Differential gene expression patterns with ontogeny following an in situ depth translocation of coral planulae. Differential gene expression patterns with ontogeny following an in situ depth translocation of coral planulae

Mesophotic coral reefs have been proposed as refugia for corals, providing shelter and larval propagules for shallow-water reefs that are disproportionately challenged by global climate change and local anthropogenic stressors. Yet, knowledge of the capacity of coral larvae to adjust to different depth environments is still limited. In this study, planulae of the reef-building coral Stylophora pistillata from 5-8 and 40-44 m depth in the Gulf of Aqaba were tested in a long-term in situ translocation experiment for their ability to settle and acclimate to reciprocal depth conditions. We assessed survival rates, photochemical, physiological and morphological characteristics, as well as gene expression variations in juveniles grown at different depths, comparing them to non-translocated adults, juveniles and planulae. We found high mortality rates among mesophotic-origin planulae, irrespective of translocation depth. Gene expression patterns suggested that deep planulae lacked settlement competency and experienced increased developmental stress upon release. Symbiont photochemical acclimation to depth occurred rapidly within 8 days, with symbiont populations showing changes in photochemical traits but no symbiont species shuffling between deep and shallow juveniles. In contrast, coral host physiological and morphological acclimation were less evident. We observed minimal overlap in gene expression patterns between different life stages and depths, indicating that gene expression significantly depends on life stage. The study also identified a set of DEGs associated with initial stress responses following translocation, lingering stress response, and environmental effects of depth. In conclusion, though our data reveal rapid symbiont acclimation, host acclimation to match deep coral phenotypes was incomplete within 60 days for planulae translocated to different depths. These results have implications for understanding the ecological significance of mesophotic reefs as potential larval sources in the face of environmental stressors. Overall design: We sampled coral planulae from shallow (5m) and mesophotic reefs (45m) in Eilat, Israel. Gene expression patterns of planulae and their parents from each depth were assessed with RNAseq (Illumina HTS). Planulae were placed in situ in a fully corssed reciprocal depth transplant design. Samples for RNAseq were again taken at 8 and 60 days old.

中光层珊瑚礁（mesophotic coral reefs）被认为是珊瑚的避难所，可为深受全球气候变化与当地人为胁迫不成比例影响的浅水珊瑚礁提供庇护场所与幼虫繁殖体。然而，目前学界对于珊瑚幼虫适应不同深度环境的能力认知仍较为有限。
本研究针对亚喀巴湾（Gulf of Aqaba）5-8米与40-44米深度的造礁珊瑚（reef-building coral）柱形珊瑚（Stylophora pistillata）的浮浪幼虫（planulae），开展了长期原位易位实验，以检测其在互易深度条件下的附着与适应能力。
研究团队评估了在不同深度环境中培育的幼体的存活率、光化学特性、生理特征与形态特征，以及基因表达变化，并将其与未发生易位的成体、幼体及浮浪幼虫进行对照。
实验结果显示，无论易位至何种深度，源自中光层的浮浪幼虫均表现出较高的死亡率。基因表达模式分析表明，深层浮浪幼虫缺乏附着能力，且在释放后会遭受更显著的发育胁迫。
共生体的光化学适应可在8天内快速完成，共生菌群仅出现光化学性状的改变，并未在深浅层幼体间发生共生体物种的替换。与之相对，珊瑚宿主的生理与形态适应则并不明显。
研究团队观察到，不同生命阶段与不同深度下的基因表达模式重叠度极低，这表明基因表达在很大程度上依赖于生命阶段。本研究还鉴定出一组与易位后初始胁迫响应、持续胁迫响应及深度环境效应相关的差异表达基因（DEGs, differentially expressed genes）。
综上，尽管本研究数据显示共生体可快速适应环境，但对于易位至不同深度的浮浪幼虫而言，其宿主要达到与深层珊瑚表型匹配的适应水平，在60天的实验周期内尚未完成。
这些研究结果有助于理解在环境胁迫背景下，中光层珊瑚礁作为潜在幼虫来源的生态意义。
总体实验设计：研究团队从以色列埃拉特（Eilat）的浅水（5米）与中光层礁（45米）采集珊瑚浮浪幼虫。利用RNA测序（RNAseq，Illumina高通量测序（Illumina HTS）），对各深度的浮浪幼虫及其亲本的基因表达模式进行评估。浮浪幼虫以完全交叉互易深度移植设计进行原位安置。分别在幼体培育至8天与60天时，再次采集样本用于RNA测序。