Evolution of Novel Ontogenies

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Raff9982644The goal of this project is to understand the mechanisms by which development evolves, and how developmental processes themselves influence or constrain the direction of evolution. Two species of sea urchins that are closely related but have highly different modes of early development will be used. Heliocidaris tuberculata develops in the ancestral indirect mode via a feeding larva, whereas Heloicidaris erythrogramma develops directly from embryo to juvenile adult. The project will identify genes that underlie developmental differences between the two species, define their expression patterns, and test their roles in producing an evolutionarily changed mode of development. The key to understanding the prospective role of gene expression changes in the evolution of early development comes from the recent creation of cross-species hybrids between the two species. Despite the different modes of development of the parent species, eggs of H. erythrogramma fertilized by H. tuberculata sperm develop via novel pathway in which a number of the primitive pluteus features are restored by the action of dominant factors derived from the paternal genome. Hybrids will be used to study how new larval features are generated, anad to isolate genes that regulate development of larval features. The specific aims are to (1) Determine the direction of cell lineage tracer dyes. Transformations of expression territories will be investigated using tissue-specific gene markers, and defined within the context of transformed cell lineages. (2) The expression patterns of genes isolated as candidates for the regulators of larval features modified or lost in evolution will be determined. (3) The function of genes implicated in appearance of larval features will be tested by over/ectopic expression experiments in the H. erythrogramma embryo. (4) Dominant inhibition of gene expression will also be used to study the roles of candidate genes. Specific phenotypes can be predicted, and thus the results of these experiments interpreted. The results of this project will provide an insight into the genic mechanisms that underlie evolutionary modifications of developmental processes, and into the role of constraints in the evolution of developmental process.