An Integrative Approach to the Ecological and Evolutionary Causes of Geographic Range Limits

拟议的研究将调查鱼类对盐度变化的生理反应。淡水生态系统的盐碱化已被确定为对生态系统产品和服务的重要全球威胁。然而，人们对盐度增加将如何影响淡水群落和生态系统知之甚少。拟议的研究将有助于对盐度如何改变一系列生理和行为特征以及这些变化如何反过来塑造地理分布和鱼类群落结构的机制理解。拟议的研究还包括以中学生为重点的教育推广部分。课堂上将使用活鱼，通过探究式的方法教授学生生物学概念。对试点项目的评估表明，学生对生物学概念的理解有所提高，考试成绩也有所提高。自然界中所有物种的地理分布都是有限的。事实上，生态学和生理学研究最基本的目标之一就是解释为什么某些生物体在某些环境中存在而在其他环境中不存在。地理范围的限制也提出了一个基本的进化问题；为什么种群不随着时间的推移而进化以占据更大范围的环境呢？对于大多数生物来说，这些简单的问题在很大程度上仍然没有答案，这限制了我们预测生物如何应对环境变化的能力。这一挑战持续存在，部分原因是地理范围限制的原因需要了解多种非生物和生物因素如何在环境中协同变化，以及不同特征的组合如何响应和适应这些挑战。在本文的研究中，研究了水蛭属中近缘的热带鱼的分布界限。当这些鱼一起出现时，它们沿着盐度梯度分离，但当它们单独出现时，它们跨越了广泛的盐度范围，这表明盐度耐受性和竞争相互作用共同塑造了分布界限和群落结构。研究的重点是渗透调节、行为攻击、激素、代谢范围和运动性能之间的相互作用。这些特征通常是单独研究的，然而，他们的联合研究揭示了关于共享机制如何以导致地理范围限制的方式影响多种特征的新假设。拟议的研究将使用实验室和实地实验来首先测试1)盐胁迫、种间竞争和捕食压力的能量成本升高如何使某些环境过于昂贵而无法持续生存；2)与渗透调节相关的激素变化如何损害竞争能力和食物获取。其次，本研究将结合实验室育种实验、基因组学方法和人工选择实验，探索基因流、加性遗传变异和负遗传相关在渗透调节和竞争能力的进化限制中的作用。总的来说，拟议的研究不仅提供了一个机会来测试地理范围限制的生态生理和进化原因，而且还提供了一个可以更广泛应用的综合框架。

The proposed research will investigate the physiological responses of fish species to altered salinity. Salinization of freshwater ecosystems has been identified as an important global threat to ecosystem goods and services. Yet very little is known about how increased salinity will impact freshwater communities and ecosystems. The proposed research will contribute a mechanistic understanding on how salinity alters suites of physiological and behavioral traits and how these changes in turn shape geographic distributions and fish community structure. The proposed research also includes an educational outreach component focused on middle school students. Live fish will be used in classrooms to teach students biological concepts through inquiry-based approaches. Assessments of a pilot program have shown improved student understanding of biological concepts and increased test scores.All species in nature show a limited geographical distribution. Indeed, one of the most fundamental goals of ecological and physiological research is to explain why some organisms occur in some environments and not others. Geographic range limits also pose a fundamental evolutionary question; why don't populations evolve over time to occupy a wider range of environments. Such simple questions remain largely unanswered for most organisms, limiting our ability to predict how organisms respond to environmental variation. The challenge persists in part because the causes of geographic range limits requires an understanding of how multiple abiotic and biotic factors covary in the environment, and how suites of different traits respond and adapt to these challenges. In the research proposed here, the distributional limits of closely related tropical fish species in the genus Poecilia are investigated. When these fish occur together they segregate along a salinity gradient, but when they occur alone they span a broad range of salinities, suggesting salinity tolerance and competitive interactions jointly shape distributional limits and community structure. The proposed research focuses on how osmoregulation, behavioral aggression, hormones, metabolic scope, and locomotor performance interact with each other. These traits are typically studied separately, however, their joint study reveals new hypotheses on how shared mechanisms can influence multiple traits in ways that lead to geographic range limits. The proposed research will use lab and field experiments to first test 1) how elevated energetic costs of salinity stress, interspecific competition, and predation pressure may make some environments too expensive to persist in, and 2) how hormonal changes associated with osmoregulation may compromise competitive ability and food acquisition. Second, the proposed research will explore the role of gene flow, additive genetic variation, and negative genetic correlations as evolutionary constraints on osmoregulation and competitive ability using a combination of lab breeding experiments, genomic approaches, and artificial selection experiments. Collectively, the proposed research not only offers an opportunity to test the eco-physiological and evolutionary causes of geographic range limits, but also provides an integrative framework that can be applied more broadly.