Dissertation Research: Evolution and Development of Left-Right Asymmetry in Echinoderms

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Dissertation Research: Evolution and Development of Left-Right Asymmetry in EchinodermsGregory Wray and Margaret PizerOne of the most active areas of research in evolutionary biology today concerns the origin of the unique morphological features seen in the different animal phyla. The members of the phylum Echinodermata (sea urchins, sea stars, sea cucumbers and their relatives) exhibit a number of features whose evolutionary origin has been the topic of extensive speculation among biologists for over a century. Perhaps the most striking of these characteristics involve echinoderm body symmetry. Echinoderm larvae are bilaterally symmetrical, while the adults show five-fold radial symmetry. The transition between these very different body symmetries occurs when adult structures develop on the left side of the larva, producing a left-right asymmetrical intermediate stage. Several scenarios have been proposed to explain the developmental transitions from bilateral symmetry to left-right asymmetry to pentaradial symmetry that occur during the echinoderm life cycle, but little testing of the predictions of these theories has been done using developmental data. This project involves a systematic study of the development of adult structures in echinoderms. The goals of this study are to investigate 1) the evolution of left-right asymmetry within echinoderms and 2) the developmental mechanism of left-right asymmetry in echinoderms and the evolutionary origin of this mechanism. To achieve these goals a variety of embryological techniques will be used, and results will be compared between different groups of echinoderms and between echinoderms and their relatives. A detailed study of the evolution and development of left-right asymmetry will result in a better understanding of the origin and evolution of echinoderm morphology. In addition, this study will provide insights into the evolution and development of left-right asymmetry in other phyla of animals and the evolution of metamorphosis in other marine invertebrates.