Data from: Host-targeted RAD-Seq reveals genetic changes in the coral Oculina patagonica associated with range expansion along the Spanish Mediterranean coast

Many organisms are expanding their ranges in response to changing environmental conditions. Understanding the patterns of genetic diversity and adaptation along an expansion front is crucial to assessing a species’ long-term success. While next-generation sequencing techniques can reveal these changes in fine detail, ascribing them to a particular species can be difficult for organisms that live in close association with symbionts. Using a novel modified restriction-site associated DNA sequencing (RAD-Seq) protocol to target coral DNA, we collected 595 coral-specific single nucleotide polymorphisms (SNPs) from 189 colonies of the invasive coral Oculina patagonica from the Spanish Mediterranean coast, including established core populations and two expansion fronts. Surprisingly, populations from the recent northern expansion are genetically distinct from the westward expansion and core populations, and also harbor greater genetic diversity. We found that temperature may have driven adaptation along the northern expansion, as genome scans for selection found three candidate loci associated with temperature in the north but none in the west. We found no genomic signature of selection associated with artificial substrate, which has been proposed for explaining the rapid spread of O. patagonica. This suggests that this coral is simply an opportunistic colonizer of free space made available by coastal habitat modifications. Our results suggest that unique genetic variation, possibly due to limited dispersal across the Ibiza Channel, an influx of individuals from different depths, and/or adaptation to cooler temperatures along the northern expansion front may have facilitated the northward range expansion of O. patagonica in the western Mediterranean.

诸多生物会随环境条件变化而拓展其分布范围。解析物种扩张前沿的遗传多样性与适应性模式，对于评估其长期存续能力至关重要。尽管新一代测序技术能够精细地揭示这类遗传变化，但对于与共生体紧密结合的生物而言，将这些变化归因于特定物种仍颇具挑战。本研究采用改良的新型限制性酶切位点相关DNA测序（restriction-site associated DNA sequencing, RAD-Seq）方案靶向珊瑚基因组，从西班牙地中海沿岸的入侵性珊瑚巴戈尼亚角珊瑚（Oculina patagonica）的189个珊瑚群落中，获取了595个珊瑚特异性单核苷酸多态性（single nucleotide polymorphisms, SNPs）位点，样本涵盖已定植的核心种群与两个扩张前沿种群。令人意外的是，近期向北扩张的种群在遗传层面与向西扩张种群及核心种群存在显著分化，且拥有更高的遗传多样性。基因组选择扫描结果显示，北部扩张区域存在3个与温度相关的候选基因座，而西部扩张区域未发现此类位点，这表明温度可能驱动了北部扩张过程中的适应性演化。本研究未发现与人工基质相关的选择基因组特征——此前有假说提出，人工基质可解释巴戈尼亚角珊瑚的快速扩散。这表明该珊瑚仅为机会主义定植者，利用沿海生境改造所腾出的空白空间实现扩张。本研究结果表明，独特的遗传变异——可能源于伊维萨海峡的有限扩散、不同深度个体的迁入，以及抑或北部扩张前沿对低温环境的适应性——可能促进了巴戈尼亚角珊瑚在地中海西部的向北扩张。