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

珊瑚礁是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危险，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被5000-8000公里的不适宜居住的深水（东太平洋屏障，EPB）隔离开来。管理这些珊瑚需要了解哪些种群具有共同的进化历史，以及目前分散如何将种群联系起来。这些信息之所以缺乏，是因为1)通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中是不变的，因此信息不足；2)基于等位基因频率数据的遗传分析估计了数千代的平均迁移，这可能无法反映当前的种群连接模式。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种群间分散的模式。这种ENSO事件使繁殖体从繁茂的中太平洋珊瑚礁向东传播到东太平洋的时间减半。该项目将采用多种遗传技术来确定：1)东太平洋的珊瑚种群何时与太平洋中部的珊瑚种群分化；2)这些地区的珊瑚种群是如何通过分散联系在一起的；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（20代）分离的种群，并能揭示过去种群规模的变化。这项工作将集中在一个主要的太平洋珊瑚礁建造者，波蒂斯洛巴塔。大约40个个体的样本将从横跨EPB的12个地点的每个地点采集。通过将单系和副系基因谱系的分布与模型期望进行比较，并通过使用聚结分析，将对分化时间的其他假设进行评估。来自15个单拷贝位点的核基因序列（从cDNA文库随机取样获得）将用于此目的。微卫星位点（每个物种12-15个）将为基于模型的聚类和分配程序提供多位点基因型。这些基因分析将提供一幅图，说明目前太平洋中部和东部珊瑚的迁移是如何联系起来的，以及ENSO事件的变化是否以及如何改变了这些模式。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。拟议中的研究将为一所大学的本科生和研究生提供培训机会，该大学为少数民族人口众多的地区提供服务。

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.