Meeting Abstract

P3.108  Saturday, Jan. 5  Ca²⁺ levels in hemolymph regulate methyl farnesoate production by mandibular organs from the green crab Carcinus maenas LOVETT, D.L.**; NAGARAJU, G.P.C.; BORST, D.W.; The College of New Jersey, Ewing; University of Central Florida, Orlando lovett@tcnj.edu

Hemolymph levels of methyl farnesoate (MF), a hormone secreted by the mandibular organ (MO), increase in green crabs exposed to dilute seawater. We have demonstrated previously that this rise is due to the decreased Ca²⁺ and/or Mg²⁺ concentration rather than the decreased osmotic pressure of dilute sea water. Since Ca²⁺ levels in saltwater affect hemolymph levels of Ca²⁺, we tested the hypothesis that MF production by the MO is responsive to hemolymph levels of Ca²⁺. MO pairs were incubated in modified Pantin�s medium at high or low salinity (1000 or 600 mOsm/kg, which correspond to the hemolymph osmotic concentration of crabs acclimated to 33 ppt or 5 ppt seawater, respectively). One MO from each pair was incubated in medium with high (12 mM) Ca²⁺ and the contralateral MO was incubated in the same medium with low (3 mM) Ca²⁺. In both high and low salinity media, the MF content of MOs in high Ca²⁺ was approximately 40% lower than that of MOs in low Ca²⁺. Thus, in high salinity medium, MF content decreased from 9.5 (�1.3) ng MF/g crab in medium with 3 mM Ca²⁺ to 5.7 (�0.9) ng MF/g crab in medium with 12 mM Ca²⁺. Likewise, in low salinity medium, the MF content decreased from 15.6 (�2.3) ng MF/g crab in medium with 3 mM Ca²⁺ to 8.9 (�1.2) ng MF/g crab in medium with 12 mM Ca²⁺. These data suggest that decreased hemolymph Ca²⁺ levels of animals in dilute sea water are at least partly responsible for their increased hemolymph levels of MF. Because the MF content of MOs incubated in low salinity media was higher than the content of MOs in high salinity medium at both Ca²⁺ concentrations, an additional hemolymph factor (e.g. Mg²⁺) may also affect MF levels. (Support: NSF grant IBN-0611447 to DL and DB).