The Genetic and Physiological Basis of Life Cycle Convergence

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9509802 One of the outstanding problems in ecological and evolutionary physiology is understanding the mechanisms by which major new features evolve. In particular, when we see the same adaptation in two or more unrelated species, we may ask the fundamental question "Do those species utilize the same physiological and genetic mechanisms to solve their adaptive problem, or do they use different mechanistic solutions to achieve the same adaptive solution?". An answer to this question is needed if we are to understand how organisms adapt to changing environments. To address this question, this research will use a model group of salamander species from Mexico and the US that have altered their physiological pathway to metamorphosis: some species go through a normal metamorphosis, while others forego metamorphosis and complete their lives as sexually mature, aquatic larval animals. Several strategies, ranging from molecular analyses of the genes responsible for metamorphosis, to administering hormones that regulate metamorphic completion, will be used to determine the mechanism used to achieve this ecologically important life-history shift in six different species of salamander. If the mechanism is the same in all species, this will indicate that there is essentially only one physiological and genetic mechanism by which this life-history shift can evolve, and all species have independently evolved the same solution. Alternatively, if different mechanisms are involved, there will be compelling evidence that truly independent solutions to the same adaptive problem can and do occur during evolution of closely related species. The research will introduce a novel approach for studying key adaptations, where both phylogenetic and molecular perspectives are simultaneously treated within a comparative, mechanistic framework. It will establish a case study linking ecological, physiological, and genetic levels of causation. The data will increase our understanding of the processes of evolution and the origin of biological diversity.