Department of Integrative Biology, University of Texas at Austin, Austin, Texas.
Australian Institute of Marine Science, Townsville, QLD, Australia.
Mol Ecol. 2018 Aug;27(15):3103-3115. doi: 10.1111/mec.14774. Epub 2018 Jul 13.
Reef-building corals can increase their resistance to heat-induced bleaching through adaptation and acclimatization and/or by associating with a more thermo-tolerant strain of algal symbiont (Symbiodinium sp.). Here, we show that these two adaptive pathways interact. We collected Acropora millepora corals from two contrasting thermal environments on the Great Barrier Reef: cooler, mid-latitude Orpheus Island, where all corals hosted a heat-sensitive clade C Symbiodinium, and warmer, low-latitude Wilkie Island, where corals hosted either a clade C or a more thermo-tolerant clade D. Corals were kept in a benign common garden to reveal differences in baseline gene expression, reflecting prior adaptation/long-term acclimatization. Model-based analysis identified gene expression differences between Wilkie and Orpheus corals that were negatively correlated with previously described transcriptome-wide signatures of heat stress, signifying generally elevated thermotolerance of Wilkie corals. Yet, model-free analyses of gene expression revealed that Wilkie corals hosting clade C were distinct from Wilkie corals hosting clade D, whereas Orpheus corals were more variable. Wilkie corals hosting clade C symbionts exhibited unique functional signatures, including downregulation of histone proteins and ion channels and upregulation of chaperones and RNA processing genes, putatively representing constitutive "frontloading" of stress response genes. Furthermore, clade C Symbiodinium exhibited constitutive expression differences between Wilkie and Orpheus, indicative of contrasting life history strategies. Our results demonstrate that hosting alternative Symbiodinium types is associated with different pathways of local adaptation for the coral host. These interactions could play a significant role in setting the direction of genetic adaptation to global warming in the two symbiotic partners.
造礁珊瑚可以通过适应和驯化以及/或与更耐热的藻类共生体（Symbiodinium sp.）菌株相关联来提高对热诱导白化的抵抗力。在这里，我们表明这两种适应性途径相互作用。我们从大堡礁两个截然不同的热环境中收集了 Acropora millepora 珊瑚：较冷的中纬度 Orpheus 岛，所有珊瑚都寄生着对热敏感的 clade C Symbiodinium；较暖的低纬度 Wilkie 岛，珊瑚寄生着 clade C 或更耐热的 clade D。珊瑚被保存在良性的普通花园中，以揭示反映先前适应/长期驯化的基线基因表达差异。基于模型的分析确定了 Wilkie 和 Orpheus 珊瑚之间的基因表达差异，这些差异与先前描述的热应激全转录组特征呈负相关，表明 Wilkie 珊瑚的耐热性普遍提高。然而，无模型的基因表达分析表明，宿主 clade C 的 Wilkie 珊瑚与宿主 clade D 的 Wilkie 珊瑚不同，而 Orpheus 珊瑚则更具变异性。宿主 clade C 共生体的 Wilkie 珊瑚表现出独特的功能特征，包括组蛋白和离子通道的下调以及伴侣蛋白和 RNA 处理基因的上调，推测代表应激反应基因的组成型“前加载”。此外，clade C Symbiodinium 在 Wilkie 和 Orpheus 之间表现出组成型表达差异，表明存在相反的生活史策略。我们的结果表明，宿主替代 Symbiodinium 类型与珊瑚宿主的不同局部适应途径相关。这些相互作用可能在确定两个共生伙伴对全球变暖的遗传适应方向方面发挥重要作用。
