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Zoological Science
Abstract
Millepora (Cnidaria: Hydrozoa: Milleporidae) spp. are distributed throughout shallow subtropical and tropical marine environments in the Indo-Pacific and Caribbean-Atlantic, and have traditionally been identified using pore characteristics and colony form. Until now, representatives of Millepora spp. on the island of Okinawa-jima, Japan, have been divided into five species; three branching species (Millepora intricata, M. tenera, M. dichotoma), one species with plate-like morphology (M. platyphylla), and one encrusting species (M. exaesa). There have been only a few reports from the Indo-Pacific that have studied the genetic diversity within Millepora spp., although phylogenetic analyses in the Caribbean-Atlantic have proven useful in delimiting closely-related species, while demonstrating that morphologically-based identification systems may have problems. In the present study, we sought to clarify taxonomic confusion of Millepora spp. in the Pacific by using sequence data of the ribosomal internal transcribed spacer (ITS-rDNA) of specimens from Okinawa, Japan and other localities (Johnston Atoll, Great Barrier Reef). Four separate clades were recovered from the ITS-rDNA analyses. Although we examined specimens of all three branching Millepora spp. previously reported from Okinawa-jima Island, in our phylogenetic analyses they were concentrated within a single clade, with only three specimens in other clades. Encrusting Millepora specimens were found within all clades, although it should be noted all species initially start as encrusting forms, and plate-like specimens were found within three clades. Our data also point to the existence of a previously unknown lineage within Millepora characterized by its ability to overgrow live scleractinian corals.
The authors thank Dr. Y. Miyazaki (University of the Ryukyus; UR) for help with CT images, and Professor M. Hidaka and Associate Professor M. Toda (both UR) for reviewing an earlier version of this study. Members of the Molecular Invertebrate Systematics and Ecology (MISE) laboratory at UR, and Dr. T. Soliman, Dr. K. Wakeman (both Okinawa Institute of Science and Technology), and J. Gordon (MISE) offered opinions and information. The second author received funding from the Japanese Society for the Promotion of Science Postdoctoral Fellowship for Overseas Researchers and the two Marie Curie Actions of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA grant agreements 302957 and 600391 (FELLOWSEA: Campus do Mar International Fellowship Program). The Agencia Canaria de Investigación (ACIISI) and Fondo Social Europeo supported the third author's internship in Okinawa, Japan where the study was performed. Support was also provided by a Japan Society for the Promotion of Science ‘Zuno-Junkan’ grant entitled ‘Studies on origin and maintenance of marine biodiversity and systematic conservation planning’, and the International Research Hub Project for Climate Change and Coral Reef/Island Dynamics at UR to the senior author. The Census of Coral Reef Ecosystems' Australian node (CReefs: a field project of the Census of Marine Life), Dr. J. Caley, and S. Smith (both Australian Institute of Marine Science) provided specimens from Australia. Dr. R. Kosaki (chief scientist) and the crew of the Hi'ialakai are thanked for specimens from Johnston Atoll. Three anonymous reviewers' comments helped improve an earlier version of this work.
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