Ochoa-Zavala Maried, Mar-Silva Adan Fernando, Pérez-Rodríguez Rodolfo, Palacios-Barreto Paola, Adams Douglas H, Blanco-Parra María Del Pilar, Díaz-Jaimes Píndaro
Escuela Nacional de Estudios Superiores, unidad Morelia, Laboratorio de Genética Evolutiva de Organismos Tropicales, Universidad Nacional Autónoma de México, Morelia, Mexico.
Unidad Académica de Ecología y Biodiversidad Acuática, Instituto de Ciencias del Mar y Limnología. Universidad Nacional Autónoma de México, Ciudad de Mexico, Mexico.
J Fish Biol. 2025 Feb;106(2):403-419. doi: 10.1111/jfb.15961. Epub 2024 Oct 15.
The apparent lack of physical barriers in the marine realm has created the conception that many groups have a constant gene flow. However, changes in ocean circulation patterns, glacial cycles, temperature, and salinity gradients are responsible for vicariant events in many fish species, including sharks. The bonnethead shark, Sphyrna tiburo, is an endangered small coastal shark species. Although considerable efforts have recently been undertaken, little remains known about the possible biogeographic scenario that can explain its actual distribution within the western Atlantic (WA). Here, we used 599 mitochondrial sequences to assess the phylogeographic structure and implement Bayesian phylogenetic analyses to obtain divergence times and reconstruct the ancestral geographic range. This allowed us to infer processes responsible for the diversification of S. tiburo into major divergent lineages. Our results indicated that S. tiburo in the WA represents three independent lineages, with Brazilian samples differentiated into a distinct genetic cluster. The posterior probability of ancestral range analysis indicated that the species likely originated in the northern region (Carolina Province and the southern Gulf of Mexico), where it colonized southward through the uplifting of the Central American Isthmus (CAI). The Northern and Caribbean genetic clusters appear to have arisen from the intensification of the Loop Current, which currently flows northward passing the Yucatan Peninsula, Gulf of Mexico, and east Florida. Following initial colonization, the Northeastern Brazil group differentiated from the Caribbean region due to the sediment and freshwater discharge of the Amazon-Orinoco Plume. Thus, the evolutionary history of the S. tiburo complex can be explained by a combination of dispersal and vicariance events that occurred over the last ~5 million years (MY). We established and confirmed the species and population limits, demonstrating that the Amazon-Orinoco Plume constitutes a significant dispersal barrier for coastal sharks. Finally, we discuss some recommendations for the conservation of the bonnethead shark.
海洋领域明显缺乏物理屏障，这使得人们认为许多群体具有持续的基因流动。然而，海洋环流模式、冰川周期、温度和盐度梯度的变化是导致包括鲨鱼在内的许多鱼类物种发生替代事件的原因。窄头双髻鲨（Sphyrna tiburo）是一种濒危的小型沿海鲨鱼物种。尽管最近已经做出了相当大的努力，但对于能够解释其在西大西洋（WA）实际分布的可能生物地理情况仍知之甚少。在这里，我们使用了599个线粒体序列来评估系统地理结构，并进行贝叶斯系统发育分析以获得分歧时间并重建祖先地理范围。这使我们能够推断出导致窄头双髻鲨分化为主要不同谱系的过程。我们的结果表明，西大西洋的窄头双髻鲨代表三个独立的谱系，巴西的样本分化为一个独特的基因簇。祖先范围分析的后验概率表明，该物种可能起源于北部地区（卡罗来纳省和墨西哥湾南部），并通过中美洲地峡（CAI）的隆起向南扩散。北部和加勒比海基因簇似乎是由于墨西哥湾流的增强而形成的，目前该洋流向北流经尤卡坦半岛、墨西哥湾和佛罗里达州东部。在最初的扩散之后，巴西东北部群体由于亚马逊 - 奥里诺科河羽流的沉积物和淡水排放而与加勒比地区分化。因此，窄头双髻鲨复合体的进化历史可以用过去约500万年（MY）中发生的扩散和替代事件的组合来解释。我们确定并确认了物种和种群界限，表明亚马逊 - 奥里诺科河羽流构成了沿海鲨鱼的重要扩散屏障。最后，我们讨论了一些关于保护窄头双髻鲨的建议。
