The deep-sea chemosynthetic environment is one of the most extreme environments on the Earth, with low oxygen, high hydrostatic pressure and high levels of toxic substances. Species of the family Vesicomyidae are among the dominant chemosymbiotic bivalves found in this harsh habitat. Mitochondria play a vital role in oxygen usage and energy metabolism; thus, they may be under selection during the adaptive evolution of deep-sea vesicomyids. In this study, the mitochondrial genome (mitogenome) of the vesicomyid bivalve Calyptogena marissinica was sequenced with Illumina sequencing. The mitogenome of C. marissinica is 17,374 bp in length and contains 13 protein-coding genes, 2 ribosomal RNA genes (rrnS and rrnL) and 22 transfer RNA genes. All of these genes are encoded on the heavy strand. Some special elements, such as tandem repeat sequences, “G(A)nT” motifs and AT-rich sequences, were observed in the control region of the C. marissinica mitogenome, which is involved in the regulation of replication and transcription of the mitogenome and may be helpful in adjusting the mitochondrial energy metabolism of organisms to adapt to the deep-sea chemosynthetic environment. The gene arrangement of protein-coding genes was identical to that of other sequenced vesicomyids. Phylogenetic analyses clustered C. marissinica with previously reported vesicomyid bivalves with high support values. Positive selection analysis revealed evidence of adaptive change in the mitogenome of Vesicomyidae. Ten potentially important adaptive residues were identified, which were located in cox1, cox3, cob, nad2, nad4 and nad5. Overall, this study sheds light on the mitogenomic adaptation of vesicomyid bivalves that inhabit the deep-sea chemosynthetic environment.
Paleozoic porphyry copper deposits are generally much less common than their Mesozoic or Cenozoic counterparts, as they can be completely eroded in rapidly uplifting arcs. There are, however, some large Paleozoic porphyry copper deposits preserved worldwide, especially in the Central Asian orogenic belt, although the processes by which these ancient porphyry deposits were preserved are poorly constrained. The Carboniferous Yandong porphyry copper deposit was selected as a case study to resolve this issue using a combination of thermal history models derived from low-temperature thermochronology data and regional geologic records. Our results show that Yandong preserves a record of at least two episodes of cooling separated by a phase of mild Middle Jurassic reheating. These two cooling events included one major event, linked to the Qiangtang collision or northward motion of Tarim plate during the late Permian to Triassic, and one minor event, possibly related to the Lhasa collision or closure of Mongol-Okhotsk Ocean from the Middle Jurassic to Early Cretaceous, respectively. Tectonic quiescence and limited exhumation prevailed from the Late Cretaceous to Cenozoic in the Yandong area. Combining our results with regional geologic records, we propose that extensional tectonic subsidence, postmineralization burial, dry paleoclimatic conditions, and Cenozoic tectonic quiescence were key factors for the preservation of Yandong. This study demonstrates that anomalously old apatite fission track ages, integrated with age-elevation relationships, can have implications for mineral exploration strategies in the Chinese Tianshan orogens.
This work reports on a preliminary taxonomic study of epibenthic macroinvertebrates collected or observed by underwater video at the Haima cold seeps and in adjacent deep-sea habitats, including a mud volcano field and Ganquan Plateau, during an expedition in the South China Sea by the Chinese-manned submersible Shenhai Yongshi in May 2018. A total of 41 species belonging to 6 phyla were identified, among which 34 species were collected from the Haima cold seeps. Mollusks and crustaceans that are specialized in reducing habitats were predominant in biotopes of the Haima cold seeps, whereas sponges and cold-water corals and their commensals were prominent in communities of the mud volcano field and the slopes of Ganquan Plateau. The distribution and faunal composition of each taxonomic group are discussed.
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