ENERGY-METABOLISM AND THERMOREGULATION IN THE GOLDEN LION TAMARIN (LEONTOPITHECUS-ROSALIA)

Energy metabolism and body temperature were examined in Leontopithecus rosalia, the golden lion tamarin. Total standard metabolic rate (SMR) , defined as the metabolic rate of resting, fasted animals within ther moneutrality and during the inactive (nighttime) phase, averaged 381.5 +/- 65.2 ml O-2 . h(-1) (mass-specific metabolic rate 0.520 +/- 0.089 ml O-2 . g(-1). h(-1)). This value ranges from 73 to 89% of the expec ted SMR for animals of this body size depending on the predictive equa tion used. Active-phase resting metabolic rate within thermoneutrality was significantly greater than SMR, averaging 509.0 +/- 44.6 ml O-2 . h(-1) (0.709 +/- 0.062 ml O-2 . g(-1). h(-1)). Thermal conductance du ring the inactive phase was 20.3 +/- 2.7 ml O-2 . h(-1).degrees C-1 (0 .029 +/- 0.003 ml O-2 . g(-1). h(-1).degrees C-1) or 70% of that durin g the active phase (28.5 +/- 3.2 ml O-2 . h(-1) .degrees C-1, 0.042 +/ - 0.004 ml O-2 . g(-1). h(-1).degrees C-1). These values are about 85% of the mammalian predicted value. Body temperature fluctuated substan tially between day (39.6 degrees C) and night (37.4 degrees C). Howeve r, none of these differences between circadian phases are unusual for primates (or, indeed, mammals) of similar body size. Although the meta bolic rate of Leontopithecus is lower than the predicted one, it is hi gher than those rates reported for small nocturnal primates with simil ar food habits. Leontopithecus' modest rates of energy turnover may re flect a combination of phylogenetic constraints, feeding ecology and/o r an energy-saving tactic that comprises part of a strategy to maximiz e reproductive effort. Although callitrichids are often cited as havin g rapid growth and high reproductive effort, the moderately low SMR of Leontopithecus is consistent with its intrinsic rate of natural incre ase, which is 90-94% of that expected for a mammal of its body size.