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Osmoregulation in the terrestrial Christmas Island red crab Gecarcoidea natalis (Brachyura: Gecarcinidae): modulation of branchial chloride uptake from the urine

H. H. Taylor^1,* and P. Greenaway²

¹ Department of Zoology, University of Canterbury, Private Bag 4800, Christchurch, New Zealand
² School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney 2052, Australia

View larger version (16K): [in a new window]   Fig. 1. Changes in the daily rate of release (triangles) and the chloride concentration (circles) of the final excretory fluid (P) of Gecarcoidea natalis before and after switching from fresh drinking water to 70% seawater ([Cl-]=360 mmol 1-1). Square, chloride concentration of the haemolymph. Values are means ± S.E.M.; where error bars are absent, they are smaller than the symbol. Numbers next to symbols are the numbers of crabs that produced P on that day and included in the mean [Cl-]. For all other means, N=9.

View larger version (20K): [in a new window]   Fig. 2. Chloride fluxes of crabs acclimated to fresh drinking water during bilateral perfusion of the branchial chambers with saline, partitioned into branchial uptake (red symbols), urinary output (green symbols) and ingestion of perfusate (oral). Values for urine flow and fluid ingestion may also be read as flow rates on the right-hand axis. Negative values indicate a loss from the crab. Values are means ± S.E.M. (N=8).

View larger version (15K): [in a new window]   Fig. 3. The relationship between the branchial rate of chloride uptake and the initial chloride concentration of the haemolymph for crabs acclimated to fresh drinking water and with the branchial chambers bilaterally perfused with saline. Triangles, initial (peak) rates (averaged over 0.5 h); circles, rates after 4.5 h of perfusion (averaged over 1 h). r2=0.68, P<0.01.

View larger version (20K): [in a new window]   Fig. 4. Chloride fluxes and fluid movements in crabs acclimated to saline drinking water (70% seawater), showing branchial uptake, urinary output and ingestion of perfusate (oral). Values are means ± S.E.M. (N=6). Other details as for Fig. 2.

View larger version (31K): [in a new window]   Fig. 5. The effects of dopamine and cyclic AMP on chloride fluxes and fluid movements in crabs acclimated to fresh drinking water showing branchial, urinary and oral fluxes. At time zero, 250µl 100g-1 total body mass of saline (A) or 1.0 mmol 1-1 dopamine (B) or 250µl 100g-1 total body mass of 6 mmol l-1 dibutyryl cyclic AMP (C) was injected pericardially. Values are means ± S.E.M. (N=5, 9 and 8, respectively). Other details as for Fig. 2.

View larger version (20K): [in a new window]   Fig. 6. The effects of acute NaCl-loading on the branchial uptake of chloride and urinary chloride flux for crabs acclimated to fresh drinking water. At time zero, 800 µl 100 g-1 total body mass of 5 mol l-1 NaCl was injected pericardially over 5 min, raising haemolymph [Cl-] by 78 mmol l-1. Values are means ± S.E.M. (N=4). Other details as for Fig. 2.

View larger version (20K): [in a new window]   Fig. 7. The effects of dopamine on branchial chloride fluxes in crabs acclimated to saline drinking water (70% seawater). Crabs were injected at time zero with 250 µl 100 g-1 total body mass of saline (open circles; N=8) or 1.0 mmol l-1 dopamine (filled circles; N=10). Values are means ± S.E.M.