Evolution of Deep Sea Molluscs II

深海动物种群分化和物种形成的第一个明确模型——深度分化假说是在20世纪90年代初提出的。根据这一理论，种群分化的潜力随着深度的增加而降低，因为与更广泛和环境均匀的深海平原（4000米）相比，深海带（200- 4000米）具有更强的选择梯度和更多的地理隔离机会来阻碍基因流动。为了确定与深度相关的变异是否是遗传的，也就是进化变化的结果，PI开发了新的方法，从早期探险中收集的深海软体动物物种中提取线粒体DNA并进行测序，这些物种被固定在福尔马林中并保存在酒精中。这些初步研究支持了深度分化假说。他们还揭示了使用保存材料的局限性。对于这个项目，PI描述了从以前的工作中出现的关于深海进化的两个假设：1)深度分化假设表明种群差异随着深度而减小；2) 3300 m处种群结构的断裂可能是未被认识到的系统地理屏障。PI将使用深海原分支双壳类动物和最近开发的统计系统地理和系统发育模型，用多个独立的基因座来测试这些假设。上述工作依赖于福尔马林固定的组织，限制了对单个位点（mtDNA）的分析。核位点作为种群结构、基因流动和历史影响的独立衡量标准是必不可少的，但对于确定PI记录的一些显著差异是否代表隐物种也是至关重要的。在上一轮资助中收集的新材料使PI能够开发必要的核位点并评估其对这项工作的效用。本建议的主要焦点是使用这些新的标记来测试这些假设，并区分种内与种间变异。知识价值：深海支持着最多样化和独特的海洋群落之一，其进化和历史发展几乎是未知的。拟议的研究将对回答在这个广阔而遥远的环境中进化多样化的两个最基本的问题做出非常重要的贡献：它发生在哪里，如何发生？对半齿藻（Deminucula atacellana）强烈的水深差异的分析，将提供对深海生物潜在的早期物种形成（除了减少环境）的第一次详细调查，并可能确定所涉及的规模和机制。它还将为未来深海进化研究创造一个坚实的概念和方法背景，并为理解更大尺度（例如，在海洋盆地或泛大西洋之间）的水深和地理变化奠定基础。更广泛的影响：该研究项目将培训本科生、研究生和公立学校教师。在马萨诸塞大学波士顿分校，学生和教师有很好的机会直接参与各级科学教育和公共宣传。目前，生物系拥有美国国家科学基金会的本科生研究经验项目、美国国立卫生研究院最大限度地提高学生多样性（IMSD）项目、通往学士学位的桥梁项目和美国国家科学基金会环境生物学本科生指导项目。所有这些项目都面向代表性不足的少数民族，来自这些项目的学生已经并将继续参与PI的研究。该校园拥有波士顿科学伙伴关系基金，用于升级高中科学课程，并且是海洋科学教育卓越中心，以培养公众对海洋科学的认识。PI将招募本科生、研究生和教师参与该研究项目，深海生物学的主题将被纳入大学和高中课程。该研究对深海生态系统的保护和可持续发展也具有广泛的意义。种群遗传结构是生物多样性的重要组成部分，对深海生物资源开发造成的物种灭绝具有重要意义。

The first explicit model of population differentiation and speciation in the deep-sea fauna, the depth-differentiation hypothesis, was formulated in the early 1990s. According to this theory, the potential for population differentiation decreases with depth because the bathyal zone (200- 4000 m) has stronger selective gradients and more opportunity for geographic isolation to impede gene flow than does the more extensive and environmentally uniform abyssal plain (4000 m). To determine whether depth-related variation is genetic, and therefore a consequence of evolutionary change, the PI has developed new methods to extract and sequence mitochondrial DNA from archived deep-sea molluscan species collected in earlier expeditions that had been fixed in formalin and preserved in alcohol. These preliminary studies supported the depth-differentiation hypothesis. They also revealed the limitations of using preserved material. For this project, the PI describes 2 hypotheses about evolution in the deep sea that emerged from the previous work: 1) The depth differentiation hypothesis suggests population divergence decreases with depth; and 2) A strong break in population structure at 3300 m might represent an unrecognized phylogeographic barrier. The PI will test each of these hypotheses with multiple independent loci using deep-sea protobranch bivalves and recently developed statistical phylogeographic and phylogenetic models. The aforementioned work relied on formalin-fixed tissues, restricting analyses to a single locus (mtDNA). Nuclear loci are essential as independent measures of population structure, gene flow and historical influences, but are also critical to establish whether some of the remarkable divergences the PI documented represent cryptic species. The new material collected during the previous round of funding allowed the PI to develop the necessary nuclear loci and assess their utility for this work. The primary focus of this proposal is to use these new markers to test each of these hypotheses and distinguish intra- versus inter-specific variation. Intellectual Merit: The deep-sea supports one of the most diverse and unique marine communities, the evolutionary and historical development of which is virtually unknown. The proposed research will contribute very significantly to answering the two most basic questions about evolutionary diversification in this vast and remote environment: Where does it occur, and how? Analysis of the strong bathymetric divergence in Deminucula atacellana will provide the first detailed investigation of potential incipient speciation in a deep-sea organism (apart from reducing environments) and possibly identify the scales and mechanisms involved. It will also create a solid conceptual and methodological context for future evolutionary studies in the deep sea and lay the groundwork for understanding bathymetric and geographic variation at much larger scales (e.g., among ocean basins or pan-Atlantic). Broader Impacts: The research program will train undergraduate and graduate students and public school teachers. At UMass-Boston, students and faculty have outstanding opportunities to be directly involved in science education and public outreach at all levels. Currently, the biology Department has an NSF-Research Experiences for Undergraduate program, an NIH Initiative for Maximizing Student Diversity (IMSD) Program, a Bridges to Baccalaureate Program, and an NSF Undergraduate Mentoring in Environmental Biology program. All are oriented toward underrepresented minorities, and students from each of these initiatives have and will continue to be been involved in the PI's research. The campus has a Boston Science Partnership Grant to upgrade high school science curricula and is a Center of Ocean Science Education Excellence to foster public awareness of ocean science. The PI will recruit undergraduates, graduate students, and teachers into this research program, and topics in deep-sea biology will be incorporated into university and high school curricula. The research also has broad relevance for conservation and sustainable development of the deep-sea ecosystem. Genetic population structure is a crucial component of biodiversity, and has important implications for extinction potential from deep-sea exploitation.