MEPS 315:167-175 (2006)  -  doi:10.3354/meps315167

Single host and symbiont lineages of hydrothermal-vent gastropods Ifremeria nautilei (Provannidae): biogeography and evolution

Yohey Suzuki1,*, Shigeaki Kojima2, Hiromi Watanabe2, Masae Suzuki1, Shinji Tsuchida1, Takuro Nunoura1, Hisako Hirayama1, Ken Takai1, Kenneth H. Nealson1,3, Koki Horikoshi1

1Extremobiosphere Research Center, Japan Agency for Marine-Earth Science & Technology, 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan
2Ocean Research Institute, The University of Tokyo, 1-15-1 Minamidai, Nakano, Tokyo 164-8639, Japan
3Department of Earth Sciences, University of Southern California, 3651 Trousdale Parkway, Los Angeles, California 90089-0740, USA

ABSTRACT: Hydrothermal-vent gastropods belonging to the genus Ifremeria of the family Provannidae, which derive their nutrition from chemoautotrophic bacterial endosymbionts, constitute an important faunal element in the ecology of deep-sea hydrothermal systems in the SW Pacific. In order to determine phylogenetic relationships between the hosts and endosymbionts of Ifremeria gastropods, as well as their fatty-acid profiles and bulk and compound-specific carbon-isotopic signatures, we analyzed Ifremeria gastropods from the Manus, North Fiji and Lau Back-Arc Basins in the SW Pacific. Partial sequences of the mitochondrial cytochrome c oxidase subunit I gene suggest that Ifremeria gastropods from the 3 basins belong to a single species, Ifremeria nautilei. Based on the 16S rRNA gene sequences and results from fluorescence in situ hybridization analysis, the gill endosymbionts of Ifremeria gastropods from the 3 basins were grouped in a single lineage of γ-Proteobacteria, with sequence similarities of >98.3%. Placement of the endosymbionts within this single lineage was supported by fatty-acid profiles and carbon-isotopic compositions of the Ifremeria gastropods. Phylogenetic relationships inferred among gastropod hosts and among their endosymbionts were not congruent, implying that acquisition of endosymbionts might be from the environment rather than through vertical transmission. Differences in geographical distribution and host speciation pattern between the confamilial Alviniconcha and Ifremeria gastropods might be attributed to the remarkable differences in symbiotic strategy with chemoautotrophic bacteria.

KEY WORDS: Chemoautotrophic bacteria · Endosymbiosis · Provannidae · Gastropod

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