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Temperature and Water Relations in Two Species of Spiny Mice (Acomys)

Amiram Shkolnik , Arieh Borut
DOI: http://dx.doi.org/10.2307/1378340 245-255 First published online: 12 May 1969

Abstract

Temperature regulation and water economy were studied in two species of spiny mice, Acomys russatus and Acomys cahirinus. Both species share the same desert habitat in Israel, but A. russatus is active during the day and A. cahirinus is nocturnal. It was shown that A. russatus was better able to maintain its normal body temperature (TB) when exposed to high ambient temperatures (TA) and survived temperatures as high as 42.5°C. On the other hand, TA 40°C was lethal to A. cahirinus. Mean minimal metabolism of A. russatus was 34.5 per cent lower than the value predicted from body weight, and that of A. cahirinus was 13.5 per cent lower. A. russatus had no thermoneutral zone, oxygen consumption being minimal at TA 30°C. A. cahirinus had a narrow thermoneutral zone between 27 and 32.5°C TA. High ratios of evaporative water loss per milliliter of oxygen consumed were measured in both species; at 30°C it was 2.3 mg H2O/ml O2 in A. russatus and 1.9 mg H2O/ml O2 in A. cahirinus. When restrained at 30°C, 60 to 70 per cent of evaporation was from the skin. Maximum urine urea concentration in both species was 4700 to 4800 mM, among the highest recorded for mammals. Maximum chloride concentration was higher in the urine of A. russatus and amounted to 1500 mN, almost twice that of A. cahirinus. Accordingly, the capacity to utilize salt solutions for drinking was higher in A. russatus, which could drink sea water or NaCl solution as concentrated as 0.9 N. At 30°C, both species, when deprived of drinking water, failed to survive on a diet of barley. A. russatus could be considered physiologically better adapted for a diurnal existence than A. cahirinus, both in its ability to cope with high ambient temperatures and in its capacity to derive water from salty, succulent plants.

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