Phylogenetic affinities of an enigmatic nannoplankton,Braarudosphaera bigelowii based on the SSU rDNA sequences |
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| Institution: | 1. Department of Earth and Planetary Sciences, Graduate School of Sciences, Kyushu University, Fukuoka 812-8581, Japan;2. Japan Agency for Marine-Earth Science and Technology, Yokosuka 237-0061, Japan;3. Pusan National University, Busan 609-735, Republic of Korea;1. Institut für Chemie und Biologie des Meeres (ICBM), Carl von Ossietzky Universität Oldenburg, Postfach, Oldenburg, Germany;2. Department of Subsurface Geobiological Analysis and Research, Japan Agency for Marine-Earth Science Technology (JAMSTEC), Yokosuka, Japan;1. Earthquake Research Institute, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan;2. Department of Chemistry, Biology, and Marine Science, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan;3. Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka 237-0061, Japan;4. Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba 305-8568, Japan;5. Division of Earth and Planetary Sciences, Graduate School of Science, Hokkaido University, N10 W8, Kita-ku, Sapporo 060-0810, Japan;1. V.I. Il''ichev Pacific Oceanological Institute, Far East Branch of Russian Academy of Science, (FEB of RAS), Vladivostok 690041, Russian Federation;2. Far Eastern Geological Institute, FEB of RAS, Vladivostok 690022, Russian Federation;3. North-Eastern Interdisciplinary Scientific Research Institute, FEB of RAS, Magadan, Russian Federation |
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| Abstract: | The phylogenetic position of an enigmatic calcareous nannoplankton Braarudosphaera bigelowii, whose taxonomic position has long been questioned, was investigated using molecular genetic methods. The SSU rDNA sequences of B. bigelowii were obtained using a single cell PCR technique independently from two single cells isolated from field samples. A BLAST search revealed that the SSU rDNA of B. bigelowii was most similar to those of the division Haptophyta. Subsequent phylogenetic analyses showed that B. bigelowii was included in a clade comprising members of the orders Isochrysidales and Coccolithales, the genus Chrysoculter and two unidentified haptophytes. Morphometric measurements of extant B. bigelowii populations were made to obtain precise information on their intraspecific size variation. The results showed that these populations could be subdivided into a small form (< 2.4 μm), an intermediate form A (4.0–5.3 μm), and an intermediate form B (5.3–7.2 μm), although the borders of the latter two forms overlapped. The SSU rDNA sequences showed the presence of 10-bp substitutions plus six insertions/deletions between specimens of intermediate forms A and B. The levels of DNA variation between them suggested that these two forms are genetically distinct from each other. |
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