Phenotypic flexibility in amphibious fishes

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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.