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Some Effects of Temperature and Concentration of the Medium on the Ionic Regulation of the Isopod Asellus Aquaticus (L.)
1 Department of Zoology, University of Cambridge and Department of Zoology, University of Edinburgh
1. Some effects of temperature and concentration of the medium on the sodium metabolism of the isopod Asellus aquaticus have been studied.
2. The steady-state haemolymph concentration rises with the temperature in the range 5-24° C. The change is, however, only a few mM./l. over this temperature range. The osmotic pressure (O.P.i) and sodium concentration of the haemolymph (Nai) also rise at temperatures below about 4-5° C.
3. The rate of sodium loss from the body is unaffected by temperature.
4. The rate of active uptake of sodium is increased as the temperature is raised.
5. The rate of active uptake of sodium is related to the haemolymph concentration, rising as the Nai falls.
6. The Nai is maintained at the normal level in media containing more than 90 µM./l. NaCl. Steady states can also be maintained at reduced haemolymph concentrations in media less concentrated than 90 µM./l.
7. It is suggested that the homeostatic mechanism regulating the Nai under the influence of temperature operates as follows. As the temperature falls there is a greater decrease in the rate of uptake than in the rate of loss and hence the Nai falls. A fall in the Nai, however, results in a rise in the rate of uptake. Therefore after a certain fall in Nai the loss is again balanced by uptake and a new but lower steady state is reached.
8. It is tentatively suggested that high temperatures may assist some brackish-water species in the invasion of more dilute media.
Submitted on March 15, 1960
