Water relationships in Natrix sipedon.
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Water relationships in two subspecies of the common water snake, N.s. confluens and N.s. clarki were investigated. Those snakes were collected along a transect from the City of Galveston, along the west shore of Galveston Bay and up the San Jacinto River. Since previous experiments had indicated differences in the mechanisms by which these two snakes maintained water balance, a further series of tests was conducted in an attempt to identify these differences. Permeability of the skin of these two races was tested with an osmometer. No water transfer through this organ could be demonstrated in either subspecies. It is concluded that the skin performs no role in water transfer. Differences in kidney structure were sought in a cursory histological investigation. No differences were observed. However, it is suggested that refinement of technique and more detailed study might show such a conclusion to be premature. A series of salinity discrimination and preference experiments showed that individuals of both subspecies preferred fresh water to sea water when they had only the alternative of being partially immersed in one or the other. It is concluded that clarki can maintain water balance through the utilization of preformed water from the body of its prey plus water derived from oxidative metabolism. Moreover, clarki will not drink water of 30 ppt salinity, whereas confluens will drink it and susequently succumb to its effects. Because of this behavior trait of confluens, a fresh water race, cannot occupy the salt marsh habitat where clarki regularly occurs.