Swamps and Faunal Diversification: Interdemic Variation in the Respiratory Ecology of East African Fishes

沼泽和动物区系多样化：东非鱼类呼吸生态的流行变异

• 批准号: 0094393
• 负责人: Lauren Chapman
• 金额: --
• 依托单位: University of Florida
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2001
• 资助国家: 美国
• 起止时间: 2001-02-01 至 2005-01-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0094393&HistoricalAwards=false
• 关键词: Swamps; Faunal; Diversification; Interdemic; Variation

For fishes, the availability of dissolved oxygen in the water can limit habitat quality and dispersal pathways. Oxygen-scarce (hypoxic) waters play a similar role to the absence of water for some fish species, creating a barrier to movement or limiting selection of alternative habitats. Oxygen scarcity has led to the evolution of varied morphological and physiological adaptations in fishes (e.g., development of air-breathing organs, large gills). These adaptations have associated costs and benefits that should affect the ability of fishes to colonize, inhabit, or disperse through deoxygenated waters. Despite great interest in the evolution of physiological and morphological adaptations to deoxygenation, the role of oxygen-scarce waters as barriers or biological filters and their impact on fish diversification is not well understood. This research program considers the evolutionary role of oxygen-scarce wetlands in fish faunal diversification by addressing the question of whether or not hypoxia acts as a strong selective force contributing to variation among populations of East African fishes.Oxygen scarcity is widespread in tropical fresh waters, particularly in dense wetlands, floodplain pools, and flooded forests. In East Africa, extensive hypoxic wetlands dominated by papyrus harbor air-breathing fishes like the African lungfish. Some non-air-breathing (water-breathing) fishes also occur, and these tend to be species with extremely efficient oxygen uptake mechanisms (e.g., very large gill surface area) or species inhabiting the edge of the swamp where interaction with open waters elevates the oxygen content of the water. Despite low numbers of fish species within dense wetlands, these habitats may be very important in the maintenance of fish diversity. For air-breathing fishes, wetlands are not likely to limit dispersal. However, for water-breathing fishes that cannot tolerate low oxygen conditions in the water, large swampy divides may isolate populations and lead to diversification and speciation. Even for some water-breathing fishes that can survive in dense swamps, habitat use and dispersal may still be limited by dissolved oxygen availability and oxygen uptake efficiency in the species. This may result in differences between swamp and open-water populations (i.e., neighboring populations of the same species may diverge in morphology or genetic makeup when one population lives in dense swamp and other populations live in well-oxygenated streams and rivers). Earlier studies by L. Chapman and colleagues demonstrated that swamp populations of three water-breathing African fishes have larger gills than populations of the same species in nearby well-oxygenated waters. Further studies on one of the species revealed differences in respiratory behavior and physiological characters between fish from swamp and fish from nearby well-oxygenated streams and rivers. However, the evolutionary mechanisms controlling these patterns of interdemic (between-population) variation are unknown. This research program uses a combination of field studies in Uganda and laboratory studies at the University of Florida to examine the degree to which oxygen scarcity contributes to interdemic variation in the respiratory biology of water-breathing East African fishes, and whether their respiratory biology is limiting habitat use and performance. The program focuses on one species from each of three major lineages of water-breathing fishes that inhabit both hypoxic swamps and well-oxygenated lakes and/or rivers: Barbus neumayeri (a minnow), Pseudocrenilabrus multicolor victoriae (a cichlid) and Gnathonemus victoriae (an electric mormyrid fish). This research expands on earlier studies of these species by evaluating the relative contribution of genetic and environmental influences on respiratory characters as well as physiological and behavioral performance under oxygen stress. A major question is how much of the variation in respiratory traits (e.g., gill size, hemoglobin concentration) between swamp and open-water populations is the result of genetic differences, and how much of the variation is due to phenotypic plasticity (change in characters in response to the environment that does not involve genetic change)? The project also considers whether the variation is adaptive, whether change in gill morphology impacts non-functionally related characters (i.e., do large gills constrain adjacent muscles such as those involved in feeding?), and the potential for interactions between phenotypes (large- and small-gilled fish) in the field. The evaluation of these questions will provide insight into how environmental patchiness (the swamp-open water mosaic) fosters evolutionary diversification of African fishes, and enhance our understanding of adaptive phenotypic plasticity versus local adaptation.

