[B-CG07] 微化石生物学の最前線

[BCG07-P07] Genetic diversity of Globigerina bulloides in the Northwest Pacific Ocean

*Zeynab Zandvakili¹、Takuya Sagawa²、Kengo Kukita¹、Issui Ikuma¹、Yoshiyuki Ishitani³、Yurika Ujiie^1,4 (1.Kochi University、2.Institute of Science and Engineering, Faculty of Geosciences and Civil Engineering, Kanazawa University、3.Institute for Extra-Cutting-Edge Science and Technology Avant-garde Research (X-star), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan、4.Marine Core Research Institute, Kochi University, Nankoku, Japan)

キーワード：Planktonic foraminifera, Genetic diversity, Phylogeography

Planktonic foraminifera are widely used as the marine environment proxy. The species have been traditionally classified based on shell morphologies, and so called them as morphospecies. These morphospecies show specific geographic distributions associating with marine environments and ocean structure. However, molecular phylogenetic studies have revealed that each morphospecies contains genetically distinct species (genetic types), which have often shown different distribution patterns due to own ecological character. The morphospecies Globigerina bulloides is widely distributed from transitional to subpolar regions, though this species has rich variation in morphology. The previous molecular phylogeographic studies have found multiple genetic types in the world oceans, indeed, these morphological variations may be according to different genetic types. In the northwest Pacific Ocean, variable morphological specimens have been found from sediments indicating the possible presence of multiple genetic types. Here, we examined genetic diversity of G. bulloides and their distributions associating with the ocean structure in the poorly studied area, northwest Pacific Ocean. We collected living planktonic foraminiferal specimens using plankton-net towing at different layers between the surface and 750m water depth from four stations in the Kuroshio and Oyashio Current areas. In total, 180 specimens of G. bulloides were obtained from the upper of annual thermocline. The partial SSU rDNA phylogeny of G. bulloides with our new sequences showed two distinct clades, each of them was consisted of two subclades, with high bootstrap support. The two major clades are corresponded to marine environments: warm and cold waters, over the world. Our sequences were placed in three out of four subclades. All specimens obtained from the Oyashio Current area placed in one of two cold-water subclades. Some specimens obtained from the Kuroshio Current area placed in another cold-water subclade, though most specimens were in one of warm-water subclades. Thus, G. bulloides genetic types are separately distributed between the Oyashio and Kuroshio Currents, suggesting that ocean currents act as the barrier to the gene flow. The morphological characteristics of these genetic types will have an insight to distinguish “warm” or “cold” type of G. bulloides from sediment samples in future.