Mechanism of segregation of gastropods corresponding to phylogeny of endosymbiotic bacteria in hydrothermal vent fields in the southwestern Pacific

利用SHINKAI 6500潜水器于2009年9月20日至21日在西南太平洋马努斯和北斐济盆地的深海热液喷口区进行了以化学合成为基础的群落调查。2006年10月8日至4日。20世纪90年代以来，热液喷发方式和Alviniconcha螺类动物群发生了变化。与马里亚纳海槽和印度洋相比，西南太平洋Alviniconcha螺的种群规模一直保持在没有快速扩张的水平。对螺体周围海水样品的化学分析表明，Alviniconcha螺体栖息在10-20°C的H_2S含量较高的区域，而Ifremeria nautilei螺体栖息在4-8°C的H_2S含量较低的区域。在Alviniconcha螺的所有栖息地，ε-Proteobacteria密切相关的化学合成细菌的二氧化碳固定系统，使用反向TCA循环，占优势的浮游自由生活的细菌。只有在Viena森林网站在马努斯盆地，只有Alviniconcha蜗牛内共生与γ-变形菌分布，细菌相关的内共生体中检测到的水样。与γ-变形菌共生的Alviniconcha螺的分布受热液喷发方式的制约，而不是热液喷发的构造背景和热水的物理化学特征。虽然它们被认为对栖息地环境中的生物，物理和化学因素的变化很敏感，但与ε-Proteobacteria内共生的Alviniconcha蜗牛可能能够适应更广泛的这些因素。

Survey of chemosynthesis-based communities in the deep-sea hydrothermal vent fields in the Manus and North Fiji Basins in the southwestern Pacific was carried out using the submersible SHINKAI 6500 from Sept. 8 to Oct. 4, 2006. Changes of mode of hydrothermal venting and fauna containing Alviniconcha snails since 1990s were recognized. Population size of Alviniconcha snails in the southwestern Pacific was shown to have been maintained without rapid expansion in comparison with those in the Mariana Trough and the Indian Ocean. Chemical analyses of sea water samples collected around snails showed that Alviniconcha snails inhabit areas at 10-20°C where H_2S content is relatively high, while habitats of Ifremeria nautilei are areas at 4-8°C where H_2S content is at the undetectable level. At all habitats of Alviniconcha snails, epsilon-proteobacteria closely related to chemosynthetic bacteria with carbon dioxide fixation system using reverse TCA cycle, were dominated among planktonic free-living bacteria. Only at the Viena Woods site in the Manus Basin, where only Alviniconcha snails endosymbiosing with gamma-proteobacteria were distributed, bacteria related to the endosymbionts were detected in the water samples. Distribution of Alviniconcha snails endosynbiosing with gamma-proteobacteria is restricted by mode of hydrothermal venting rather than tectonic backgrounds of hydrothermal venting and physico-chemical characteristics of hot water. While they are thought to be sensitive to changes in biological, physical and chemical factors in the environments of their habitats, Alviniconcha snails endosynbiosing with epsilon-proteobacteria are probably able to adapt themselves to wider range of such factors.