In order to invade and adapt to deep-sea environments, shallow-water organisms have to acquire tolerance to high hydrostatic pressure, low water temperature, toxic methane and hydrogen sulfide, and feeding strategies ...In order to invade and adapt to deep-sea environments, shallow-water organisms have to acquire tolerance to high hydrostatic pressure, low water temperature, toxic methane and hydrogen sulfide, and feeding strategies not relying on photosynthetic products. Our previous study showed that the “evolutionary stepping stone hypothe-sis”, which assumes that organic falls can act as stepping-stones to connect shallow sea with deep sea, was supported in Mytilidae. However, it is not known whether other bivalves constituting chemosynthetic communities experienced the same evolutionary process or different processes from mytilid mussels. Therefore, here, we performed phylogenetic analyses by sequencing the nuclear 18S rRNA and mitochondrial COI genes of solemyid and thyasirid bivalves. In Solemyidae, the two genera Solemya and Acharax formed each clade, the latter of which was divided into three subgroups. The Solemya clade and one of the Acharax subgroups diverged in the order of shallow-sea residents, whale-bone residents, and deep-sea vent/seep residents, which supported the “evolutionary stepping stone hypothesis”. Furthermore, in Thyasiridae, the two genera Thyasira and Maorithyas formed a paraphyletic group and the other genera, Adontorhina, Axinopsis, Axinulus, Leptaxinus, and Mendicula, formed a clade. The “evolu-tionary stepping stone hypothesis” was not seemingly supported in the other lineages of Solemyidae and Thyasiridae.展开更多
Dispersal ability and environmental adaptability are profoundly associated with colonization and habitat segregation of deep-sea animals in chemosynthesis-based communities, because deep-sea seeps and vents are patchi...Dispersal ability and environmental adaptability are profoundly associated with colonization and habitat segregation of deep-sea animals in chemosynthesis-based communities, because deep-sea seeps and vents are patchily distributed and ephemeral. Since these environments are seemingly highly different, it is likely that vent and seep populations must be genetically differentiated by adapting to their respective environments. In order to elucidate dispersal ability and environmental adaptability of deep-sea mussels, we determined mitochondrial ND4 sequences of Bathymodiolus platifrons and B. japonicus obtained from seeps in the SagamiBayand vents in the Okinawa Trough. Among more than 20 species of deep-sea mussels, only three species in the Japanese waters including the above species can inhabit both vents and seeps. We examined phylogenetic relationships, genetic divergences (Fst), gene flow (Nm), and genetic population structures to compare the seep and vent populations. Our results showed no genetic differentiation and extensive gene flow between the seep and vent populations, indicating high dispersal ability of the two species, which favors colonization in patchy and ephemeral habitats. Our results also indicate that the environmental type (vent or seep) is not the primary factor responsible for habitat segregation in the two species.展开更多
文摘In order to invade and adapt to deep-sea environments, shallow-water organisms have to acquire tolerance to high hydrostatic pressure, low water temperature, toxic methane and hydrogen sulfide, and feeding strategies not relying on photosynthetic products. Our previous study showed that the “evolutionary stepping stone hypothe-sis”, which assumes that organic falls can act as stepping-stones to connect shallow sea with deep sea, was supported in Mytilidae. However, it is not known whether other bivalves constituting chemosynthetic communities experienced the same evolutionary process or different processes from mytilid mussels. Therefore, here, we performed phylogenetic analyses by sequencing the nuclear 18S rRNA and mitochondrial COI genes of solemyid and thyasirid bivalves. In Solemyidae, the two genera Solemya and Acharax formed each clade, the latter of which was divided into three subgroups. The Solemya clade and one of the Acharax subgroups diverged in the order of shallow-sea residents, whale-bone residents, and deep-sea vent/seep residents, which supported the “evolutionary stepping stone hypothesis”. Furthermore, in Thyasiridae, the two genera Thyasira and Maorithyas formed a paraphyletic group and the other genera, Adontorhina, Axinopsis, Axinulus, Leptaxinus, and Mendicula, formed a clade. The “evolu-tionary stepping stone hypothesis” was not seemingly supported in the other lineages of Solemyidae and Thyasiridae.
文摘Dispersal ability and environmental adaptability are profoundly associated with colonization and habitat segregation of deep-sea animals in chemosynthesis-based communities, because deep-sea seeps and vents are patchily distributed and ephemeral. Since these environments are seemingly highly different, it is likely that vent and seep populations must be genetically differentiated by adapting to their respective environments. In order to elucidate dispersal ability and environmental adaptability of deep-sea mussels, we determined mitochondrial ND4 sequences of Bathymodiolus platifrons and B. japonicus obtained from seeps in the SagamiBayand vents in the Okinawa Trough. Among more than 20 species of deep-sea mussels, only three species in the Japanese waters including the above species can inhabit both vents and seeps. We examined phylogenetic relationships, genetic divergences (Fst), gene flow (Nm), and genetic population structures to compare the seep and vent populations. Our results showed no genetic differentiation and extensive gene flow between the seep and vent populations, indicating high dispersal ability of the two species, which favors colonization in patchy and ephemeral habitats. Our results also indicate that the environmental type (vent or seep) is not the primary factor responsible for habitat segregation in the two species.
