Genetic differentiation and host usage of coral and fire coral-associated barnacles (Cirripedia: Pyrgomatinae and Wanellininae) across the Indian and Pacific Oceans

Using two molecular markers (COI and 12S) collected from seven genera and 20 species of coral associated and fire coral-associated barnacles, we examined whether genetic differentiation occurs between the Indian (total 261 sequences) and Pacific populations (195 sequences). Molecular phylogenetic analysis revealed pyrgomatinid barnacles formed two major sister-clades: the Cantellius clade and the major clade. Most of the species in the Cantellius clade did not show Indo-Pacific genetic divergence, except Cantellius sextus, which formed sister Indian and Pacific Ocean clades. Within the major clade, Darwiniella angularis, Galkinius maculosus, Nobia grandis, and Hiroa stubbingsi were composed of well-supported clades corresponding to the Indian and Pacific Oceans. The fire coral-associated barnacles Wanella milleporae have molecular clades corresponding to the populations in the Red Sea, Phuket waters, and Pacific Ocean. Species delimitation analyses and haplotype network supported the divergence of sequences in some coral barnacle species and fire coral barnacle between Indian and Pacific populations. Indo-Pacific genetic differentiation in some species appears to have resulted from Pleistocene glaciations. Life-history traits, length of larval development period, and host specificity appear can further affect the differentiation of coral barnacles across the Indian and Pacific Oceans.