DISSERTATION RESEARCH: Life at the ocean surface: evolution and morphology of the Portuguese man of war

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The Portuguese man-of-war, Physalia physalis, drifts at the ocean surface. It is highly specialized for this environment using a gas-filled float as a sail to catch the wind and long tentacles as fishing line to capture small fishes and crustaceans. Physalia physalis is known to many beach goers for its painful sting, but despite being familiar and abundant, little is known about most basic features of this species. In this project, researchers will use new microscopy techniques to answer old questions about the anatomy, development, and evolutionary origins of this unique species. The products of this study will be made freely accessible to the public and other scientists via open access publishing. The award will also support lessons in a local elementary school on topics related to this project, including lessons on ocean zones, plankton, pleuston, and marine invertebrate body plans.Physalia physalis is the only siphonophore (Cnidaria: Hydrozoa) that is pleustonic (living at the interface between water and air). Siphonophores are colonial animals that are composed of zooids (bodies) that are each homologous to solitary animals. This project will describe fundamental features of P. physalis morphology and use phylogenetic comparative methods to reconstruct the evolutionary changes associated with a transition from a planktonic to pleustonic lifestyle. The primary product of this work will be a re-description of P. physalis, which also aims to address some of the following questions: how are zooids organized in P. physalis? How does P. physalis zooid morphology and colony organization differ from other siphonophore species, and what does this suggest about their evolution? Physalia physalis colonies have highly 3-dimensional branching structures. Optical Projection Tomography, as well as other immuno-fluorescent imaging methods, will be used to 3D-image fixed P. physalis tissue. These morphological descriptions will be compared with morphological descriptions available for planktonic siphonophores in order to investigate general patterns of character evolution within the siphonophore phylogeny.