A COMPARATIVE STUDY OF DAILY WATER-INTAKE AMONG CERTAIN TAXONOMIC AND GEOGRAPHIC GROUPS WITHIN THE GENUS PEROMYSCUS

¹ From the Carnegie Institution of Washington and the Scripps Institution of Oceanography of the University of California, La Jolla, California

1. Five subspecific groups of Peromyscus, representative of the two species, maniculatus and eremicus, have been tested in the laboratory to determine whether racial differences in water intake exist.

2. Significant differences were found between P. m. sonoriensis and P. e. eremicus, as well as between P. m. gambelii and P. e. fraterculus. No significant differences between P. m. rubidus and P. m. sonoriensis, nor between P. e. eremicus and P. e. fraterculus, were demonstrated.

3. It. is seen that, in these experiments, the only demonstrable differences in water intake are between the two species, P. maniculatus and P. eremicus, and not within either species. These specific differences in water intake are interestingly correlated with the geographic and ecological distributions of the two species.

4. Since the experimental data are based almost exclusively upon cage-bred stock, reared in a common environment, these differences appear to be hereditary.

5. Adequate statistical treatment, using McEwen's method, based upon "Student's" Probability Integral, indicates that these differences in water intake are real ones and not due to chance.