Adaptive modification of ingestive behavior in beach mice (Peromyscus polionotus).

The ability of an inland and beach race of the old-field mouse to use increasing concentrations of NaCl solutions was compared. Inland mice drank significantly more fluid at all concentrations than did beach mice. These differences became more pronounced as the salt concentration was increased. Food consumption was similar in both races while drinking water or a dilute salt solution, but beach mice ate significantly greater amounts when the concentration of salt was increased above 0.2 M. Weight losses on salt solutions were approximately equal in both races, although beach mice survived longer and tolerated the higher concentrations better. There was no difference in the ability of the races to concentrate urine or excrete Na⁺. When given a choice of distilled water or two salt solutions, beach mice consumed significantly more water (77%) than salt solutions (23%) whereas inland mice drank approximately equal amounts of water (54%) and salt solutions (46%). When deprived of anything to drink, beach mice almost stopped eating for the first two days while inland mice did not reduce their food consumption as quickly and died sooner. Thus, it appears that adaptive modifications of ingestive behavior are important for survival in habitats where salt accumlates and summer droughts may be a problem.