Development of endothermy in a tasmanian marsupial, Bettongia gaimardi and its response to cold and noradrenaline

Abstract

Marsupials at birth are ectothermic and gradually attain the ability to change their metabolic heat production during pouch life. How this process occurs in the bettong has been measured on 13 pouch young from week 1 until 3 weeks after pouch vacation (week 18). Oxygen consumption was measured at 35 degrees C (pouch temperature) and at 22 degrees C. The results at 35 degrees C showed an increase in metabolic rate from week 1 until week 12 when there was a decrease to near adult levels after pouch vacation. At 22 degrees C young bettongs had a lower metabolic rate (compared with measurements made at 35 degrees C) until week 9 after which there was an increase above measurements made at 35 degrees C. Noradrenaline had little effect until week 10 after which the metabolic rate (although measured at 35 degrees C) paralleled the levels measured at 22 degrees C. The free thyroxine level was low in early pouch life, increased to a peak at week 12 then decreased. Thermal conductance increased until week 10 after which it decreased, reaching values similar to those of adult bettongs by week 20. The results indicate that non-shivering thermogenesis occurs in this macropodoid marsupial. This phenomenon may be a phylogenetic difference between macropodid and non-macropodid marsupials as also suggested by Nicol et al. (1997).

Scaling of left ventricle cardiomyocyte ultrastructure across development in the kangaroo Macropus fuliginosus

“…From a whole-organ perspective, the increasing volume-density of myofibrils is consistent with the observation that stroke volume is significantly depressed in neonate lambs at afterloads that are modest for adults (Downing et al, 1965). From a whole-animal perspective, the hyperallometry of myofibril volume-density and absolute volume, and the associated increase in relative cardiac contractile performance, would augment cardiac output during in-pouch development and in the lead up to pouch vacation, and thus almost certainly facilitate the kangaroo's transition from ectothermy to endothermy (Hulbert, 1988;Loudon et al, 1985;Rose et al, 1998) and independent locomotion (Dawson, 2012).…”

“…Perhaps the most important cardiovascular life history event for marsupials occurs when the emergent young vacates the maternal pouch. In kangaroos and other marsupials, the period leading up to permanent pouch exit is associated with the development of endothermy and an increase in metabolic rate (Hulbert, 1988;Rose et al, 1998). Around the same time, kangaroos make brief excursions from the pouch, which continues until the animal is capable of sustained and independent locomotion (Dawson, 2012).…”

Brown adipose tissue: physiological function and evolutionary significance

“…The NST-capacity values were determined as the difference between the maximum VO 2 after noradrenaline injection and the basal metabolic rate (BMR) (the resting metabolic rate (RMR) in some cases) further claimed the absence of BAT in 37 other marsupial and one monotreme (prototherian) species. In addition to these morphological findings, in vivo studies found equivocal responses of typical noradrenaline-stimulated metabolic rate (Nicol 1978;Smith and Dawson 1984;Loudon et al 1985;Dawson and Olson 1988;Ye et al 1996;Nicol et al 1997;Clements et al 1998;Rose et al 1998Rose et al , 1999Opazo et al 1999;Polymeropoulos et al 2012). At this historical stage, only one study has reported on molecular hints for BAT in marsupials by immunological detection of UCP1 using heterologous eutherian antibodies (Hope et al 1997).…”

Shivering, muscle tone, and uncoupling proteins in a developing marsupial, the Tasmanian bettong (Bettongia gaimardi)

“…Marsupials are born naked and ectothermic (Loudon et al, 1985;Gemmell et al, 1987;Rose, 1987;Hulbert, 1988;Rose et al, 1998). The ability to metabolically thermoregulate gradually develops while in the pouch (Loudon et al, 1985;Rose et al, 1998). Loudon et al (1985) reported a critical age, approximately 12 weeks of pouch life, at which pouch young Macropus rufogriseus were able to respond to an injection of NE by increasing their resting oxygen consumption rate, thereby suggested the maturity of endothermy.…”

“…Marsupials are born naked and ectothermic (Loudon et al, 1985;Gemmell et al, 1987;Rose, 1987;Hulbert, 1988;Rose et al, 1998). The ability to metabolically thermoregulate gradually develops while in the pouch (Loudon et al, 1985;Rose et al, 1998).…”