Collaborative research: Is hybridization among threatened Caribbean coral species the key to their survival or the harbinger of their extinction?

合作研究：受威胁的加勒比珊瑚物种之间的杂交是它们生存的关键还是它们灭绝的预兆？

• 批准号: 1538469
• 负责人: Nicole Fogarty
• 金额: $ 39.19万
• 依托单位: Nova Southeastern University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-10-01 至 2019-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1538469&HistoricalAwards=false
• 关键词: Collaborative; research; hybridization; among; threatened

Reef-building acroporid corals form the foundation of shallow tropical coral communities throughout the Caribbean. Yet, the once dominant staghorn coral (Acropora cervicornis) and the elkhorn coral (A. palmata) have decreased by more than 90% since the 1980s, primarily from disease. Their continuing decline jeopardizes the ability of coral reefs to provide numerous societal and ecological benefits, including economic revenue from seafood harvesting and tourism and shoreline protection from extreme wave events caused by storms and hurricanes. Despite their protection under the U.S. Endangered Species Act since 2006, threats to the survival of reef-building acroporid corals remain pervasive and include disease and warming ocean temperatures that may lead to further large-scale mortality. However, hybridization among these closely related species is increasing and may provide an avenue for adaptation to a changing environment. While hybrids were rare in the past, they are now thriving in shallow habitats with extreme temperatures and irradiance and are expanding into the parental species habitats. Additional evidence suggests that the hybrid is more disease resistant than at least one of the parental species. Hybridization may therefore have the potential to rescue the threatened parental species from extinction through the transfer of adapted genes via hybrids mating with both parental species, but extensive gene flow may alter the evolutionary trajectory of the parental species and drive one or both to extinction. This collaborative project is to collect genetic and ecological data in order to understand the mechanisms underlying increasing hybrid abundance. The knowledge gained from this research will help facilitate more strategic management of coral populations under current and emerging threats to their survival. This project includes integrated research and educational opportunities for high school, undergraduate and graduate students, and a postdoctoral researcher. Students in the United States Virgin Islands will take part in coral spawning research and resource managers will receive training on acroporid reproduction to apply to coral restoration techniques. Current models predict the demise of reefs in the next 200 years due to increasing sea surface temperatures and ocean acidification. It is thus essential to identify habitats, taxa and evolutionary mechanisms that will allow some coral species to maintain their role as foundation fauna. Hybridization can provide an avenue for adaptation to changing conditions. Corals hybridize with some frequency and results may range from the introduction of a few alleles into existing parent species via introgression, to the birth of a new, perhaps better adapted genetic lineage. The only widely accepted coral hybrid system consists of the once dominant but now threatened Caribbean species, Acropora cervicornis and A. palmata. In the past, hybrid colonies originating from natural crosses between elkhorn and staghorn corals were rare, and evidence of hybrid reproduction was limited to infrequent matings with the staghorn coral. Recent field observations suggest that the hybrid is increasing and its ecological role is changing throughout the Caribbean. These hybrids appear to be less affected by the disease that led to the mass mortality of their parental species in recent decades. Hybrids are also found thriving in shallow habitats with high temperatures and irradiance suggesting they may be less susceptible to future warming scenarios. At the same time, they are expanding into the deeper parental species habitats. Preliminary genetic data indicate that hybrids are now mating with each other, demonstrating the potential for the formation of a new species. Further, hybrids appear to be capable of mating with both staghorn and elkhorn coral, perhaps leading to gene flow between the parent species via the hybrid. Research is proposed to address how the increase in hybridization and perhaps subsequent introgression will affect the current ecological role and the future evolutionary trajectory of Caribbean acroporids. Specifically, this collaborative project aims to answer the following questions: 1) What is the historic rate, direction, and degree of introgression across species ranges and genomes? Linkage block analysis based on genome-wide SNP genotyping across three replicate hybrid zones will answer this question. 2) What is the current extent and future potential of later generation hybrid formation? Morphometric and genetic analyses combined with in vitro fertilization assays will be used. 3) What mechanisms allow hybrids to thrive in hot, shallow waters? A series of manipulative in situ and ex situ experiments will determine whether biotic or abiotic factors favor hybrid survival in shallow waters. 4) Are hybrids more disease resistant than the parentals species? Disease transmission assays in reciprocal transplant experiments and histological analysis to determine the extent of disease will be conducted. A multidisciplinary approach will be taken that combines traditional and cutting edge technology to provide a detailed analysis of the evolutionary ecology of Caribbean corals.

