Tubastraea coccinea (Cnidaria: Anthozoa) is the globally dispersed species of Sun Coral

Abstract

Species of the genus Tubastraea (sun corals) have dispersed globally over recent decades, but morphological trait identification has led to taxonomic confusion, with multiple authors proposing conflicting species identifications due to high morphological plasticity and overlapping diagnostic traits. We combined global-scale molecular phylogenetics with chromosome-level genome assemblies to resolve this taxonomic issue. Using mitochondrial and nuclear markers from 287 specimens across five ocean regions, including type localities in Bora Bora (T. coccinea) and Galapagos (T. tagusensis), we reconstructed phylogenetic relationships and inferred demographic history through approximate Bayesian computation. We also generated high-quality, chromosome-level genome assemblies for three morphologically distinct morphotypes from the Brazilian coastline. Phylogenetic and species delimitation analyses revealed two well-supported clades: a small, geographically restricted T. tagusensis clade confined to the Galapagos Islands, and a large cosmopolitan clade containing all worldwide samples, including T. coccinea from its type locality. Comparative genomic analyses of the three morphotypes revealed k-mer spectra compatible with triploidy and assemblies comprising 14 chromosome-scale scaffolds with extensive synteny and gene-tree discordance consistent with incomplete lineage sorting. Dispersal-route analyses identified the Southeastern Pacific (Galapagos) as the ancestral source, with at least two independent, human-mediated colonization events establishing populations in the Southwestern Atlantic, Gulf of Mexico, and Western Pacific. Our results establish Tubastraea coccinea as the cosmopolitan species responsible for global dissemination, while T. tagusensis is endemic to the Galapagos and not involved in the worldwide dispersion.