TANNER, C.A.*; RICART, T.M.; BORST, D.W.; LOVETT, D.L.; College of New Jersey, Ewing; Mt. Desert Island Biol. Lab., Salisbury Cove, ME; Illinois State University: The effect of osmotic conditions on methyl farnesoate levels in the green crab, Carcinus maenas

We have shown previously that stress can increase methyl farnesoate (MF) levels in crustaceans. One type of stress that is particularly effective is exposure to dilute seawater. For example, transfer of green crabs (Carcinus maenas) from full-strength seawater (32 ppt) to dilute seawater (5 -15 ppt) causes a rapid and chronic rise in hemolymph levels of MF that are inversely related to decreases in salinity. In the present study we tested whether this increase in MF was due to osmotic or ionic stress by acclimating male crabs in mixtures of seawater and mannitol (added to increase the osmotic but not the ionic concentration of the solution). Hemolymph osmolality was low (548 � 20 mOsm/kg) (mean � SE) in dilute sea water (5 ppt; 170 mOsm/kg); hemolymph osmolality was normal (~ 850-950 mOsm/kg) in dilute seawater with mannitol (final osmolality 820 mOsm), isosomotic seawater (27 ppt, 830 mOsm/kg), and 20 ppt seawater with mannitol (final osmolality 985 mOsm/kg); hemolymph osmolality was elevated (1462 � 6 mOsm/kg) in concentrated seawater (50 ppt; 1490 mOsm/kg). In contrast, levels of MF in the hemolymph were elevated only in animals maintained in dilute seawater (four-fold increase in MF above basal levels) or in dilute seawater with mannitol (three-fold increase), and were normal in the other solutions. Thus, our results indicate that MF levels in the crab rise in response to hypo-ionic conditions, and not in response to hypo-osmotic or to hyper-osmotic conditions. Ion substitution studies currently are being conducted to determine which specific ion(s) may affect MF levels. (Supported by MDIBL NIA Fellowship to DLL, NIH grant HD37953 to DWB, and NSF REU Site at MDIBL DBI-0139190).