Water Metabolism and Temperature Regulation of the Primitive Heteromyids, Liomys Salvani and Liomys Irroratus

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Abstract
Liomys salvani is able to maintain its body weight under laboratory conditions without free water when given a diet of wild bird seed, whereas Liomys irroratus is unable to maintain its weight under these same conditions. Both species can maintain weight when permitted to burrow even though free water is not available. The ad libitum water consumption of L. salvani was 5.5% body weight/day under laboratory conditions whereas it was 7.5% day for L. irroratus. The ad libitum consumption for L. irroratus was reduced 62% for individuals allowed to burrow. The average maximum urine concentration of L. salvani was 4,000 milliosmols whereas it was 3,580 for L. irroratus. The pulmocutaneous water loss was approximately the same for both species ranging between 0.90 to 1.03 mg H2O/cc O2 at a TA of 28°C, values comparable to those reported for other heteromyids at comparable ambient temperatures. The average biological half—life of water was the same for both species, ranging from 4 days when supplied with drinking water ad libitum to 6 days when deprived of water. Animals allowed to burrow exhibited a half—life of 6 days when deprived of water. Both L salvani and L. irroratus illustrate the characteristic heteromyid feature of poor tolerance to ambient temperatures above 34°C, though L. salvani is better able to resist lethal body temperatures when hyperthermic than can L. irroratus. Both species tolerated ambient temperature of 0°C for at least 1 hour. L. salvani and L. irroratus have basal metabolic rates 15 and 22%, respectively, below predicted. This reduction is probably characteristic of the heteromyids. The average basal metabolism was 1.12 cc O2/g—hr for L. irroratus and 1.07 cc O2/g—hr for L. salvani weighing 48.1 and 43.8 g respectively. Thermal neutrality extended from 31 to 34°C for both species. The insulation of both species as represented by the slope of the line relating metabolism to ambient temperature was .186 cc O2/g—hr—°C for L. Irroratus, values comparable to other heteromyids of similar body weight.

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