9507358 Wourms Viviparity, i.e. giving birth to living young, first evolved among the vertebrates in fishes. Fishes display an extraordinary diversity of specializations for viviparity. The transition from oviparity (egg-laying) to viviparity established a variety of new functional relationships, one of which involves maternal-embryonic nutrient transfer. Specialized tissues, such as the placenta, evolved for transfer. Live-bearing goodeid fishes will be used as a model system to study maternal-embryonic nutrient transfer across a structure known as the trophotaenial placenta, comprised of the epithelial lining of the ovary and external projections of the embryonic intestine, termed trophotaeniae. The cellular basis of maternal-embryonic transfer of nutrients across the trophotaenial placenta will be characterized using fluorescence and electron microscopy and immunocytochemistry to trace the uptake, transport, and fate of proteins. The differentiation of embryonic gut and trophotaenial cells will be analyzed using fluorescence and electron microscopy. An evolutionary model that trophotaeniae evolved from embryonic gut tissue by an acceleration of the rates of cell division and differentiation in the hindgut relative to other regions of the gut and the overall growth of the embryo will be tested. These studies will enhance the understanding of viviparity; provide a detailed functional analysis of placental development in fishes; and contribute to evolutionary biology by elucidating the evolution of a new organ through modification of embryonic development. ***
