SHAFER, T.H.; RAFFERTY, M.C.; LEM, S.; MONTOYA, L.M.; DREHS, C.M: Expression of genes potentially important for osmoregulation in blue crab (Callinectes sapidus) embryos and larvae

Blue crab embryos are exposed to increasingly salinity as the ovigerous females carrying them migrate to the mouths of estuaries in southeastern NC. Upon hatching, the zoea are planktonic in the open ocean. After the molt to megalopae, these larvae settle in the mouths of estuaries, undergo metamorphosis to juvenile crabs and rapidly move down the salinity gradient to other parts of the estuaries. This life cycle suggests interesting changes in the ability of embryonic, larval and juvenile blue crabs to osmoregulate. Reverse transcriptase-polymerase chain reaction (RT-PCR) was employed to investigate the expression of a number of genes coding for proteins potentially necessary for osmoregulation. Three such genes, sodium/potassium ATPase (alpha subunit), V-type hydrogen ATPase, and arginine kinase, are expressed in all stages examined: all embryos, the earliest stage zoea (hatched out in the laboratory) and late megalopae (obtained from settlement collectors placed near the mouth of the Cape Fear River). This gene expression was unaffected by treating the embryos or larvae at salinities between 35 and 5 ppt for one or two days. The lowest salinity had a detrimental effect on survival for the late stage embryos and the zoea but not for the early embryos or the megalopae. In contrast to the three genes above, the gene for the sodium/potassium/2 chloride cotransporter was on at all salinities in the embryos and zoea but off (and not inducible by low salinity) in the megalopae. Experiments are in progress to determine if the cotransporter gene is again transcribed (either constitutively or after hyposaline induction) in “first crabs” or older juveniles.