Embryonic growth in viviparous matrotrophic fishes is facilitated by structural and functional adaptions for maternal-embryonic nutrient transfer. Although much is known about the mechanisms of such transfer in mammalian systems, some reptiles, and teleost fishes, very little information is available on sharks. Lombardi proposes to identify and examine the major cellular, developmental, and physiological mechanisms of maternal-embryonic nutrient transfer in two representative species of viviparous matrotrophic shark; Mustelus canis and Rhizoprionodon terraenovae. The ultrastructure and physiology of transplacental and paraplacental transfer will be examined. Objectives of this study are to: l) describe the ultrastructural morphology of both the maternal and embryonic adaptions for maternal-embryonic nutrient transfer; 2) establish a developmental series for both species; 3) determine nutrient transfer efficiencies for both species; 4) describe and quantify protein uptake by embryonic tissues in utero and in vitro; 5) analyze the composition of uterine secretions and maternal blood sera during gestation; 6)assess apendicular function in R. terraenovae; and 7) identify, characterize, and compare transplacental and paraplacental routes of protein transfer in both species. These studies are significant because they establish, for the first time, a morphological and physiological basis for maternal-embryonic nutrient transfer in viviparous matrotrophic sharks. Since many of the structures involved in maternal-embryonic nutrient transfer in higher vertebrates are also present in the sharks, the results of these studies will be integral to an understanding of the function and origin of the maternal-embryonic relationship in both the fishes and higher vertebrates.
