Department of Earth and Environmental Sciences, Paleontology and Geobiology, Ludwig-Maximilians-Universität, Munich, Germany.
Department of Earth and Environmental Sciences, Crystallography, Ludwig-Maximilians-Universität, Munich, Germany.
Geobiology. 2024 Jan-Feb;22(1):e12586. doi: 10.1111/gbi.12586.
The formation of skeletal structures composed of different calcium carbonate polymorphs (e.g. aragonite and calcite) appears to be both biologically and environmentally regulated. Among environmental factors influencing aragonite and calcite precipitation, changes in seawater conditions-primarily in the molar ratio of magnesium and calcium during so-called 'Calcite' (mMg:mCa below 2) or 'Aragonite' seas (mMg:mCa above 2)-have had profound impacts on the distribution and performance of marine calcifiers throughout Earth's history. Nonetheless, the fossil record shows that some species appear to have counteracted such changes and kept their skeleton polymorph unaltered. Here, the aragonitic octocoral Heliopora coerulea and the aragonitic scleractinian Montipora digitata were exposed to Calcite Sea-like mMg:mCa with various levels of magnesium and calcium concentration, and changes in both the mineralogy (i.e. CaCO polymorph) and gene expression were monitored. Both species maintained aragonite deposition at lower mMg:mCa ratios, while concurrent calcite presence was only detected in M. digitata. Despite a strong variability between independent experimental replicates for both species, the expression for a set of putative calcification-related genes, including known components of the M. digitata skeleton organic matrix (SkOM), was found to consistently change at lower mMg:mCa. These results support the previously proposed involvements of the SkOM in counteracting decreases in seawater mMg:mCa. Although no consistent expression changes in calcium and magnesium transporters were observed, down-regulation calcium channels in H. coerulea in one experimental replicate and at an mMg:mCa of 2.5, pointing to a possible active calcium uptake regulation by the corals under altered mMg:mCa.
不同碳酸钙多晶型体（例如文石和方解石）组成的骨骼结构的形成似乎受到生物和环境的调节。在影响文石和方解石沉淀的环境因素中，海水条件的变化——主要是在所谓的“方解石”（mMg:mCa 低于 2）或“文石”海（mMg:mCa 高于 2）期间镁和钙的摩尔比——对地球历史上海洋钙化生物的分布和性能产生了深远的影响。尽管如此，化石记录表明，有些物种似乎已经抵消了这些变化，并保持其骨骼多晶型不变。在这里，文石八放珊瑚 Heliopora coerulea 和文石珊瑚 Montipora digitata 暴露在类似方解石海的 mMg:mCa 中，其中镁和钙的浓度不同，并监测了矿物学（即 CaCO 多晶型）和基因表达的变化。这两个物种在较低的 mMg:mCa 比值下保持文石沉积，而同时仅在 M. digitata 中检测到方解石存在。尽管这两个物种的独立实验重复之间存在很强的可变性，但一组假定的钙化相关基因的表达，包括 M. digitata 骨骼有机基质（SkOM）的已知成分，被发现始终在较低的 mMg:mCa 下发生变化。这些结果支持了 SkOM 参与抵消海水 mMg:mCa 降低的先前提出的假设。尽管没有观察到钙和镁转运蛋白的一致表达变化，但在一个实验重复中，H. coerulea 中的钙通道下调，在 mMg:mCa 为 2.5 时，表明珊瑚在改变的 mMg:mCa 下可能通过主动的钙摄取调节。
