Hemolymph levels of methyl farnesoate increase in response to osmotic stress in the green crab, Carcinus maenas

The salinity of estuarine environments can vary widely; exposing resident o rganisms to considerable osmotic stress. The green crab Carcinus maenas is well known for its ability to osmoregulate in response to such stress. Ther efore, we tested the relationship between osmoregulation and hemolymph leve ls of methyl farnesoate (MF), a compound previously shown to rise in respon se to various types of environmental stresses. When crabs were transferred from 100% seawater to dilute (hypo-osmotic) seawater, hemolymph osmolality dropped rapidly, reaching an acclimation level 48 h after transfer. Hemolym ph levels of MF also rose in these animals after a delay of 6 h, and reache d a maximum level at 48 h. MF levels remained elevated as long as the crabs were maintained in dilute seawater, and quickly returned to basal levels w hen the animals were returned to full strength seawater. In most (but not a ll) animals, MF levels were elevated when hemolymph osmolality fell below t he isosmotic point (approx. 800 mOsm/kg). These data suggest that MF may ha ve a role in osmoregulation by this species. In addition, the elevation of MF by hypo-osmotic seawater suggests an experimental strategy for manipulat ing MF levels in crustaceans. (C) 2001 Elsevier Science Inc. All rights res erved.