Metabolic expenditure of submaximal locomotion in naked mole-rats (Heterocephalus glaber) and Damaraland mole-rats (Fukomys damarensis)

Despite extensive studies on the physiology of subterranean rodents, there is comparatively
little documenting the energetics specifically associated with their locomotory energetics.
The energetic cost associated with burrowing is great and, in part, explains why subterranean
species often maintain their burrows and tunnels across generations. Indeed, the digging
metabolic rate of five African mole-rat has been determined to be between three and five
times higher than that of their respective resting metabolic rate, yet the energetic cost of nondigging locomotion (i.e. walking) has not been recorded. Digging in most subterranean
species tends to lead to specialisation of the forelimbs and teeth which may significantly
affect the energetic cost associated with non-digging locomotion. Unlike many comparably
sized burrowing and tunnelling mammals, African mole-rats are unusual in that, superficially at least, they appear to have almost identical forelimbs and hind limbs. This study explored
the locomotory energetics associated with sustained submaximal locomotion (i.e., fast
walking; 10cm sec-1) in two African mole-rat species (F. damarensis and H. glaber), utilising
open-flow respirometry and a small animal treadmill. The mean locomotory energetic rate for
F. damarensis was a near 1-fold increase (91.4%) above resting metabolic rate and a 2-fold
increase (203.2%) increase for H. glaber. Net cost of transport (ml O2 kg-1 m-1) was higher
overall for H. glaber (2.9 ± 0.6) compared to F. damarensis (2.4 ± 0.5). A trade-off likely
exists between limb specialisation for digging and economic locomotion, and thus for most
obligately subterranean species, locomotion represents an energetic investment.