Osmoregulation and water balance in the springhare ( Pedetes capensis )

Abstract

Springhares are large rodents that live in arid and semi-arid regions of Africa. We deprived springhares of water for periods of up to 7 days to determine what physiological adaptations. If any, enable them to survive in and regions without drinking. During water deprivation, springhares lost up to 30% body weight and produced a mean maximum urine concentration of 2548 mosmol kg-1 with a maximum of 3076 mosmol kg-1 in an individual animal. Haematocrit and plasma sodium and potassium concentrations were well regulated throughout water deprivation at 47.5 +/- 3.8% and 132.6 +/- 7.4 mmol l-1 and 3.5 +/- 0.7 mmol l-1, respectively, while plasma osmolality increased slightly from 293 +/- 12.5 mosmol kg-1 to 324 +/- 7.3 mosmol kg-1. Springhares thus appeared to be good osmoregulators and were able to maintain plasma volume during 7 days of water deprivation. In addition to the production of a relatively concentrated urine, water loss was limited by the lowered solute load and faecal water loss achieved by a reduction in food consumption and by the production of very dry faeces. These abilities, together with a favourable burrow microclimate and nocturnal activity pattern, enable them to survive in arid regions.

Differential osmoregulatory capabilities of common spiny mice (Acomys cahirinus) from adjacent microhabitats

“…Generally, when water availability is limited, animals respond by decreasing the volume of urine excreted and by increasing its concentration (e.g. in springhares Pedetes capensis; Peinke & Brown, 1999; in the desert mouse opossum Thylamys pusilla; Diaz, Ojeda & Dacar, 2001). The current results suggest that A. cahirinus are able to survive on a diet with high osmolarity and maintain water balance.…”

“…The current results suggest that A. cahirinus are able to survive on a diet with high osmolarity and maintain water balance. The ability of both NFS and SFS mice to concentrate the urine well above 3000 mosmol kg −1 shows that they both are relatively adapted to xeric conditions (Peinke & Brown, 1999), though their urine concentration capacity is still lower than that of their desert counterparts, Acomys russatus (Weissenberg & Shkolnik, 1994). In general, as diet salinity increased, the urine osmolality of mice increased in both seasons.…”

“…Within mammals, rodents are particularly susceptible to a high evaporative water loss because of their small body size and large surface area to volume ratio. Hence, they have developed mechanisms of decreasing water loss through a combination of behavioural and physiological means (Schmidt-Nielsen, 1964;Peinke & Brown, 1999). For example, they may conserve water by discharging concentrated urine, whilst gaining as much metabolic water and pre-formed water from their diet (Peinke & Brown, 1999).…”

“…Hence, they have developed mechanisms of decreasing water loss through a combination of behavioural and physiological means (Schmidt-Nielsen, 1964;Peinke & Brown, 1999). For example, they may conserve water by discharging concentrated urine, whilst gaining as much metabolic water and pre-formed water from their diet (Peinke & Brown, 1999). MacMillen (1983) investigated the ecological significance of this mechanism on several rodent species and found that urine concentration was negatively correlated with mean annual rainfall.…”

Multilevel analysis of the foraging decisions of western chimpanzees (Pan troglodytes verus) and resource scarcity in a savanna environment at Fongoli, Senegal

“…Minimizing energy expenditure in this way may prevent heat stress and dehydration. There is no evidence to suggest that they possess physiological adaptations to water conservation that can be found in several arid-adapted mammals, such as highly concentrated urine (desert rodents: Pannabecker 2013) or dry feces (springhares: Peinke and Brown 1999). Although we do not know how seasonality influences water balance in chimpanzees, studies of other nonhuman primates indicates that water scarcity has been a selective pressure in primate evolution.…”