Genetic Variation in Widely Distributed Deep-Sea Molluscs: The Role of Oceanographic & Topographic Features

深海是地球上最大、最鲜为人知的生态系统。最近的探索揭示了一个令人惊讶的变化和动态的环境，以及在社区和景观层面上出人意料的高生物多样性。虽然生态模式的图景正在浮现，但这种丰富且高度地方性的动物的进化起源尚不清楚。这代表了我们对基本进化现象的理解上的巨大差距，并提出了一些重大的理论挑战。在其他环境中进化分化的主要证据是遗传种群结构。我们的第一笔资金用于开发从保存的深海软体动物中提取线粒体DNA的分子方法。这些新的方法进展的成功使我们能够在北美盆地内沿完整的深度梯度(119,000米)进行遗传分化分析。这些结果首次清楚地洞察了遗传变异如何以及在哪里积累和分化，从而产生了在深海中观察到的极高的生物多样性。遗传模式证实了深海种群中种群分化的唯一明确模型(Etter和Rex，1990年)。通过对保存下来的深海标本进行DNA测序的能力，首次有可能通过使用大量存档的深海材料来探索这一独特动物历史进化发展的许多方面。我们建议继续这项研究，从两个方向展开。首先，在几个物种中采样的16S mtDNA单倍型出人意料地大量突变，虽然令人兴奋，但可能会混淆对种群水平过程的解释，因为它不能归因于种内和种间的差异(例如，神秘的形态种)。我们建议开发从福尔马林固定的组织中检测单拷贝核基因的技术。基于核DNA的系统发育可以与来自mtDNA的系统发育进行比较，使我们能够区分大规模种内多态的假说和共存的深海类群分支的替代假说。当代基因流动有限。我们将针对rRNA簇的内部转录间隔区(ITS)区域以及蛋白质编码区中的内含子，因为它们的进化速度相对较快。处理福尔马林固定组织中的核DNA比我们在mtDNA位点上的成功更具挑战性，主要是因为基因组拷贝数/细胞的差异。然而，我们在两个基因座上的初步成功将表明，对那些先前具有mtDNA特征的个体进行核基因分析是可行的。拟议的研究对于自信地解释我们在盆地内的结果是必不可少的，允许开发在更大规模上解释模式所需的分子工具，并为阐明深海协调的演化过程提供了对几个独立地点的分析的力量。其次，我们建议将遗传种群结构的分析扩展到我们在区域尺度上成功分析的五个物种的海洋尺度上，并测试特定的潜在隔离障碍是否会影响种群结构。像许多深海生物一样，这些物种分布非常广泛。要完全了解种群分化、物种形成和高等类群的适应性辐射，显然需要在非常大的尺度上分析地理变异，包括那些可能存在地理隔离障碍的区域。潜在的障碍包括距离、深度、主要地形特征和洋流模式。我们将通过比较两种不同扩散模式的腹足类的遗传结构，来研究隔离屏障在大规模种群结构中的重要性，这两种遗传结构应该以非常不同的方式响应洋流和海底地形的隔离效应。一个物种在表层洋流中以浮游营养的方式发展，另一个物种在深海洋流中以磷营养的方式发展。将使用统计模型来确定是否可以通过盆地内部和之间的深度和距离的差异来预测遗传距离，并与潜在的隔离障碍相对应。双壳类大规模的遗传种群结构将有助于我们对深海物种形成的理解，并检验我们目前研究中发现的种群间遗传距离随着深度的增加而减小的趋势的普遍性。这项研究是第一次在全海洋范围内对物种进行对照比较，有可能揭示深海生态系统在与所涉过程相适应的尺度上进化差异的基本原因。扩大我们对区域差异的分析，将超大规模隔离障碍的影响包括在内，将是我们对深海进化动力学的重大进步，并将为今后提出关于深海生物多样性起源的问题提供必要的信息。A 1。

The deep sea is the largest and least known ecosystem on Earth. Recent exploration has revealed a surprisingly varied and dynamic environment, and quite unexpectedly high biodiversity at both community and landscape levels. While a picture of ecological patterns is emerging, the evolutionary origin of this rich and highly endemic fauna is unknown. This represents a huge gap in our understanding of basic evolutionary phenomena and presents a number of major theoretical challenges. The primary evidence of evolutionary divergence in other environments is genetic population structure. Our first grant was devoted to developing molecular methods to extract n dtochondrial DNA from preserved deep sea molluscs. The success of these new methodological advances enabled us to perform an analysis of genetic differentiation along a complete depth gradient (119 5000 m) within the North American Basin. Results provide the first clear insight into how and where genetic variation accumulates and differentiates to produce the enormously high biodiversity observed in the deep ocean. Genetic patterns confirmed the only explicit model of population differentiation in deep sea populations (Etter and Rex 1990). The ability to sequence DNA in preserved deep sea specimens makes it possible to explore, for the first time, many facets of the historical evolutionary development of this unique fauna by using the vast archived collections of deep sea material. We propose to continue this research by expanding in 2 directions. First, the unexpectedly large number of mutations characterizing 16S mtDNA haplotypes sampled in several species, while exciting, can confound interpretations of population level processes because it cannot be ascribed to intraspecific versus interspecific divergence (e.g., cryptic morphospecies). We propose to develop techniques to assay single copy nuclear genes from formalin fixed tissues. Phylogenies based on nuclear DNA can be compared to those from the mtDNA enabling us to distinguish between the hypotheses of large scale intraspecific polymorphism versus the alternative of co existing 'clades' of deep sea taxa. with limited contemporary gene flow. We will target the internally transcribed spacer (ITS) regions of the rRNA cluster as well as introns within protein coding regions because of their relatively rapid rate of evolution. Working with the nuclear DNA from formalin fixed tissues is more challenging than our successes with mtDNA loci, primarily due to differences in genome copy number/cell. However, our preliminary success with two loci would indicate that nuclear gene assays from those individuals previously characterized for mtDNA are feasible. The proposed research is essential to the confident interpretation of our within basin results, allows for the development of molecular tools necessary for interpreting patterns at larger scales, and provides the strength of an analysis of several independent loci for elucidating concordant evolutionary processes in the deep sea. Second, we propose to extend the analysis of genetic population structure to ocean wide scales in five species that we have successfully analyzed on a regional scale and to test whether specific potential isolating barriers influence population structure. Like many deep sea organisms, these species are very widely distributed. A complete understanding of population differentiation, species formation and adaptive radiation of higher taxa clearly requires analysis of geographic variation on very large scales including those on which geographic isolating barriers may operate. Potential barriers include distance, depth, major topographic features and ocean current patterns. We will investigate the importance of isolating barriers on large scale population structure by comparing the genetic structure of two gastropods with different modes of dispersal, which should respond to the isolating effects of currents and bottom topography in very different ways. One species develops planktotrophically in the surface currents and the other has lecithotrophic development in abyssal currents. Statistical models will be used to determine whether genetic distance can be predicted by differences in depth and distance within and among basins, and corresponds to potential isolating barriers. Large scale genetic population structure in bivalves will contribute significantly to our understanding of speciation in the deep sea, and test the generality of the trend discovered in our current research that interpopulation genetic distance decreases with increasing depth. This research is the first oceanwide controlled comparison of species that has the potential to reveal the basic causes of evolutionary divergence in the deep sea ecosystems on scales that are appropriate to the processes involved. Expanding our analysis of regional differentiation to include the effects of isolating barriers on very large scales would be a major advance in our understanding of evolutionary dynamics in the deep sea and will provide essential information to formulate future questions about the origin of deep sea biodiversity. A 1.