Abstract
Corals build the structural foundation of coral reefs, one of the most diverse and productive ecosystems on our planet. Although the process of coral calcification that allows corals to build these immense structures has been extensively investigated, we still know little about the evolutionary processes that allowed the soft-bodied ancestor of corals to become the ecosystem builders they are today. Using a combination of phylogenomics, proteomics, and immunohistochemistry, we show that scleractinian corals likely acquired the ability to calcify sometime between ∼308 and ∼265 Ma through a combination of lineage-specific gene duplications and the co-option of existing genes to the calcification process. Our results suggest that coral calcification did not require extensive evolutionary changes, but rather few coral-specific gene duplications and a series of small, gradual optimizations of ancestral proteins and their co-option to the calcification process.
Highlights
Reef-building corals build the largest living structures in the world that provide a habitat for more than a quarter of all marine animals (Fisher, et al 2015), and are the primary source of livelihood to hundreds of millions of people (Spalding, et al 2017)
Coral calcification evolved sometime between 308 Mya and 265 Mya Based on a phylogenetic analysis using 1421 single copy orthologs and a time calibrated tree, our result suggest that Corallimorpharia evolved as a sister group of Scleractinia after their common divergence from Actiniaria approximately ~506 Mya (±149 Mya, Fig. 1a)
Using the distribution of divergence time estimates based on BEAST and synonymous substitutions per synonymous sites (Ks) across orthologs identified in all six hexacorallian genomes, we further estimate that the split between Scleractinia and Corallimorpharia dates back to ~308 Mya (±78 Mya Figs. 1a, 1b, 1c)
Summary
Reef-building corals build the largest living structures in the world that provide a habitat for more than a quarter of all marine animals (Fisher, et al 2015), and are the primary source of livelihood to hundreds of millions of people (Spalding, et al 2017). Their immense structures are built through calcification, i.e., the continuous deposition of calcium carbonate that forms their skeletons. It has been proposed that membrane transporters and enzymes likely control both the ECM and ionic composition of vesicles by supplying calcium and bicarbonate and by removing protons from these compartments (Sun, et al 2020)
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