Genetic Divergence and Polyphyly in the Octocoral Genus Swiftia [Cnidaria: Octocorallia], Including a Species Impacted by the DWH Oil Spill

Abstract

Mesophotic coral ecosystems (MCEs) are recognized around the world as diverse and ecologically important habitats. In the northern Gulf of Mexico (GoMx), MCEs are rocky reefs with abundant black corals and octocorals, including the species Swiftia exserta. Surveys following the Deepwater Horizon (DWH) oil spill in 2010 revealed significant injury to these and other species, the restoration of which requires an in-depth understanding of the biology, ecology, and genetic diversity of each species. To support a larger population connectivity study of impacted octocorals in the GoMx, this study combined sequences of mtMutS and nuclear 28S rDNA to confirm the identity of Swiftia sea fans in the GoMx, compare these markers for different polyp colors in the GoMx and Atlantic, and examine the phylogeny of the genus. Two mtMutS haplotypes were identified, one seemingly endemic to the northern GoMx. Compared to other North Atlantic Swiftia, S. exserta, the type of the genus was found to be extremely divergent and distinct from the two other Swiftia at both loci, with strong evidence of polyphyly in the genus. This information refines our understanding of the geographical distribution of injured coral and highlights how little is known about MCEs. Substantial taxonomic revisions may be needed for several taxa injured by the DWH oil spill.

Evolution of mitochondrial and nuclear genomes in Pennatulacea

“…Such discordance has been attributed to Introgression, hybridization, and incomplete lineage sorting (e.g., Toews and Brelsford, 2012) and is not uncommon. For example, among octocorals, Frometa et al (2021) found that nuclear 28S rRNA and mitochondrial MutS sequences were not phylogenetically congruent in work with the genus Swiftia. As the mitochondrial protein coding genes are effectively a single locus, high concordance among mitochondrial genes can lead to high bootstrap values even when the tree topology reflects the evolutionary history of the mitochondrion rather than the organism.…”