Desmophyllum dianthus (Esper, 1794) in the scleractinian phylogeny and its intraspecific diversity

Abstract

The cosmopolitan solitary deep-water scleractinian coral Desmophyllum dianthus (Esper, 1794) was selected as a representative model species of the polyphyletic Caryophylliidae family to (1) examine phylogenetic relationships with respect to the principal Scleractinia taxa, (2) check population structure, (3) test the widespread connectivity hypothesis and (4) assess the utility of different nuclear and mitochondrial markers currently in use. To carry out these goals, DNA sequence data from nuclear (ITS and 28S) and mitochondrial (16S and COI) markers were analyzed for several coral species and for Mediterranean populations of D. dianthus. Three phylogenetic methodologies (ML, MP and BI), based on data from the four molecular markers, all supported D. dianthus as clearly belonging to the "robust" clade, in which the species Lophelia pertusa and D. dianthus not only grouped together, but also shared haplotypes for some DNA markers. Molecular results also showed shared haplotypes among D. dianthus populations distributed in regions separated by several thousands of kilometers and by clear geographic barriers. These results could reflect limited molecular and morphological taxonomic resolution rather than real widespread connectivity. Additional studies are needed in order to find molecular markers and morphological features able to disentangle the complex phylogenetic relationship in the Order Scleractinia and to differentiate isolated populations, thus avoiding the homoplasy found in some morphological characters that are still considered in the literature.

Figure 1. Phylogenetic relationship between Desmophyllum dianthus and principal taxa from Scleractinia families.

Tree topology was inferred by Bayesian analysis, based on combined mitochondrial and nuclear genes. R and C indicate “robust” and “complex” groups, respectively. Numbers on main branches show the Bayesian posterior probability and bootstrap support obtained under Maximum Parsimony and Maximum Likelihood criteria, respectively. Stars indicate other well-supported clades (pp≥95; bootstrap >70).

Figure 2. Relationship between Desmophyllum dianthus and principal taxa from Scleractinia families based on mitochondrial COI.

Phylogenetic relationships among D. dianthus and representative species of the family Caryophylliidae. R, C and B indicate “robust”, “complex” and “basal” groups, respectively. The phylogenetic relationships were inferred by BI, MP and ML criteria (numbers show the Bayesian posterior probability and bootstrap supports given at branches, respectively). Stars indicate other well-supported clades (pp≥95; bootstrap >70).

Figure 3. Haplotypes network.

Parsimony network of internal transcribed spacer (ITS) ribosomal DNA sequence haplotypes of Desmophyllum dianthus belonging to Mediterranean Sea populations (from this study) and South Pacific Ocean populations (in blue; from Miller et al. [35], [36]). Sizes of the circles are proportional to the number of samples presenting such haplotype. Numbers indicate the variable positions. A) Network based on depth (white = shallow <600 m; light green = medium 600–1000 m; dark green = deep >1000 m). B) Network based on sampling area (red = Ionian Sea; orange = Adriatic Sea; yellow = Strait of Sicily).