EFFECT OF AIR-TEMPERATURE ON ENERGY AND WATER-BALANCE OF PSAMMOMYS-OBESUS

Fat sand rats (Psammomys obesus) are diurnal, desert-dwelling gerbillid rodents that can survive while consuming solely the saltbush Atriplex halimus, a chenopod high in electrolytes. To reduce electrolyte intake, fat sand rats scrape off the outer layers of leaves with their teeth before consuming them. We measured energy and water balances of fat sand rats offered A. halimus and maintained at 15, 21, and 34-degrees-C. They maintained body mass at 21-degrees-C, gained body mass at 34-degrees-C, but lost body mass at 15-degrees-C. Their dry matter intake was not significantly different among treatments, but dry matter digestibility and metabolizable energy of A. halimus was higher for fat sand rats at 34-degrees-C than at 15 and 21-degrees-C. Fat sand rats at 34-degrees-C produced the most concentrated urine and scraped off the most leaf material. As a result these fat sand rats secreted the lowest volume of urine, thus providing them with water required for evaporative cooling.