Hierarchical population structure and habitat differences in a highly mobile marine species: the Atlantic spotted dolphin

Recent molecular studies have shown that highly mobile species with continuous distributions can exhibit fine-scale population structure. In this context, we assessed genetic structure within a marine species with high dispersal potential, the Atlantic spotted dolphin (Stenella frontalis). Using 19 microsatellite loci and mitochondrial control region sequences, population structure was investigated in the western North Atlantic, the Gulf of Mexico and the Azores Islands. Analyses of the microsatellite data identified four distinct genetic clusters, which were supported by the control region sequences. The highest level of divergence was seen between two clusters corresponding to previously-described morphotypes that inhabit oceanic and shelf waters. The combined morphological and genetic evidence suggests these two lineages are on distinct evolutionary trajectories and could be considered distinct subspecies despite their parapatry. Further analysis of the continental shelf cluster resulted in three groups: animals inhabiting shelf waters in the western North Atlantic, the eastern Gulf of Mexico, and the western Gulf of Mexico. Analyses of environmental data indicate the four genetic clusters inhabit distinct habitats in terms of depth and sea surface temperature. Contemporary dispersal rate estimates suggest all of these populations should be considered as distinct management units. Conversely, no significant genetic differentiation was observed between S. frontalis from offshore waters of the western North Atlantic and the Azores, which are separated by approximately 4500 km. Overall, the hierarchical structure observed within the Atlantic spotted dolphin shows that the biogeography of the species is complex because it is not shaped solely by geographic distance.

近年来的分子生物学研究表明，即便拥有连续分布范围的高移动性物种，也可能展现出精细尺度的种群遗传结构。在此研究背景下，我们针对一种具备高扩散能力的海洋物种——大西洋斑点海豚（Stenella frontalis）的种群遗传结构展开了评估。本研究利用19个微卫星位点（microsatellite loci）与线粒体控制区序列（mitochondrial control region sequences），对西北大西洋、墨西哥湾以及亚速尔群岛海域的大西洋斑点海豚种群结构进行了探究。微卫星数据分析共鉴定出四个独立的遗传聚类群，该结果得到了线粒体控制区序列分析的支持。两个聚类群之间的遗传分化程度最高，这两个聚类群分别对应此前已报道的栖息于大洋水域与陆架水域的两种形态型（morphotypes）。综合形态学与遗传学证据表明，这两个演化支系处于截然不同的演化路径之中，即便二者为邻域分布（parapatry），仍可被划分为独立的亚种。对陆架聚类群的进一步分析则将其划分为三个类群：栖息于西北大西洋陆架水域、墨西哥湾东部陆架水域以及墨西哥湾西部陆架水域的大西洋斑点海豚。环境数据分析结果显示，这四个遗传聚类群分别栖息于水深与海表温度特征各异的生境中。当代扩散速率的估算结果表明，上述所有种群均应被视为独立的管理单元（management units）。与之相反，在相距约4500公里的西北大西洋远海海域与亚速尔群岛海域的大西洋斑点海豚样本之间，未检测到显著的遗传分化。总体而言，大西洋斑点海豚种群内观测到的层级化种群结构表明，该物种的生物地理学格局较为复杂，其形成并非仅由地理距离所主导。