral, and organic matrix. Applying this approach to the exoskeleton for seven body parts of the American lobster, Homarus americanus, we characterize the chemical composition of each fraction. The measurements confirm that Mg, P, and Ca concentrations in lobster exoskeletons are highly variable. However, the ratios of Mg/Ca and P/Ca in the mineral fraction are constant for all parts, except the chelae (claws), which are offset to higher values. By normalizing concentrations to obtain P/Ca and Mg/Ca, we show that all body parts conserve P/Mg to 1.27 +/- 0.30. The findings suggest lobsters hold promise as a novel class of animals that record composition systematics within their CaCO3 biominerals. Parallel structural analyses of the bulk samples confirm a large proportion of ACC relative to calcite in the mineral fractions for each body part using high-energy X-ray diffraction and PDF analysis. There is no evidence for a phosphate phase. Returning to compositions reported for other marine (crab, lobster, and marine shrimp) and terrestrial (pillbug) crustaceans, we find evidence for similar Mg/Ca and P/Ca patterns in these organisms. The relationships provide a basis for developing new proxies for environmental reconstructions using animals from the class Malacostraca and provide insights into how composition may be optimized to meet functional requirements of the mineral fraction in exoskeletons. Compositional variability, and hence differential solubility, suggests a thermodynamic basis for the taphonomic bias that is observed in the fossil record.