Macroevolutionary patterns and processes in Neotropical freshwater fishes: cichlids as a model

新热带淡水鱼类的宏观进化模式和过程：慈鲷作为模型

• 批准号: RGPIN-2014-05374
• 负责人: LopezFernandez, Hernan
• 金额: $ 1.83万
• 依托单位: University of Toronto
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2017
• 资助国家: 加拿大
• 起止时间: 2017-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=632033
• 关键词: Macroevolutionary; patterns; processes; Neotropical; freshwater

South and Central America, known as the Neotropical region, have the highest freshwater fish diversity anywhere on the planet, exceeding 7000 species. Yet we know very little about the evolutionary processes that originated such incredible diversity. My students and I study the evolution of a common group of Neotropical freshwater fishes, the family Cichlidae, and use it as a model to understand the forces that have shaped the evolution of Neotropical freshwater fishes. Cichlids have adapted to live in nearly every environment of South and Central America by diversifying into a large variety of forms and ecological habits. We hypothesize that the diversity and ecological versatility of cichlids resulted from early expansions into new, available ecological resources such as food and habitats (ecological opportunity), originating distinct, ecologically specialized genera. Contrastingly, within most of those genera, species tend to be similar to each other, sharing both their morphology (like body size and shape) and their ecological preferences (including habitat and diet). This lack of diversity among species within genera may stem from the opposite of ecological opportunity, adaptive constraint. Once a lineage becomes an ecological specialist, it may not be able to survive under conditions too different from those to which it is specialized. This forces the evolutionary path of the specialist to remain close to a so-called “adaptive peak”, around which all ecological, morphological and physiological conditions favor its survival. If the evolutionary path moves too far away from the peak, the species cannot survive. In this project, we want to understand how ecological opportunity and adaptive constraint produce different evolutionary outcomes. We will do this by studying the major evolutionary lines (genera) of American cichlids, and by comparing two genera within the group: “pike cichlids” in the genus Crenicichla, and “dwarf cichlids” in the genus Apistogramma. Pike cichlids have diversified into remarkably different forms and ecological niches, while the dwarf cichlids share similar ecologies and morphologies. Although both genera have comparable numbers of species, pike cichlids may have diversified through ecological opportunity, whereas dwarf cichlids may be evolving under severe adaptive constraint. This provides a natural system to study how these two forces can generate diversity through different mechanisms. We will use hundreds of DNA sequences and the fossil record to reconstruct the evolutionary relationships (the family tree) and the when American cichlids, pike cichlids, and dwarf cichlids originated. We will then use the dated family trees as roadmaps to understand how and when different features of these fishes appeared in their evolutionary history. We will trace the speed and form of evolutionary change in morphology (feeding mechanisms, swimming attributes) and ecology of the different groups of cichlids. By comparing different groups of cichlids, we will learn how ecological opportunity and adaptive constraint contributed to the diversification of one the most diverse families of fishes in the Americas. Understanding how evolutionary forces shape biological diversity is also relevant for biologists working on conservation or trying to understand the long term effects of climate change or other environmental transformations. How species respond to environmental changes depends on how adaptable they are to varying ecological conditions. It follows that species belonging in groups with severe adaptive constraints may not be able to tolerate changes to their environment, whereas species in less constrained groups may be more tolerant of ecological transformations.

南美洲和中美洲被称为新热带地区，是地球上淡水鱼多样性最高的地区，超过7000种。然而，我们对产生如此令人难以置信的多样性的进化过程知之甚少。我和我的学生们研究了一种常见的新热带淡水鱼——慈鲷科的进化，并以此为模型来理解影响新热带淡水鱼进化的各种力量。慈鲷已经适应了生活在南美洲和中美洲的几乎每一种环境，形成了各种各样的形态和生态习性。我们假设慈鲷的多样性和生态多样性是由于早期扩展到新的、可用的生态资源（如食物和栖息地），产生了独特的、生态专门化的属。相比之下，在大多数这些属中，物种往往彼此相似，共享它们的形态（如体型和形状）和生态偏好（包括栖息地和饮食）。属内物种之间缺乏多样性可能源于生态机会的反面，即适应性约束。一旦一个谱系成为生态专家，它可能无法在与它所擅长的环境差异太大的环境中生存。这迫使专家的进化路径保持在所谓的“适应高峰”附近，在这个高峰周围，所有的生态、形态和生理条件都有利于它的生存。如果进化路径离峰值太远，物种就无法生存。在这个项目中，我们想要了解生态机会和适应性约束如何产生不同的进化结果。我们将通过研究美洲慈鲷的主要进化系（属）来实现这一点，并通过比较该组内的两个属：Crenicichla属的“pike慈鲷”和Apistogramma属的“dwarf慈鲷”。长形慈鲷的形态和生态位明显不同，而矮形慈鲷的生态和形态相似。虽然这两个属的物种数量相当，但鲷鱼可能是通过生态机会而多样化的，而矮鲷鱼可能是在严格的适应约束下进化的。这为研究这两种力量如何通过不同的机制产生多样性提供了一个自然的系统。我们将使用数百个DNA序列和化石记录来重建进化关系（家谱）以及美洲慈鲷，派克慈鲷和矮慈鲷的起源时间。然后，我们将使用过时的家谱作为路线图，了解这些鱼类在进化史上的不同特征是如何以及何时出现的。我们将追踪不同群体慈鲷的形态（摄食机制、游泳属性）和生态进化变化的速度和形式。通过比较不同群体的慈鲷，我们将了解生态机会和适应性约束如何促进美洲最多样化的鱼类之一的多样化。了解进化力量是如何塑造生物多样性的，对于从事保护工作或试图了解气候变化或其他环境变化的长期影响的生物学家来说也很重要。物种对环境变化的反应取决于它们对不同生态条件的适应能力。由此可见，属于具有严重适应约束的群体的物种可能无法忍受其环境的变化，而在较少约束的群体中的物种可能更能容忍生态转变。