Data from: Evidence for a host role in thermotolerance divergence between populations of the mustard hill coral (Porites astreoides) from different reef environments

Studying the mechanisms that enable coral populations to inhabit spatially varying thermal environments can help evaluate how they will respond in time to the effects of global climate change and elucidate the evolutionary forces that enable or constrain adaptation. Inshore reefs in the Florida Keys experience higher temperatures than offshore reefs for prolonged periods during the summer. We conducted a common garden experiment with heat stress as our selective agent to test for local thermal adaptation in corals from inshore and offshore reefs. We show that inshore corals are more tolerant of a 6-week temperature stress than offshore corals. Compared with inshore corals, offshore corals in the 31 °C treatment showed significantly elevated bleaching levels concomitant with a tendency towards reduced growth. In addition, dinoflagellate symbionts (Symbiodinium sp.) of offshore corals exhibited reduced photosynthetic efficiency. We did not detect differences in the frequencies of major (>5%) haplotypes comprising Symbiodinium communities hosted by inshore and offshore corals, nor did we observe frequency shifts (‘shuffling’) in response to thermal stress. Instead, coral host populations showed significant genetic divergence between inshore and offshore reefs, suggesting that in Porites astreoides, the coral host might play a prominent role in holobiont thermotolerance. Our results demonstrate that coral populations inhabiting reefs <10-km apart can exhibit substantial differences in their physiological response to thermal stress, which could impact their population dynamics under climate change.

探究珊瑚种群适应空间异质性热环境的内在机制，有助于评估其对全球气候变化影响的实时响应，并阐明调控或限制适应性演化的进化动力。夏季期间，佛罗里达礁岛群（Florida Keys）的近岸礁体比远岸礁体经历更长时间的高温环境。我们以热胁迫作为选择压力开展了共同花园实验（common garden experiment），以此检验近岸与远岸礁体珊瑚的本地热适应性。实验结果表明，相较于远岸珊瑚，近岸珊瑚对为期6周的温度胁迫具有更强的耐受性。在31℃处理组中，远岸珊瑚的白化程度显著高于近岸珊瑚，同时伴随生长速率下降的趋势。此外，远岸珊瑚的虫黄藻（Symbiodinium sp.）光合效率有所降低。我们未检测到近岸与远岸珊瑚所携带的虫黄藻群落中，占比>5%的主要单倍型（haplotype）频率存在差异，也未观察到热胁迫引发的单倍型频率偏移（即‘重组’）现象。与之相反，近岸与远岸礁体的珊瑚宿主种群间存在显著的遗传分化，这表明在星状微孔珊瑚（Porites astreoides）中，珊瑚宿主可能在共生体（holobiont）的热耐受性中发挥主导作用。本研究结果证实，栖息在相距不足10公里的礁体中的珊瑚种群，对热胁迫的生理响应可存在显著差异，这可能会影响气候变化背景下其种群动态。