Energetic costs related to isolation during dispersal in mole-rats, a laboratory approach

Although natal dispersal in the animal kingdom is an important phenomenon, it is very difficult to study, especially in animals with cryptic lifestyles. We studied the social aspect of dispersal by experimentally separating non-breeding adult giant mole-rats (Fukomys mechowii) from their natal families. Before and after separation, we estimated physiological and behavioural parameters related to energetics. After six weeks of separation animals had 25 % higher resting metabolic rate (RMR) at thermoneutral 30 °C, 35 % higher daily energy expenditure (DEE) at 30 °C and 22 % higher DEE at the thermally challenging 20 °C. Body mass, digging metabolic rate (DMR), digging speed and resting body temperature were unchanged However, post-digging temperature increase was 25 % lower, digging cost 10 % lower, and the DMR/RMR ratio 19 % lower than before separation. The increase in RMR in separated animals may be caused by changes in metabolic pathways and/or body composition. The higher DEE in separated animals at both T_as was probably caused by an increase in locomotor activity accompanied by elevated RMR. The smaller change in body temperature during digging in separated animals indicates a lower probability of overheating during this energy consuming activity while a lower digging cost in separated animals indicates that lone animals dig their tunnels more effectively. Overall, experimental social isolation, though not a full replication of natural dispersal, provides a practical means to study aspects of dispersal in mammals with extremely elusive way of life.