Osmoregulation in juvenile and adultCyathura polita (Stimpson) subjected to salinity changes and lonizing gamma irradiation (isopoda, anthuridea)

Cyathura polita is a benthic, estuarine isopod found in restricted habitats, but normally tolerant of salinities between 0.5 and 32 ‰. Established populations ofC. polita are not found in the oceanic habitat or in fresh water. Their absence from these two habitats may be the result of the failure of some stage in the life cycle to osmoregulate. Measurements of freezing point depressions of the body fluids of juvenile and adultC. polita which had been subjected to salinities of 0.0 to 40 ‰ (NaCl) for 3 hours were used to show that both stages in the life cycle osmoregulate. At low salinities the juveniles and adults were equally able to osmoregulate. At the highest salinity, higher than in normal habitats ofC. polita, adults were better able to osmoregulate than juveniles. Part of the animals were subjected to 44,000 r of gamma irradiation from a Cs137 source and were then subjected to the various salinities. At low salinities the juveniles and adults of the irradiated group were equally able to regulate, and their ability was equal to that of the animals subjected to salinity changes alone. At the highest salinity, however, juveniles and adults that were irradiated had less ability to osmoregulate then the non-irradiated animals. Juveniles were more strongly affected by irradiation than adults. Irradiation, then, decreases the ability to osmoregulate only at the highest salinity.