OSMOREGULATORY ROLE OF THE ANTENNARY GLAND IN TWO SPECIES OF ESTUARINE CRABS

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Abstract
1. Total osmotic pressure measurements of urine were determined on two species of crabs, Hemigrapsus nudus and H. oregonensis, over a salinity range, 6% to 175% sea water, three temperatures, 5°, 15° and 25° C., and at two seasons summer and winter. Blood data are included from Dehnel (1962) for comparison. 2. Urine and blood concentrations fall in dilute, and rise in concentrated media at rates directly related to the gradients between media and equilibrated body fluid concentrations, and are influenced by the seasonal adaptation of the animals and the experimental temperature. Major changes in body fluids occurred within 48 hours. 3. Hyper-osmotic regulation in summer-adapted animals resulted in isosmoticity of blood and urine, implicating extra-renal mechanisms. The production of hypo-osmotic urine in winter-adapted animals indicated the participation of the antennary glands. 4. In both species, summer and winter adaptation tended to favor stronger hyper-osmotic regulation at the respective seasonal temperatures than at temperatures foreign to the seasons. 5. Changes in experimental temperature revealed seasonal and interspecific differences in 48-hour blood and urine concentrations. Blood concentrations of H. oregonensis, when measured at a series of temperatures and salinities, showed a general trend, particularly for winter animals. As the concentration of the experimental media decreased (from 75% to 12%) blood concentrations increased significantly with decreasing temperature. Blood concentrations of summer animals showed no real differences, but when compared with winter crabs, at lower salinities, blood concentrations of summer crabs were significantly lower. The same general trend was shown for H. nudus. With respect to urine concentrations, summer-adapted H. oregonensis, in dilute media, showed significantly higher urine concentrations at higher temperatures. H. nudus showed no temperature effects in any salinities. Winter-adapted animals of both species showed significant decreases in urine concentration in low and intermediate, but not high, salinities, when the experimental temperature was increased. 6. Seasonal adaptation of osmoregulatory mechanisms in Hemigrapsus is shown to alter the balance of active processes so that for a given range of experimental conditions, urine is lower in winter animals than in summer, both in absolute concentration and relative to the blood.

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