Table_1_On the genetic diversity of Chimaera monstrosa Linnaeus, 1758 (Chordata, Chondrichthyes, Holocephali) in the Mediterranean Sea.XLSX

The sustainable management and conservation of deep-sea species may be hampered by the paucity of data on their population structure and connectivity, in the face of ever-increasing fisheries pressure and other forms of impacts on deep-sea ecosystems. The rabbit fish, Chimaera monstrosa, is a deep-sea cartilaginous fish, reported worldwide in the past, but currently distributed only in the North-Eastern Atlantic Ocean and Mediterranean Sea. It is currently experiencing high levels of mortality associated with by-catch. Its slow growth, low fecundity and late maturity make this species particularly vulnerable to anthropogenic impact, although little is known about processes of connectivity between ecoregions. This study utilized DNA sequencing of the mitochondrial cytochrome c oxidase subunit I (COI) gene to investigate the population structure and demography of C. monstrosa both at the small (around the coasts of Sardinia, western Mediterranean Sea) and at larger spatial scales (at the pan-Mediterranean level, and between the Atlantic Ocean and the Mediterranean Sea). A total of 100 new sequences were obtained from specimens of Mediterranean origin, identifying 15 new haplotypes out of the 30 known so far for the species. Evidence of feeble but significant differentiation was detected among locations within the Tyrrhenian basin. Bayesian clustering analyses indicated the occurrence of three distinct haplogroups: the most common spread all over the Mediterranean, and the other two limited to the Western basin. Greater levels of genetic differentiation were found between the Atlantic and Mediterranean populations which constituted two main genetic clusters, with no shared haplotypes. The two populations became separated at the end of the Middle Pleistocene, with a clear sign of demographic expansion during the same period. The rabbit fish constitutes an important exception to a general paradigm of deep-sea species being connected by high levels of gene flow and such results could be useful to implement current management strategies to conserve this vulnerable by-caught species.

受限于深海物种种群结构与连通性相关数据的匮乏，加之渔业压力持续攀升、深海生态系统正遭受多重人类活动干扰，此类物种的可持续管理与保护工作往往受到掣肘。兔银鲛（Chimaera monstrosa）是一种深海软骨鱼类，历史上曾在全球海域被记录，但目前仅分布于东北大西洋与地中海海域。当前该物种因副渔获问题面临极高死亡率。该物种生长缓慢、繁殖力低下且性成熟较晚，使其极易受到人类活动的影响，但目前学界对其不同生态区域间的连通过程仍知之甚少。本研究通过对线粒体细胞色素c氧化酶亚基I（COI）基因进行DNA测序，分别在小尺度（地中海西部撒丁岛周边海域）与大空间尺度（泛地中海尺度，以及大西洋与地中海海域之间）下，对兔银鲛的种群结构与种群历史动态开展了调查。研究共计从地中海海域的样本中获取了100条全新序列，在该物种目前已知的30种单倍型中，新发现了15种单倍型。在第勒尼安海盆内部的采样点位间，检测到了微弱但显著的遗传分化信号。贝叶斯聚类分析结果显示，存在3个独立的单倍型类群：其中最为常见的类群广泛分布于整个地中海海域，另外两个类群则仅局限于地中海西部海域。大西洋与地中海种群间的遗传分化程度更高，二者构成了两个主要的遗传聚类群，且不存在共享单倍型。这两个种群在中更新世末期发生分化，同期还出现了显著的种群扩张迹象。通常认为深海物种依靠高水平的基因流实现种群连通，而兔银鲛则是这一普遍认知范式的重要例外。本研究结果可为当前针对这一易受影响的副渔获物种的保护管理策略提供科学支撑。