Evolution of development among gastropod molluscs

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Rudyard Kipling's Just So Stories have an enduring appeal because of our inherent fascination with bizarre features of animals and plants and our desire to know where they came from. How did flies get their wings? How did birds get their feathers? Interest in novel features of organisms is not only the stuff of quaint entertainments. Questions that ask how an organism acquired a feature that is obviously not present in otherwise similar organisms are of central importance to evolutionary biology. Novelties perplex biologists because, if natural selection works by modifying pre-existing structures, then how do seemingly new characteristics come into being in the first place? The need to explain morphological novelties has been a major impetus for bringing developmental biology back within the embrace of evolutionary biology. Biologists now recognize that small changes during the development of an organism, such as when a structure starts to form, can become magnified into large differences in the fully formed organism. I use gastropod mollusks as a model to study the development of novelties within this hugely diverse group of animals. I am investigating a hypothesis that may explain the highly contorted body plan of gastropods. Comparative studies of gastropod development suggest that the contorsion may have originated as an asymmetry in the development of the two sides of the body. I also seek to explain how predatory gastropods were able to evolve extraordinarily specialized feeding structures without compromising feeding activities of the larval stage. This issue has wide significance because most of the major groups of animals are invertebrates and their bodies are built within a life cycle that includes a larval stage. Needs of the larva may limit possibilities for adult evolution. Finally, I ask how swimming larvae of gastropods acquired the ability to feed and grow prior to metamorphosis. To study these questions, my students and I culture a wide variety of marine gastropods and we use various techniques for morphological analysis, such as scanning and transmission electron microscopy, computer-assisted 3D reconstruction of sectioned material, and immunolabeling to highlight structures and cells of interest.