对鱼类来说，水中溶解氧的可用性可以限制栖息地的质量和扩散途径。对某些鱼类来说，缺氧水域与缺水水域的作用类似，为它们的活动制造了障碍，或限制了它们对其他栖息地的选择。缺氧导致了鱼类各种形态和生理适应的进化（例如，空气呼吸器官的发育，大鳃）。这些适应具有相关的成本和收益，应该会影响鱼类在缺氧水域的定殖、栖息或分散能力。尽管人们对缺氧生理和形态适应的进化非常感兴趣，但缺氧水域作为屏障或生物过滤器的作用及其对鱼类多样化的影响尚未得到很好的了解。本研究计划考虑缺氧湿地在鱼类区系多样化中的进化作用，通过解决缺氧是否作为一种强大的选择力，促进了东非鱼类种群的变化。氧缺乏在热带淡水中普遍存在，特别是在茂密的湿地、洪泛区水池和淹水森林中。在东非，以纸莎草为主的大面积缺氧湿地栖息着非洲肺鱼等呼吸空气的鱼类。一些不呼吸空气（水呼吸）的鱼类也会出现，这些鱼类往往是具有极其有效的氧气吸收机制的物种（例如，非常大的鳃表面积）或栖息在沼泽边缘的物种，在那里与开放水域的相互作用提高了水中的氧含量。尽管密集湿地的鱼类数量很少，但这些栖息地对维持鱼类多样性可能非常重要。对呼吸空气的鱼类来说，湿地不太可能限制它们的扩散。然而，对于不能忍受水中低氧条件的水呼吸鱼类来说，大的沼泽分隔可能会使种群隔离，并导致多样化和物种形成。即使对一些可以在密集沼泽中生存的水呼吸鱼类来说，栖息地的利用和扩散仍然可能受到物种的溶解氧可用性和吸氧效率的限制。这可能导致沼泽种群和开放水域种群之间的差异（即，当一个种群生活在茂密的沼泽中，而另一个种群生活在氧气充足的溪流和河流中时，同一物种的邻近种群可能在形态或基因组成上出现分歧）。查普曼（L. Chapman）及其同事的早期研究表明，沼泽中三种水呼吸的非洲鱼类的鳃比附近氧气充足的水域中的同类鱼类的鳃大。对其中一种鱼类的进一步研究表明，沼泽鱼类和附近氧气充足的溪流和河流中的鱼类在呼吸行为和生理特征上存在差异。然而，控制这些种群间变异模式的进化机制尚不清楚。该研究项目结合了乌干达的实地研究和佛罗里达大学的实验室研究，以检验缺氧在多大程度上导致了东非水呼吸鱼类的呼吸生物学差异，以及它们的呼吸生物学是否限制了栖息地的利用和性能。该计划的重点是生活在缺氧沼泽和氧气充足的湖泊和/或河流中的水呼吸鱼类的三个主要谱系中的一个物种：Barbus neumayeri（一种小鱼），Pseudocrenilabrus multicololvictoria（一种丽鱼）和Gnathonemus victoria（一种电鳃鱼）。本研究通过评估遗传和环境影响对呼吸特性以及氧应激下生理和行为表现的相对贡献，扩展了对这些物种的早期研究。一个主要的问题是，沼泽种群和开放水域种群之间呼吸特征（如鳃大小、血红蛋白浓度）的差异有多少是遗传差异的结果，又有多少是由于表型可塑性（不涉及遗传变化的特征变化对环境的反应）造成的？该项目还考虑了这种变化是否具有适应性，鳃形态的变化是否会影响非功能相关的特征（即，大鳃是否会约束邻近的肌肉，例如那些参与摄食的肌肉？），以及该领域表型（大鳃鱼和小鳃鱼）之间相互作用的潜力。对这些问题的评估将有助于深入了解环境斑块性（沼泽-开阔水域马赛克）如何促进非洲鱼类的进化多样化，并增强我们对适应性表型可塑性与局部适应性的理解。