Data from: Genetic structure of coral-Symbiodinium symbioses on the world’s warmest reefs

Corals in the Arabian/Persian Gulf (PAG) survive extreme sea temperatures (summer mean: >34°C), and it is unclear whether these corals have genetically adapted or physiologically acclimated to these conditions. In order to elucidate the processes involved in the thermal tolerance of PAG corals, it is essential to understand the connectivity between reefs within and outside of the PAG. To this end, this study set out to investigate the genetic structure of the coral, Platygyra daedalea, and its symbiotic algae in the PAG and neighbouring Gulf of Oman. Using nuclear markers (the ITS region and an intron of the Pax-C gene), this study demonstrates genetic divergence of P. daedalea on reefs within the thermally extreme PAG compared with those in the neighbouring Gulf of Oman. Isolation by distance of P. daedalea was supported by the ITS dataset but not the Pax-C intron. In addition, the symbiont community within the PAG was dominated by C3 symbionts, while the purportedly thermotolerant clade D was extremely rare and was common only at sites outside of the PAG. Analysis of the psbAncr indicates that the C3 variant hosted by P. daedalea in the PAG belongs to the newly described species, Symbiodinium thermophilum. The structuring of the coral and symbiont populations suggests that both partners of the symbiosis may contribute to the high bleaching thresholds of PAG corals. While limited gene flow has likely played a role in local adaptation within the PAG, it also indicates limited potential for natural export of thermal tolerance traits to reefs elsewhere in the Indian Ocean threatened by climate change.阿拉伯/波斯湾（Arabian/Persian Gulf，以下简称PAG）的珊瑚可存活于极端海水温度环境（夏季平均水温＞34℃），目前尚不明确这些珊瑚是通过遗传适应还是生理驯化来适配此类极端条件。为阐明PAG珊瑚耐热性背后的相关机制，明确PAG内外珊瑚礁之间的连通性至关重要。为此，本研究旨在探究PAG及其邻近阿曼湾内的迷宫扁脑珊瑚（Platygyra daedalea）及其共生藻类的遗传结构。本研究利用核分子标记（ITS区域及Pax-C基因内含子）开展分析，结果显示：相较于邻近阿曼湾的种群，极端高温环境下PAG内的迷宫扁脑珊瑚种群存在遗传分化。基于ITS数据集的分析支持了迷宫扁脑珊瑚的距离隔离模式，但Pax-C基因内含子数据集并未验证该结果。此外，PAG内的共生藻群落以C3型共生体占主导，而据称具有耐热性的D分支则极为罕见，仅在PAG以外的采样点较为常见。对psbAncr标记的分析表明，PAG内迷宫扁脑珊瑚所宿主的C3型共生体隶属于最新描述的嗜热虫黄藻（Symbiodinium thermophilum）。珊瑚与共生藻的种群结构特征表明，共生双方可能共同促成了PAG珊瑚极高的白化耐受阈值。尽管有限的基因流可能在PAG内部的局部适应中发挥了作用，但这同时也意味着，将耐热性状自然扩散至印度洋其他受气候变化威胁的珊瑚礁的潜力十分有限。