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，后者会引发珊瑚白化并造成珊瑚死亡。珊瑚礁对气候变化的响应方式，将取决于遗传变异及其在物种内部与物种间的分布格局。一项关键的初步研究步骤是精准界定物种，并量化其应对热胁迫的生理潜能。隐存种（cryptic species）是指形态相似但遗传分化显著的类群，它们对气候变化的生理响应可能存在差异。受气候变化严重影响的加勒比海优势造礁珊瑚之一为山状星珊瑚（*Orbicella faveolata*）。此前Dziedzic等人（2019）在该物种的单个种群中报道了其应对热胁迫的生理响应存在数量遗传变异，这表明种群内的遗传变异可帮助这些珊瑚适应海洋温度上升。我们对其研究数据进行了重新分析，结果发现该类群存在多个隐存谱系，而非单一的泛交种群，其中一个谱系并不具备耐热性。尽管不同隐存谱系在部分区域存在共现现象，但至少有一个谱系仅分布于单一地理位置。我们在这一受威胁物种中发现隐藏谱系的研究结果，凸显出这些独立演化类群所面临的灭绝风险存在差异——尤其当暖化海洋环境下仅部分类群的生存前景看似乐观时，这种风险差异尤为显著。