Collaborative research: ENSO-enhanced gene flow across the Eastern Pacific Barrier

珊瑚礁构成了世界上物种最丰富的海洋生态系统，但人为变化威胁着它们的健康，并危及依赖它们的经济。生活在东太平洋的珊瑚种群尤其不稳定，因为它们生活在一个环境条件已经决定了边缘生存的地区，它们与其他太平洋珊瑚礁珊瑚之间隔着5000-8000公里不适合居住的深水(东太平洋屏障，EPB)。管理这些珊瑚需要了解哪些种群有共同的进化史，以及目前扩散如何将种群联系在一起。缺乏这种信息是因为1)经常用于推断种群关系的线粒体DNA标记已被证明在珊瑚物种内是不变的，因此没有信息量，以及2)基于等位基因频率数据的遗传分析估计了平均数千代的迁徙，这可能不能反映目前的种群连接模式。最近厄尔尼诺南方涛动(ENSO)事件强度的增加可能改变了过去几代人的种群间扩散模式。这样的ENSO事件使从繁茂的中太平洋珊瑚礁到东太平洋的繁殖物向东传输的时间减半。该项目将采用基因技术的组合来确定1)东太平洋珊瑚种群何时与中太平洋珊瑚种群分化，2)这些地区的今天珊瑚种群如何通过扩散联系在一起，3)最近由ENSO事件引起的洋流变化是否改变了这些交换模式。这项工作成功的关键将是应用新的遗传分析，旨在识别最近才被隔离的种群群体(20代)，并能够揭示过去种群规模的变化。这项工作将集中在太平洋主要的珊瑚礁建造商Porites lobata上。约40人的样本将从横跨环保局的12个地点中的每个地点进行。通过将单系和副系基因谱系的分布与模型化的预期进行比较，并通过使用合并分析，将对分歧时间的替代假设进行评估。来自15个单拷贝基因座的核基因序列(从随机抽样的cDNA文库中获得)将被用于这一目的。微卫星基因座(每个物种12-15个)将提供多个基因座基因类型，用于输入基于模型的聚类和分配程序。这些遗传分析将提供目前迁徙如何将中太平洋和东太平洋珊瑚连接起来的图景，以及ENSO事件的变化是否以及如何改变了这些模式。将在这里收集的遗传数据将为管理许多人赖以生存的自然资源提供关键信息。这项拟议的研究将为一所为少数民族人口众多的地区服务的机构的本科生和研究生提供培训机会。

Coral reefs constitute the world's most-species-rich marine ecosystems, but anthropogenic changes threaten their health and jeopardize economies that depend on them. Populations of corals living in the eastern Pacific Ocean are especially precarious, as they inhabit a region where environmental conditions already dictate a marginal existence and they are isolated from other Pacific reef corals by 5000-8000 km of uninhabitable deep water (the Eastern Pacific Barrier, EPB). Managing these corals requires knowledge of which populations share common evolutionary histories and how dispersal presently links populations. This information has gone lacking because 1) the mitochondrial DNA markers often used to infer population relationships have proven invariant within coral species and thus uninformative, and 2) genetic analyses based on allele frequency data estimate migration averaged over thousands of generations, which may not reflect present patterns of population connectivity. Recent increases in the intensity of El-Nino Southern Oscillation (ENSO) events may have altered patterns of inter-population dispersal over the last few generations. Such ENSO events halve the eastward transport time of propagules traveling from luxuriant central Pacific coral reefs to the eastern Pacific. This project will employ a combination of genetic techniques to determine 1) when populations of corals in the eastern Pacific diverged from those in the central Pacific, 2) how present-day coral populations in these regions are linked by dispersal, and 3) whether recent changes in currents caused by ENSO events have altered these patterns of exchange. Critical to the success of the work will be the application of new genetic analyses designed to recognize groups of populations that have been isolated only very recently (20 generations) and can reveal past changes in population sizes. The work will focus on a major Pacific reef builder, Porites lobata. Samples of about 40 individuals will be made from each of 12 localities spanning the EPB. Alternative hypotheses for divergence times will be evaluated by comparing the distribution of monophyletic and paraphyletic gene genealogies to modeled expectations and by using coalescent analyses. Nuclear gene sequences from 15 single copy loci (obtained from random sampling of cDNA libraries) will be used for this purpose. Microsatellite loci (12-15 per species) will provide multi-locus genotypes for input into model-based clustering and assignment programs. These genetic analyses will provide a picture of how migration presently connects central and eastern Pacific corals and whether and how changes in ENSO events have altered these patterns. The genetic data to be gathered here will provide critical information for managing a natural resource upon which many people depend. The proposed research will provide training opportunities to undergraduate and graduate students at an institution that serves a region with a large minority population.