Effect of water restriction on energy and water balance and osmoregulation of the fruit bat Rousettus aegyptiacus

Abstract

The energy budget, water balance and osmoregulation of the fruit bat, Rousettus aegyptiacus, were studied during normal hydration and during water restriction (oven-dried apple diet). The water input and output were balanced during both normal hydration and water restriction. The kidney of the fruit bat is well adapted to handle the water load from its fruit diet by excreting large volumes (14% of the body mass per day) of dilute urine (113 +/- 25 mosmol.kg H2O-1) as well as reducing urine volume (-95%) and increasing urine osmotic concentration (555 +/- 280 mosmol.kg H2O-1) during water restriction. The haematocrit, plasma haemoglobin and total protein concentrations did not increase during water restriction and heat exposure, suggesting the conservation of plasma volume. Gross energy intake was not affected by water restriction. However, digested energy intake and digestibility were significantly reduced. The effective regulation of energy and water budgets during water restriction suggests that the fruit bat can cope with seasonal climatic changes and with variable fruit supply during various seasons.

Absorption of sugars in the Egyptian fruit bat (Rousettus aegyptiacus): a paradox explained

“…NaCl was included in the solution to balance osmolality to approximately 300·mOsm. Inclusion of Na + also provides an essential ion for Na + -coupled D-glucose absorption (Brody, 1999), although it is not strictly necessary in this kind of whole-animal study because fruit bats routinely consume low Na + fruits (Arad and Korine, 1993;Nelson et al, 2000;O'Brien et al, 1998;Shanahan et al, 2001;Wendeln et al, 2000) and still absorb nearly all of the sugar (Keegan, 1984;Korine et al, 2004). Additional Na + is secreted into the intestinal lumen together with bicarbonate and diffuses from blood (Brody, 1999).…”

Relationships between renal morphology and diet in 26 species of new world bats (suborder microchiroptera)

“…Studier and Wilson (1983) showed that frugivorous bats produced an average urine concentration of 563 mOsm compared to 1643 mOsm in non-frugivorous bats. Other studies on frugivorous bats showed mean osmolality values for fruit bats of 619 and 113 mOsm (Studier et al, 1983a;Arad and Korine, 1993). A study on insectivorous bats showed an average urine concentration of 3225 mOsm (Geluso, 1978).…”

“…Moreover, several studies examined the renal anatomy and physiology within a single species (McFarland and Wimsatt, 1969;Studier et al, 1983a;Busch, 1988;Arad and Korine, 1993), while others examined multiple species (Carpenter, 1969;Geluso, 1978;Happold and Happold, 1988). These authors attempted to determine an association between various anatomical indices and urine concentrating ability.…”

The Influence of Ambient Temperature and the Energy and Protein Content of Food on Nitrogenous Excretion in the Egyptian Fruit Bat (Rousettus aegyptiacus)

“…We did not measure urine volume in this study because we could not separate urine from spilled food. Therefore, we estimated urine volume from reported relationships between water intake and urine volume, which are independent of diet composition in Egyptian fruit bats (Arad and Korine 1993;Korine 1996). From these relationships, we calculated the urine volume and the total amount of nitrogen excreted as uric acid, ammonia, and urea per day.…”