A total of 10 specimens of Alcyonacea corals were collected at depths ranging from 905 m to 1 633 m by the manned submersible Shenhai Yongshi during two cruises in the South China Sea (SCS). Based on mitochondrial genomic characteristics, morphological examination, and sclerite scanning electron microscopy, the samples were categorized into four suborders (Calcaxonia, Holaxonia, Scleraxonia, and Stolonifera), and identified as 9 possible new cold-water coral species. Assessments of GC-skew dissimilarity, phylogenetic distance, and average nucleotide identity (ANI) revealed a slow evolutionary rate for the octocoral mitochondrial sequences. The nonsynonymous ( Ka) to synonymous ( Ks) substitution ratio ( Ka/ Ks) suggested that the 14 protein-coding genes (PCGs) were under purifying selection, likely due to specific deep-sea environmental pressures. Correlation analysis of the median Ka/ Ks values of five gene families and environmental factors indicated that the genes encoding cytochrome b (cyt b) and DNA mismatch repair protein ( mutS) may be influenced by environmental factors in the context of deep-sea species formation. This study highlights the slow evolutionary pace and adaptive mechanisms of deep-sea corals.
在“深海勇士”号载人潜水器在南海进行了两次科考过程中，在905米至1 633米的深度范围内共采集了10株软珊瑚目珊瑚。利用线粒体基因组特征结合形态学特征分析表明，所收集的冷水珊瑚新种隶属于Calcaxonia、Holaxonia、Scleraxonia和Stolonifera 4个亚目，代表了9个新种。线粒体基因组GC-skew、系统发育距离和平均核苷酸相似度的差异分析显示，八放珊瑚线粒体序列的进化较为缓慢。非同义( Ka)和同义( Ks)替换( Ka/ Ks)比值表明，14个蛋白质编码基因(PCGs)受净化选择，选择压力可能来自特定的深海环境。5个基因家族的 Ka/ Ks中值与环境因子的相关性分析发现，编码细胞色素 b (cyt b)和DNA错配修复蛋白( mutS)的基因可能受到环境因子的驱动在而形成深海物种过程中发挥重要作用。该研究强调了深海珊瑚的缓慢进化和深海适应机制。.
Keywords: Alcyonacea; Environmental factors; Ka/Ks evolution; Mitochondrial genome.