造礁顶孔珊瑚构成了整个加勒比海浅层热带珊瑚群落的基础。然而，自 20 世纪 80 年代以来，曾经占主导地位的鹿角珊瑚 (Acropora cervicornis) 和鹿角珊瑚 (A. palmata) 数量已减少 90% 以上，主要原因是疾病。它们的持续衰退危及珊瑚礁提供众多社会和生态效益的能力，包括海鲜捕捞和旅游业带来的经济收入，以及保护海岸线免受风暴和飓风造成的极端波浪事件的影响。尽管自 2006 年以来它们受到美国濒危物种法案的保护，但造礁顶孔珊瑚的生存威胁仍然普遍存在，包括疾病和海洋温度升高，这些威胁可能导致进一步大规模死亡。然而，这些密切相关的物种之间的杂交正在增加，并可能为适应不断变化的环境提供途径。虽然杂交种在过去很罕见，但现在它们在具有极端温度和辐照度的浅层栖息地中繁衍生息，并且正在扩展到亲本物种的栖息地。其他证据表明，杂交种比至少一种亲本物种具有更强的抗病能力。因此，杂交可能有可能通过与两个亲本物种交配来转移适应基因，从而拯救受威胁的亲本物种免于灭绝，但广泛的基因流动可能会改变亲本物种的进化轨迹，并导致其中一种或两种物种灭绝。该合作项目旨在收集遗传和生态数据，以了解增加杂交丰度的机制。从这项研究中获得的知识将有助于在当前和新出现的生存威胁下促进对珊瑚种群进行更具战略性的管理。该项目包括为高中生、本科生和研究生以及博士后研究员提供综合研究和教育机会。美属维尔京群岛的学生将参加珊瑚产卵研究，资源管理人员将接受顶孔动物繁殖培训，以应用于珊瑚恢复技术。目前的模型预测，由于海面温度升高和海洋酸化，珊瑚礁将在未来 200 年内消亡。因此，有必要确定栖息地、分类群和进化机制，使一些珊瑚物种能够保持其作为基础动物群的作用。杂交可以提供适应不断变化的条件的途径。珊瑚以一定的频率杂交，其结果可能包括通过基因渗入将一些等位基因引入现有的亲本物种，到诞生一个新的、也许更适应的遗传谱系。唯一被广泛接受的珊瑚杂交系统由曾经占主导地位但现在受到威胁的加勒比物种、Acropora cervicornis 和 A. palmata 组成。过去，鹿角珊瑚和鹿角珊瑚自然杂交产生的杂交群体很少见，杂交繁殖的证据仅限于与鹿角珊瑚的罕见交配。最近的实地观察表明，整个加勒比地区的杂交品种正在增加，其生态作用正在发生变化。这些杂交品种似乎较少受到近几十年来导致其亲本物种大规模死亡的疾病的影响。杂交种还被发现在高温和辐照度较高的浅层栖息地中繁衍生息，这表明它们可能不太容易受到未来变暖情况的影响。与此同时，它们正在扩展到更深的亲本物种栖息地。初步遗传数据表明，杂交种现在正在相互交配，展示了形成新物种的潜力。此外，杂交种似乎能够与鹿角珊瑚和鹿角珊瑚交配，这可能会通过杂交种导致亲本物种之间的基因流动。拟议的研究旨在解决杂交的增加以及随后的基因渗入将如何影响加勒比顶孔虫当前的生态作用和未来的进化轨迹。具体来说，该合作项目旨在回答以下问题：1）跨物种范围和基因组的历史渗入率、方向和程度是多少？基于跨三个复制杂交区的全基因组 SNP 基因分型的连锁块分析将回答这个问题。 2）下一代混合形成的当前程度和未来潜力是什么？将使用形态测量和遗传分析与体外受精测定相结合。 3）什么机制可以让杂交鱼在炎热的浅水中茁壮成长？一系列操纵性的原位和异位实验将确定生物或非生物因素是否有利于浅水中的杂种生存。 4) 杂交种是否比亲本物种更具有抗病能力？将进行相互移植实验中的疾病传播测定和组织学分析以确定疾病的程度。将采取多学科方法，结合传统和尖端技术，对加勒比珊瑚的进化生态学进行详细分析。