Unexplored aspects of African mole-rat thermal biology: Daily energy expenditure and development of thermoregulation in Fukomys darlingi (Rodentia: Bathyergidae)

Abstract

In our study, we analyzed two poorly known aspects of thermal biology in subterranean rodents, the African mole-rats, that being daily energy expenditure and development of thermoregulation in juvenile mole-rat using the social Mashona mole-rat, Fukomys darlingi from southern Malawi. We performed laboratory measurements over 24 h to assess the daily energy expenditure (DEE) in adults as well as the development of the thermoregulatory abilities of juveniles at different ages. To assess the effect of ambient temperature (Ta), we exposed mole-rats to either 30 °C or 20 °C, which represents a thermoneutral as well as a thermally challenging temperature, respectively. The DEE at a Ta of 20 °C was lower than expected based on the calculation from the resting metabolic rate (RMR) at the same Ta, this suggested that heat derived from physical activity can substitute the thermoregulatory heat and thus decrease the cost on thermoregulation. To assess the development of thermoregulation in juveniles and the effect of the presence of family members on it, we measured core body temperature (Tb) and resting metabolic rate (RMR) in juveniles under several social contexts: while alone, with littermates, with littermates and mother and with littermates and both parents. Only juveniles older than one month could generate heat to keep Tb higher than Ta. Thermoregulation appeared to be fully developed in three-month-old juveniles. The presence of adult(s), but not littermates, helped to increase Tb and to decrease the RMR of juveniles. Although the results are mostly preliminary and some interpretations are limited due to low sample size in some social contexts, we may conclude that in this mole-rat species, development of thermoregulation is slow even compared to other altricial mammals.