Abstract
BackgroundIn recent years, several types of molecular markers and new microscale skeletal characters have shown potential as powerful tools for phylogenetic reconstructions and higher-level taxonomy of scleractinian corals. Nonetheless, discrimination of closely related taxa is still highly controversial in scleractinian coral research. Here we used newly sequenced complete mitochondrial genomes and 30 microsatellites to define the genetic divergence between two closely related azooxanthellate taxa of the family Caryophylliidae: solitary Desmophyllum dianthus and colonial Lophelia pertusa.ResultsIn the mitochondrial control region, an astonishing 99.8 % of nucleotides between L. pertusa and D. dianthus were identical. Variability of the mitochondrial genomes of the two species is represented by only 12 non-synonymous out of 19 total nucleotide substitutions. Microsatellite sequence (37 loci) analysis of L. pertusa and D. dianthus showed genetic similarity is about 97 %. Our results also indicated that L. pertusa and D. dianthus show high skeletal plasticity in corallum shape and similarity in skeletal ontogeny, micromorphological (septal and wall granulations) and microstructural characters (arrangement of rapid accretion deposits, thickening deposits).ConclusionsMolecularly and morphologically, the solitary Desmophyllum and the dendroid Lophelia appear to be significantly more similar to each other than other unambiguous coral genera analysed to date. This consequently leads to ascribe both taxa under the generic name Desmophyllum (priority by date of publication). Findings of this study demonstrate that coloniality may not be a robust taxonomic character in scleractinian corals.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0654-8) contains supplementary material, which is available to authorized users.
Highlights
In recent years, several types of molecular markers and new microscale skeletal characters have shown potential as powerful tools for phylogenetic reconstructions and higher-level taxonomy of scleractinian corals
The putative control region was responsible for the mitogenome length variation observed at both inter- and intraspecific levels: small insertions and deletions (INDELs) ranging from 72 bp to 150 bp in length were detected in L. pertusa (16,150 bp), and the Italian (16,229 bp) and Chilean (16,310 bp) specimens of D. dianthus
If 0.01–1 % genetic divergence in mitochondrial genomes, combined with morphological differences, is a valid range at the interspecific level for genera within Scleractinia (e.g. Acropora divaricata vs Acropora aspera, and Porites okinawensis vs Porites panamensis, see Additional file 1.2a and 1.2b), the results of our study suggest that Chilean Desmophyllum "dianthus", with its apparently morphological variation, and Mediterranean and Atlantic L. pertusa and D. "dianthus" may be considered three different species within the same genus
Summary
Several types of molecular markers and new microscale skeletal characters have shown potential as powerful tools for phylogenetic reconstructions and higher-level taxonomy of scleractinian corals. Desmophyllum dianthus (Esper, 1794) and Lophelia pertusa (Linneus, 1758) are azooxanthellate scleractinian corals living in cold waters worldwide, with the exception of the polar seas [20,21,22]. Desmophyllum dianthus is a solitary but gregarious scleractinian species that actively contributes to the accretion of cold-water coral build-ups Planulae of this species preferentially settle on parental skeleton, producing "branching" structures that, in some cases, can be mistaken as irregular colonies (Fig. 1a). Lophelia pertusa is a colonial species, forming bush-like colonies that can exceed one metre in diameter It is the most common azooxanthellate frame-building scleractinian and the main component of the densest and most extensive cold-water coral bioconstructions known far (e.g. Norwegian continental shelf [22, 31]). Only one of the two species is present in some environments: e.g., D. dianthus forms the dense shallow-water bioconstructions in the Chilean fjords [40, 41], whereas L. pertusa dominates the Norwegian "Cold-Water Coral (CWC) reefs" [42, 43]
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