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

广泛分布的深海软体动物的遗传变异：海洋学的作用

• 批准号: 9811925
• 负责人: Ron Etter
• 金额: $ 23.93万
• 依托单位: University of Massachusetts Boston
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1998
• 资助国家: 美国
• 起止时间: 1998-10-01 至 2001-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9811925&HistoricalAwards=false
• 关键词: Genetic; Variation; Widely; Distributed; Deep

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.

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，但这种丰富且高度特有的动物群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存在巨大差距，并提出了一些重大的理论挑战。在其他环境中进化分歧的主要证据是遗传种群结构。我们的第一笔赠款用于开发从保存的深海软体动物中提取昆虫DNA的分子方法。这些新的方法进步的成功，使我们能够进行遗传分化的分析沿着一个完整的深度梯度（119 - 5000米）内的北美盆地。研究结果首次清晰地揭示了遗传变异是如何以及在何处积累和分化的，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唯一明确的种群分化模式（Etter和雷克斯，1990年）。对保存的深海标本进行DNA测序的能力，使人们有可能利用大量的深海材料档案，首次探索这一独特动物群历史进化发展的许多方面。我们建议通过向两个方向扩展来继续这项研究。 首先，在几个物种中取样的16 S mtDNA单倍型的突变数量出乎意料地多，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与种间的分歧（例如，隐蔽形态种）。我们建议开发技术，以测定单拷贝核基因福尔马林固定的组织。基于核DNA的系统发育可以与mtDNA的系统发育进行比较，使我们能够区分大规模种内多态性的假设与深海类群共存的“分支”的替代。当代基因流有限的情况下我们将针对rRNA簇的内转录间隔区（ITS）以及蛋白质编码区内的内含子，因为它们的进化速度相对较快。使用福尔马林固定组织的核DNA比我们使用mtDNA基因座的成功更具挑战性，主要是由于基因组拷贝数/细胞的差异。然而，我们在两个位点上的初步成功表明，对先前以mtDNA为特征的个体进行核基因检测是可行的。拟议的研究对于自信地解释我们的盆地内结果至关重要，可以开发更大规模解释模式所需的分子工具，并为阐明深海中一致的进化过程提供多个独立基因座分析的力量。 其次，我们建议扩展到海洋的广泛尺度上，我们已经成功地分析了在区域范围内的五个物种的遗传种群结构的分析，并测试是否特定的潜在隔离障碍影响人口结构。像许多深海生物一样，这些物种分布非常广泛。一个完整的理解人口分化，物种形成和适应性辐射的高等类群显然需要分析地理变异非常大的规模，包括那些地理隔离障碍可能会运作。潜在的障碍包括距离、深度、主要地形特征和洋流模式。我们将调查隔离障碍的重要性，大规模的人口结构，通过比较两种腹足类的遗传结构与不同的传播模式，这应该响应隔离效果的电流和底部地形在非常不同的方式。一个物种在表层海流中以营养方式发育，另一个物种在深海海流中以营养方式发育。将使用统计模型来确定是否可以通过盆地内部和盆地之间的深度和距离差异来预测遗传距离，并与潜在的隔离屏障相对应。大规模的遗传种群结构的双壳类将有助于我们在深海物种形成的理解，并测试在我们目前的研究中发现的趋势，种群间遗传距离随着深度的增加而减少的普遍性。这项研究是第一次在全海洋范围内对物种进行受控比较，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分歧的基本原因。将我们对区域差异的分析扩大到包括大规模隔离障碍的影响，将是我们对深海进化动力学理解的一个重大进步，并将为今后提出有关深海生物多样性起源的问题提供必要的信息。 的1.