Cryptic lineages respond differently to coral bleaching

Coral cover is decreasing worldwide largely as a result of a rise in seawater temperatures that triggers coral bleaching and induces coral mortality. How coral reefs will respond to climate change will be a function of genetic variation and how it is partitioned within and among species. A critical initial step is to accurately delineate species and quantify their physiological potential to cope with heat stress. Cryptic species are morphologically similar but genetically distinct and may respond physiologically different to climate change. A dominant Caribbean reef builder severely affected by climate change is the mountainous star coral, Orbicella faveolata. Recently, Dziedzic et al. (2019) reported quantitative genetic variation in the physiological response to thermal stress in a single population of this species, suggesting that variation within populations will allow these corals to adapt to rising ocean temperatures. We reanalyzed their data and found multiple cryptic lineages rather than a single panmictic population, with one of the lineages being not heat-tolerant. While different cryptic lineages co-occur in certain locations, there is at least one lineage that occurs only in a single location. Our finding of hidden lineages within a threatened species highlights the varying extinction risks faced by these independently evolving groups, especially when the prospects of survival under warmer oceans seem favorable for some of them only.

全球珊瑚覆盖率下降的主要诱因是海水温度升高，该环境变化会触发珊瑚白化并诱导珊瑚死亡。珊瑚礁对气候变化的响应模式，取决于遗传变异及其在物种内部与物种间的分布格局。精准界定物种并量化其应对热胁迫的生理潜力，是开展相关研究的关键初始步骤。隐存种（cryptic species）指形态相似但遗传特征显著分化的类群，其对气候变化的生理响应可能存在显著差异。受气候变化严重影响的加勒比海优势造礁物种之一为山形星珊瑚（Orbicella faveolata）。此前Dziedzic等（2019）针对该物种的单个种群开展研究，报道了其热胁迫响应中的数量遗传变异，据此推测种群内的遗传变异可帮助这类珊瑚适应海洋温度上升。我们对该团队的原始数据进行了重新分析，结果发现该类群存在多个隐存演化支系，而非单一的泛交种群；其中一个演化支系并不具备耐热性。尽管不同隐存演化支系在部分区域存在共现现象，但至少有一个演化支系仅分布于单个地理区域。我们在受威胁物种中发现隐藏演化支系的研究结果，凸显了这些独立演化类群所面临的灭绝风险存在异质性——尤其值得关注的是，在海洋温度持续升高的背景下，仅部分类群具备存活的前景。