The energetics of the common mole rat Cryptomys, a subterranean eusocial rodent from Zambia

Body temperature, oxygen consumption, respiratory and cardiac activity and body mass loss were measured in six females and four males of the subterranean Zambian mole rat Cryptomys sp. (karyotype 2 n = 68), at ambient temperatures between 10 and 35 degrees C. Mean body temperature ranged between 36.1 and 33.2 degrees C at ambient temperatures of 32.5-10 degrees C and was lower in females (32.7 degrees C) than in males (33.9 degrees C) at ambient temperatures of 10 degrees C but did not differ at thermoneutrality (32.5 degrees C). Except for body temperature, mean values of all other parameters were lowest at thermoneutrality. Mean basal oxygen consumption of 0.76 ml O2.g-1.h-1 was significantly lower than expected according to allometric equations and was different in the two sexes (females: 0.82 ml O2.g-1.h-1, males: 0.68 ml O2.g1.h-1) but was not correlated with body mass within the sexes. Basal respiratory rate of 74.min-1 (females: 66.min1, males: 87.min-1) and basal heart rate of 200.min-1 (females: 190.min-1, males: 216.min-1) were almost 30% lower than predicted, and the calculated thermal conductance of 0.144 ml O2.g-1.h1.degrees C-1 (females: 0.153 ml O2.g-1.h-1.degrees C-1, males: 0.131 ml O2.g-1.h-1.degrees C-1) was significantly higher than expected. The body mass loss in resting mole rats of 8.6-14.1%.day-1 was high and in percentages higher in females than in males. Oxygen consumption and body mass loss as well as respiratory and cardiac activity increased at higher and lower than thermoneutral temperatures. The regulatory increase in O2 demand below thermoneutrality was mainly saturated by increasing tidal volume but at ambient temperatures < or = 15 degrees C, the additional oxygen consumption was regulated by increasing frequency with slightly decreasing tidal volume. Likewise, the additional blood transport capacity was mainly effected by an increasing stroke volume while there was only a slight increase of heart frequency. In an additional field study, temperatures and humidity in different burrow systems have been determined and compared to environmental conditions above ground. Constant temperatures in the nest area 70 cm below ground between 26 and 28 degrees C facilitate low resting metabolic rates, and high relative humidity minimizes evaporative water loss but both cause thermoregulatory problems such as overheating while digging. In 13-16 cm deep foraging tunnels, temperature fluctuations were higher following the above ground fluctuations with a time lag.(ABSTRACT TRUNCATED AT 400 WORDS)