Bleaching causes loss of disease resistance within the threatened coral species Acropora cervicornis.
Bleaching causes loss of disease resistance within the threatened coral species Acropora cervicornis.
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DOI：
10.7554/elife.35066
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发表时间：
2018-09-11
期刊：
影响因子：
7.7
通讯作者：
Baums IB
中科院分区：
文献类型：
--
作者：
Muller EM;Bartels E;Baums IB
随着海洋变暖和珊瑚数量减少，迫切需要确定造礁珊瑚等基础物种的适应潜力。理论预测，珊瑚可能通过对现有遗传变异的选择来适应气候变化。然而，珊瑚不仅面临着不断上升的温度，还面临着新的疾病。我们研究了两个主要的压力，影响受威胁的珊瑚，鹿角珊瑚的殖民地之间的相互作用：白带病和高水温。我们确定27%的A.在温度异常之前，颈角牛是抗病的。然而，由于珊瑚宿主受损或致病剂量/毒力增加，在漂白事件中，抗病能力基本丧失。抗病性和耐温性之间不存在平衡，感病性与共生藻菌株无关。目前的研究表明，对温度胁迫的敏感性增加了疾病相关死亡率的风险，只有少数基因可能在高温下保持或获得传染病抗性。我们的结论是A.在下佛罗里达礁岛群中，几乎没有既能抵抗变暖又能抵抗疾病的基因型。鹿角珊瑚曾经在整个佛罗里达珊瑚礁区盛行。然而，过去几十年来，由于疾病爆发和海洋温度上升，珊瑚数量大幅减少。鹿角珊瑚没有显示出自然恢复的迹象，因此一直是佛罗里达大部分地区恢复工作的重点。为什么要把时间和精力花在种植那些不太可能在持续恶化的环境条件下生存的珊瑚上呢？原因之一是某些珊瑚的基因组成-基因型-使它们对某些威胁更具弹性。然而，可能存在与这些弹性特征相关的权衡。例如，珊瑚可能能够忍受高温，但可能很容易屈服于疾病。先前的研究已经确定了一些鹿角珊瑚基因型，它们对一种称为白带病的感染有抵抗力。高水温对珊瑚抵抗这种疾病的能力的影响尚不清楚。还有一种可能性是，更多种类的珊瑚可能表现出类似的抗病能力。为了研究，Muller等人进行了两个实验，在珊瑚漂白事件之前和期间将鹿角珊瑚基因型暴露于白色带病变组织。大约25%的鹿角测试的人口是抗白带病之前的漂白事件。当珊瑚在漂白过程中暴露于白色带疾病时，两倍的珊瑚死亡。15种基因型珊瑚中有2种，即13%，即使在漂白的情况下也能抵抗这种疾病。此外，珊瑚基因型内的漂白水平与它们患上白带病的容易程度无关，这表明耐热性和抗病性之间没有直接的权衡。这些结果表明，有非常哈代珊瑚，创造的性质，已经存在。将这些特征仔细纳入珊瑚恢复计划可能会增加基于人口的恢复的可能性。据估计，佛罗里达珊瑚礁区对该州经济的价值超过60亿美元，提供了7万多个就业机会，每年吸引数百万游客进入佛罗里达。然而，如果珊瑚礁区域内的活珊瑚得不到恢复，这些生态系统服务将大部分丧失。Muller等人提出的结果强调，在恢复珊瑚时，需要保持高遗传多样性，同时增加恢复力。他们还强调，抗病珊瑚，即使漂白，已经存在，并可能是一个不可分割的一部分，恢复佛罗里达的珊瑚礁区。
Determining the adaptive potential of foundation species, such as reef-building corals, is urgent as the oceans warm and coral populations decline. Theory predicts that corals may adapt to climate change via selection on standing genetic variation. Yet, corals face not only rising temperatures but also novel diseases. We studied the interaction between two major stressors affecting colonies of the threatened coral, Acropora cervicornis: white-band disease and high water temperature. We determined that 27% of A. cervicornis were disease resistant prior to a thermal anomaly. However, disease resistance was largely lost during a bleaching event because of more compromised coral hosts or increased pathogenic dose/virulence. There was no tradeoff between disease resistance and temperature tolerance; disease susceptibility was independent of Symbiodinium strain. The present study shows that susceptibility to temperature stress creates an increased risk in disease-associated mortality, and only rare genets may maintain or gain infectious disease resistance under high temperature. We conclude that A. cervicornis populations in the lower Florida Keys harbor few existing genotypes that are resistant to both warming and disease. The staghorn coral was once prevalent throughout the Florida Reef Tract. However, the last few decades have seen a substantial reduction in the coral population because of disease outbreaks and increasing ocean temperatures. The staghorn coral shows no evidence of natural recovery, and so has been the focus of restoration efforts throughout much of the Florida region. Why put the time and effort into growing corals that are unlikely to survive within environmental conditions that continue to deteriorate? One reason is that the genetic make-up – the genotype – of some corals makes them more resilient to certain threats. However, there could be tradeoffs associated with these resilient traits. For example, a coral may be able to tolerate heat, but may easily succumb to disease. Previous studies have identified some staghorn coral genotypes that are resistant to an infection called white-band disease. The influence of high water temperatures on the ability of the coral to resist this disease was not known. There also remained the possibility that more varieties of coral might show similar disease resistance. To investigate Muller et al. conducted two experiments exposing staghorn coral genotypes to white-band diseased tissue before and during a coral bleaching event. Approximately 25% of the population of staghorn tested was resistant to white-band disease before the bleaching event. When the corals were exposed to white-band disease during bleaching, twice as much of the coral died. Two out of the 15, or 13%, of the coral genotypes tested were resistant to the disease even while bleached. Additionally, the level of bleaching within the coral genotypes was not related to how easily they developed white-band disease, suggesting that there are no direct tradeoffs between heat tolerance and disease resistance. These results suggest that there are very hardy corals, created by nature, already in existence. Incorporating these traits thoughtfully into coral restoration plans may increase the likelihood of population-based recovery. The Florida Reef Tract is estimated to be worth over six billion dollars to the state economy, providing over 70,000 jobs and attracting millions of tourists into Florida each year. However, much of these ecosystem services will be lost if living coral is not restored within the reef tract. The results presented by Muller et al. emphasize the need for maintaining high genetic diversity while increasing resiliency when restoring coral. They also emphasize that disease resistant corals, even when bleached, already exist and may be an integral part of the recovery of Florida’s reef tract.