The evolution interactions of coral-Symbiodiniaceae

Altering the composition of Symbiodiniaceae community to adapt to anomalous sea water warming represents a potential survival mechanism for Scleractinian corals. However, despite our understanding of the close intimate relationship between coral hosts and Symbiodiniaceae, the processes of Symbiodiniaceae assembly and the long-standing evolution of coral-Symbiodiniaceae interactions remain unclear. This study utilized ITS2 amplicon sequencing and the SymPortal analysis framework to investigate the diversity and specificity of Symbiodiniaceae across 39 Scleractinian coral species distributed in the Luhuitou fringing reef in the South China Sea. The COI, ITS1, ITS-coral-specific and 18S rRNA gene sequences were concatenated in the phylogenetic analysis of coral hosts. Phylosymbiotic and cophylogenetic relationships between the coral hosts and their Symbiodiniaceae were also examined. Cladocopium and Durusdinium were identified as the predominant Symbiodiniaceae. The results reveal extensive host specificity in Symbiodiniaceae, particularly within Durusdinium, yet no phylosymbiotic signals between Symbiodiniaceae and hosts were observed, suggesting that Symbiodiniaceae community composition does not reflect host phylogeny. However, Cladocopium exhibited a significant cophylogenetic relationship with their hosts, especially with Complexa. Additionally, host-swap events were more prevalent than cospeciation, suggesting that host-swap speciation may be the main driver in the diversification of Symbiodiniaceae. Our findings emphasize a closer relationship between Cladocopium and coral hosts in comparison to that between Durusdinium and hosts, suggesting the flexibility of Durusdinium and coral hosts associations. The results of this study are helpful for understanding the evolutionary interactions between corals and its Symbiodiniaceae and their adaptability to environmental changes.