Abstract:
The doubly labeled water (DLW) technique and indirect calorimetry enable measurement
of an animal’s daily energy expenditure (DEE, kJ/day), resting metabolic rate (RMR,
kJ/d), sustained metabolic scope (SusMS), body fat content (BF, %) as well as water
turnover (WTO, ml/day), and water economy index (ml/kJ). Small mammals have been
the primary focus of many of the DLW studies to date. From large multi-species analyses
of the energetics and water flux of aboveground small mammals, well-defined trends
have been observed. These trends mainly refer to an adaptive advantage for lower
RMR, DEE, SusMS, WTO and WEI in more ariddwelling animals to increase water
and energy savings under low and unpredictable resource availability. The study of
the subterranean rodent family Bathyergidae (African mole-rats) has been of particular
interest with regards to field metabolic rate and metabolic studies. Although a great deal
of research has been conducted on the Bathyergidae, a complete overview and multispecies analysis of the energetics and water flux of this family is lacking. Consequently,
we assessed DEE, RMR, SusMS, BF, WTO and WEI across several different species
of bathyergids from various climatic regions, and compared these to the established
patterns of energetics and water flux for aboveground rodents. There was notable
variation across the Bathyergidae inhabiting areas with different aridities, often contrary
to the variations observed in above-ground species. These include increased DEE and
WEI in arid-dwelling bathyergid species. While the climate was not a clear factor when
predicting the SusMS of a bathyergid species, rather the degree of group living was a
strong driver of SusMS, with solitary species possessing the highest SusMS compared
to the socially living species. We conclude that the constraints of the underground
lifestyle and the consequent spectrum of social behaviors possessed by the family
Bathyergidae are most likely to be more crucial to their energetics and water flux than
their habitat; however other important unstudied factors may still be at play. More so,
this study provides evidence that often unreported parameters, measured through use
of the DLW technique (such as BF and WEI) can enable species to be identified that
might be at particular risk to climate change.
