Oscillations in the Earth's temperature and the subsequent retreating and advancing of ice-sheets around the polar regions are thought to have played an important role in shaping the distribution and genetic structuring of contemporary high-latitude populations. After the Last Glacial Maximum (LGM), retreating of the ice-sheets would have enabled early colonizers to rapidly occupy suitable niches to the exclusion of other conspecifics, thereby reducing genetic diversity at the leading-edge. Bottlenose dolphins (genus Tursiops) form distinct coastal and pelagic ecotypes, with finer scale genetic structuring observed within each ecotype. We reconstruct the post-glacial colonization of the Northeast Atlantic (NEA) by bottlenose dolphins using habitat modelling and phylogenetics. The AquaMaps model hindcasted suitable habitat for the LGM in the Atlantic lower latitude waters and parts of the Mediterranean Sea. The time-calibrated phylogeny, constructed with 86 complete mitochondrial genomes including 30 generated for this study and created using a multi-species coalescent model, suggests that the expansion to the available coastal habitat in the NEA happened via founder events starting ~15,000 years ago (95% highest posterior density interval: 4,900-26,400). The founders of the two distinct coastal NEA populations comprised as few as two maternal lineages that originated from the pelagic population. The low effective population size and genetic diversity estimated for the shared ancestral coastal population subsequent to divergence from the pelagic source population are consistent with leading-edge expansion. These findings highlight the legacy of the Late Pleistocene glacial cycles on the genetic structuring and diversity of contemporary populations.

中文翻译：

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宽吻海豚对北部沿海栖息地的冰后殖民：海洋前沿扩张？

地球温度的波动以及随后极地周围冰盖的后退和前进被认为在塑造当代高纬度人群的分布和遗传结构方面发挥了重要作用。在末次盛冰期 (LGM) 之后，冰盖的后退将使早期殖民者能够迅速占据合适的生态位，排除其他同种生物，从而减少前沿的遗传多样性。宽吻海豚（Tursiops 属）形成了不同的沿海和远洋生态型，在每个生态型内观察到更精细的遗传结构。我们使用栖息地建模和系统发育学重建了宽吻海豚在东北大西洋 (NEA) 的冰川后殖民。AquaMaps 模型在大西洋低纬度水域和地中海部分地区为 LGM 提供了合适的栖息地。时间校准的系统发育由 86 个完整的线粒体基因组构建，其中 30 个为本研究生成并使用多物种合并模型创建，表明 NEA 可用沿海栖息地的扩展是通过大约 15,000 年前开始的创始人事件发生的。 95% 的最高后密度区间：4,900-26,400）。两个不同的沿海 NEA 种群的创始人仅包含两个源自远洋种群的母系谱系。在与远洋源种群发生分歧后，为共享祖先沿海种群估计的低有效种群规模和遗传多样性与前沿扩张一致。