ARENDT, Jeff; University of California, Riverside: A Preliminary Framework for Integrating Evolutionary Ecology and Development

In order to link development with adaptive evolution we need to ask three questions: 1)What is the developmental basis of a given phenotypic trait? 2)How does variation in this trait depend upon the underlying developmental mechanism? and 3)What are the fitness consequences of different developmental mechanisms? The first question is the focus of developmental biology, which usually ignores intraspecific variation. A few micro-evolutionary studies have considered the developmental source of phenotypic variation, but fitness consequences are usually interpreted in terms of phenotype, not development. If the developmental mechanism is irrelevant for fitness, then development may have little to microevolution. I illustrate use of these three questions in a study of growth rate and swimming speed in anuran tadpoles. Rapid growth and fast burst swimming speed are important for increasing fitness in tadpoles. However, there appears to be a universal trade-off between these traits in aquatic vertebrates. This trade-off can in part be explained by characteristics of muscle development, but different development mechanisms act in different species. In the American toad, delayed differentiation of mature fibers results in fast-growing tadpoles having many, small, young fibers that make them slower swimmers. In the Western Spadefoot toad, production of extra-cellular matrix (connective tissue) means fast-growers have less muscle tissue per unit area of the tail, again making them slower swimmers. The trade-off between growth rate and swimming speed has its own fitness consequences, especially if predators are present. On going research is aimed at determining the effects of different developmental mechanisms for growth in ephemeral ponds and the range of plasticity in growth.