LEE, J.J.*; GLOMSKI, K.; TANNER, C.A.; BORST, D.W.; LOVETT, D.L.; The College of New Jersey, Ewing; The College of New Jersey, Ewing; The College of New Jersey, Ewing; Illinois State Univ., Normal; The College of New Jersey, Ewing: Hemolymph levels of Ca²⁺ may modulate methyl farnesoate levels in the green crab Carcinus maenas

When green crabs are transferred to dilute seawater (SW), hemolymph levels of methyl farnesoate (MF) increase transiently after 1-2 h, then decrease and subsequently increase to acclimation levels after 6-8 h. Because handling also causes MF levels to increase at 1-2 h, we used a flow-through system to change salinity without handling crabs. Using this protocol, MF levels increased 1-2 h after onset of hypo-ionic stress. Thus, MF increases at the same time that initial cell volume perturbations also would be anticipated. The role of specific ions in regulating MF levels was studied by exposing crabs to 27 ppt (iososmotic) artificial media in which ions were depleted to the levels in 5 ppt SW. MF levels were higher (P<0.05) in animals in Ca²⁺– or both Ca²⁺– and Mg²⁺-depleted media than those in complete 27 ppt medium. Likewise, crabs exposed to 5 ppt SW supplemented with both Ca²⁺ and Mg²⁺ to the levels found in 27 ppt SW, had lower (P<0.05) MF levels than crabs in unsupplemented 5 ppt SW. However, the addition of Ca²⁺ alone did not lower MF levels. Hemolymph levels of Ca²⁺ in crabs in 5 ppt SW and in 5 ppt SW supplemented with both Ca²⁺ and Mg²⁺were not different from each other, and were lower (P<0.05) than in crabs in 27 ppt SW. However, crabs in 5 ppt SW supplemented with only Ca²⁺ had hemolymph Ca²⁺ levels that were higher than those of crabs in 27 ppt SW. To examine the effects of Ca²⁺ on MF synthesis, mandibular organs (MOs) were incubated in Pantin�s saline with either low (5 mM) or normal (12.5 mM) Ca²⁺. MF levels were elevated in MOs incubated in low Ca²⁺. Therefore, Ca²⁺ may directly regulate MF levels. (Support: NSF grant IBN-0240903 to DWB and DLL; MDIBL and MBL Fellowships to DLL.)