Center for Genomics and Systems Biology, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates.
Centre for Sustainable Ecosystem Solutions and School of Earth, Atmospheric and Life Sciences, University of Wollongong, Wollongong, NSW, Australia.
Mol Ecol. 2020 Mar;29(5):899-911. doi: 10.1111/mec.15372. Epub 2020 Feb 17.
Reef-building corals are at risk of extinction from ocean warming. While some corals can enhance their thermal limits by associating with dinoflagellate photosymbionts of superior stress tolerance, the extent to which symbiont communities will reorganize under increased warming pressure remains unclear. Here we show that corals in the hottest reefs in the world in the Persian Gulf maintain associations with the same symbionts across 1.5 years despite extreme seasonal warming and acute heat stress (≥35°C). Persian Gulf corals predominantly associated with Cladocopium (clade C) and most also hosted Symbiodinium (clade A) and/or Durusdinium (clade D). This is in contrast to the neighbouring and milder Oman Sea, where corals associated with Durusdinium and only a minority hosted background levels of Cladocopium. During acute heat stress, the higher prevalence of Symbiodinium and Durusdinium in bleached versus nonbleached Persian Gulf corals indicates that genotypes of these background genera did not confer bleaching resistance. Within symbiont genera, the majority of ITS2 rDNA type profiles were unique to their respective coral species, confirming the existence of host-specific symbiont lineages. Notably, further differentiation among Persian Gulf sites demonstrates that symbiont populations are either isolated or specialized over tens to hundreds of kilometres. Thermal tolerance across coral species was associated with the prevalence of a single ITS2 intragenomic sequence variant (C3gulf), definitive of the Cladocopium thermophilum group. The abundance of C3gulf was highest in bleaching-resistant corals and at warmer sites, potentially indicating a specific symbiont genotype (or set of genotypes) that may play a role in thermal tolerance that warrants further investigation. Together, our findings indicate that co-evolution of host-Symbiodiniaceae partnerships favours fidelity rather than flexibility in extreme environments and under future warming.
造礁珊瑚面临着因海洋变暖而灭绝的风险。虽然一些珊瑚可以通过与具有更高胁迫耐受能力的虫黄藻共生体结合来增强其热极限，但共生体群落在增加的变暖压力下将如何重组仍不清楚。在这里，我们展示了尽管经历了极端季节性升温和急性热胁迫（≥35°C），世界上波斯湾最热的珊瑚礁中的珊瑚仍能在 1.5 年内保持与相同共生体的联系。波斯湾珊瑚主要与 Cladocopium（类群 C）共生，大多数还与 Symbiodinium（类群 A）和/或 Durusdinium（类群 D）共生。这与相邻且较温和的阿曼海形成对比，在阿曼海，珊瑚与 Durusdinium 共生，只有少数珊瑚背景水平下存在 Cladocopium。在急性热胁迫下，与非白化珊瑚相比，白化珊瑚中 Symbiodinium 和 Durusdinium 的高流行率表明这些背景属的基因型并未赋予其抗白化能力。在共生体属内，大多数 ITS2 rDNA 型谱与其各自的珊瑚物种特有，证实了存在宿主特异性共生体谱系。值得注意的是，波斯湾各地点之间的进一步分化表明，共生种群要么是孤立的，要么是在数十到数百公里的范围内特化的。珊瑚物种的热耐受性与单个 ITS2 种内序列变异体（C3gulf）的流行程度相关，该变异体是 Cladocopium thermophilum 组的特征。C3gulf 在抗白化珊瑚和温暖地点的丰度最高，这可能表明一种特定的共生体基因型（或一组基因型）可能在耐热性方面发挥作用，值得进一步研究。总之，我们的研究结果表明，宿主-共生体的协同进化有利于在极端环境中和未来变暖条件下的保真度，而不是灵活性。
