Evolutionary relationships among deep-sea mytilids (Bivalvia: Mytilidae) from hydrothermal vents and cold-water methane/sulfide seeps |
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Authors: | C Craddock W R Hoeh R G Gustafson R A Lutz J Hashimoto R J Vrijenhoek |
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Institution: | (1) Center for Theoretical and Applied Genetics, and Institute of Marine and Coastal Sciences, Rutgers University, 08903-0231 New Brunswick, New Jersey, USA;(2) Japan Marine Science and Technology Center, 2-15 Natsushima-Cho, 237 Yokosuka, Japan |
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Abstract: | A protein electrophoretic survey of mytilids inhabiting deep-sea hydrothermal vents and cold-water methane/sulfide seeps revealed electromorph patterns diagnostic of 10 distinct species. From hydrothermal vents located at sites on the Galápagos Rift, the Mid-Atlantic Ridge, and the Mariana Back Arc Basin, we detected four species of mytilids. Six additional species were detected from three cold-water seep sides in the Gulf of Mexico. The patchy distribution and temporal stability of seeps may provide a greater opportunity for mytilid diversification and persistence than vent sites Nei's genetic distances (D) between species were relatively large (range: 0.528 to ) both within and among habitat types. This pronounced degree of genetic differentiation suggests a relatively ancient common ancestor for the group. Phylogenetic trees were generated using distance Wagner and parsimony analyses of allozyme and morphological characters. The tree topologies obtained from both methods support: (1) the hypothesis that a seep ancestor gave rise to the deep-sea hydrothermal vent mytilids, (2) a historical progression from shallow-water to deep-water habitats, and (3) a co-evolutionary progression from external to internal localization of bacterial symbionts. Whether the seep mytilid taxa constitute paraphyletic or polyphyletic groups remains unresolved. Our phylogenetic hypotheses also provide a benchmark for the phylogeny of mytilid bacterial symbionts. |
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