Ecological constraints on phenotypic evolution: a case study with Lake Malawi's 'prototype' cichlid fish

表型进化的生态限制：马拉维湖“原型”丽鱼科鱼的案例研究

• 批准号: NE/H018115/1
• 负责人: Martin Genner
• 金额: $ 9.34万
• 依托单位: University of Bristol
• 依托单位国家: 英国
• 项目类别: Training Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FH018115%2F1
• 关键词: Ecological; constraints; phenotypic; evolution; case

By studying 'model systems' we are gaining a better understanding of how biological diversity has evolved and is maintained by sexual and natural selection. However, we know little about why evolution of new species takes place in some environments, but fails in others. For example, many fishes have evolved new forms in lakes, but not in rivers, including sticklebacks, trout, perches and catfishes. Understanding this may help us to know how environments mediate the type of evolution that takes place, and address how future environmental changes, for example in frequency of extreme events and presence of alien species, may change evolutionary pathways. The type of process that mediates population size influences the strength of competition among offspring, and decides which individuals eventually get to mate. If populations are limited by space or food, then competition between members of the population will be strong, and it should pay to produce young that are good competitors for that environment, leading to the evolution of locally specialised fish. In such habitats it would not necessarily pay to disperse to locations where these specialisations are less effective. If populations are limited by occasional catastrophic events, such as droughts, selection will favour generalists that take opportunities as and when they arise. In these habitats selection may favour evolution of high dispersal, to prevent females losing all offspring should unfavourable conditions arise. In Lake Malawi hundreds of cichlid fish species have evolved in the lake, but this has not happened in surrounding rivers, but we have no clear explanation for why. The proposed research will explore if the types of selection imposed by contrasting environments have influenced patterns and rates of evolution. The work will study the only fish in the Malawi cichlid radiation that is present in both rivers and the lake, Astatotilapia calliptera (=the 'prototype'), a species with functional morphological differences (tooth, jaw) between populations. The studentship will involve four components: 1) field surveys to test if river and lake cichlid population sizes are controlled differently, with river fish populations being subject to annual catastrophic events, while lake fish are stable over long periods of time and controlled by food and space availability. 2) an analysis of dispersal of river and lake populations, by quantifying gene flow using genetic (microsatellite) markers. 3) an analysis of morphological and ecological specialisation in river and lake populations. This will involve collecting fish in the field and measuring functional traits. To test if differences are a consequence of selection, fish from four populations will be reared in a common garden experiment in laboratory aquaria, enabling quantification of the extent of variation that is explained by underlying genetic differences. 4) A study of evolutionary relationships of populations using genetic (AFLP) markers, enabling tests of whether the same morphology has evolved only once, or perhaps multiple times in parallel. Together this information will: a) help explain why new species evolve in some environments, but not in others; b) contribute to the development of a model system for studying how environmental variability influences evolution; c) help explain patterns of biodiversity over regional spatial scales, and d) help determine how evolutionary processes may be altered by modern environmental changes. The skills, experience and enthusiasm of three relatively newly appointed academics of the University of Bristol and the Natural History Museum will provide a positive learning environment for the student. In addition to generic training in scientific expertise that will be provided, specific training will be gained in numerous skills, including tropical fieldwork, quantitative morphology, ecological surveys, population genetics, experimental ecology and molecular phylogenetics.

通过研究“模式系统”，我们正在更好地理解生物多样性是如何通过性选择和自然选择来进化和维持的。然而，我们对为什么新物种的进化在一些环境中发生，而在另一些环境中却失败了，我们知之甚少。例如，许多鱼类在湖泊中进化出了新的形态，但在河流中却没有，包括刺鱼、鲑鱼、鲈鱼和叉尾鱼。了解这一点可能有助于我们了解环境如何调节发生的进化类型，并解决未来环境变化可能如何改变进化路径，例如极端事件的频率和外来物种的存在。调节种群大小的过程类型会影响后代之间的竞争强度，并决定最终哪些个体会交配。如果种群受到空间或食物的限制，那么种群成员之间的竞争将是激烈的，培育出对该环境具有良好竞争能力的幼鱼应该是值得的，从而导致当地专门化鱼类的进化。在这样的栖息地，分散到这些专门化效果较差的地方并不一定会有好处。如果人口受到偶尔发生的灾难性事件(如干旱)的限制，那么选择将有利于那些在机会出现时抓住机会的多面手。在这些栖息地，选择可能有利于高度分散的进化，以防止雌性在不利条件出现时失去所有后代。在马拉维湖，数百种慈鱼在湖里进化，但这并没有发生在周围的河流中，但我们没有明确的解释为什么。这项拟议的研究将探索由对比环境强加的选择类型是否影响了进化的模式和速度。这项工作将研究马拉维慈济鱼辐射中唯一存在于河流和湖泊中的鱼类--拟罗非鱼，这是一种在不同种群之间具有功能形态差异(牙齿、颌骨)的物种。学生学习将包括四个部分：1)实地调查，以测试河流和湖泊池鱼种群数量是否受到不同的控制，河流鱼类种群受到年度灾难性事件的影响，而湖泊鱼类种群长期稳定，并受食物和空间供应的控制。2)通过使用遗传(微卫星)标记量化基因流，分析河流和湖泊种群的扩散。3)河流和湖泊种群的形态和生态专化性分析。这将涉及到在野外采集鱼类和测量功能特征。为了测试差异是否是选择的结果，来自四个种群的鱼将在实验室水族箱的普通花园实验中饲养，从而能够量化潜在遗传差异所解释的差异程度。4)使用遗传(AFLP)标记研究种群的进化关系，从而能够测试相同的形态是否只进化了一次，或者可能并行进化了多次。这些信息将有助于：a)有助于解释为什么新物种在某些环境中进化，而不是在其他环境中；b)有助于开发研究环境变异性如何影响进化的模型系统；c)有助于解释生物多样性在区域空间尺度上的格局；以及d)有助于确定现代环境变化可能如何改变进化过程。布里斯托尔大学和自然历史博物馆三位相对较新上任的学者的技能、经验和热情将为学生提供积极的学习环境。除了将提供的科学专门知识的一般性培训外，还将获得许多技能方面的具体培训，包括热带田野调查、数量形态学、生态调查、种群遗传学、实验生态学和分子系统学。