Phenotypic flexibility in amphibious fishes

在脊椎动物的进化过程中，由于空气和水的性质非常不同，从生活在水中到迁移到陆地上的转变极具挑战性。 化石记录没有保留可能促进这种转变的软组织反应。 通过研究今天生活的两栖鱼类，我们可以揭示我们的鱼类祖先可能出现的各种特征和条件，使它们能够在水中繁衍生息。 总体假设是，血液氧气运输（目标1），皮肤（目标2）和骨骼肌（目标3）的特点已经发展出专门的功能，不同于非两栖鱼类，以及，可逆的可塑性在增强功能中发挥作用的鱼离开水。 我们将使用自我繁殖的两栖红树林鱼Kryptolebias marmoratus作为模式物种，以及精心挑选的密切相关的两栖和非两栖姐妹对测试10种新的假设，在鱼适应水和/或空气。 对于目标1，我们将收集血液样本并分析血红蛋白-氧结合，对血红蛋白肽进行测序以识别不同的亚型，并进行整体动物实验以确定呼吸性能。 对于目标2，我们将使用组织学方法来识别皮肤细胞类型和蛋白质转运蛋白定位，以及整个动物实验来确定呼吸和氮排泄的部位。 在目标3中，我们将使用组织学和生物化学方法来识别肌纤维类型和调节因子，并通过整体动物研究将呼吸和运动性能联系起来。 使用这种综合方法，我们将能够确定进化和机械因素，使两栖鱼类能够连接两个非常不同的世界，空气和水。

During the evolution of vertebrates, the transition from living in water to moving onto land was extremely challenging because of the very different properties of air and water. The fossil record has not retained the soft tissue responses that may have facilitated this transition. By studying amphibious fishes living today, we can uncover the variety of traits and conditions that may have arisen in our fish-like ancestors that allowed them to thrive out of water. The overall hypothesis is that blood oxygen transport (goal 1), and skin (goal 2) and skeletal muscle (goal 3) characteristics have evolved specialized features distinct from nonamphibious fishes and as well, reversible plasticity plays a role in enhancing function in fish out of water. We will use the self-fertilizing amphibious mangrove fish Kryptolebias marmoratus as a model species, as well as carefully selected closely-related amphibious and nonamphibious sister pairs to test ten novel hypotheses in fish acclimated to water and/or air. For goal 1, we will collect blood samples and analyze hemoglobin-oxygen binding, sequence hemoglobin peptides to identify different isoforms and conduct whole animal experiments to determine respiratory performance. For goal 2, we will use histological methods to identify skin cell types and protein transporter localization, as well as whole animal experiments to determine sites of respiration and nitrogen excretion. In goal 3, we will use histological and biochemical methods to identify muscle fiber type and regulatory factors, and whole animal studies to link respiratory and locomotory performance. Using this comprehensive approach, we will be able to identify evolutionary and mechanistic factors that have allowed amphibious fishes to bridge two very different worlds, air and water.