Thyroid function and the development of endothermy in a marsupial, the Tasmanian bettong, Bettongia gaimardi (Demarest 1822)

The Tasmanian bettong (Bettongia gaimardi) is a small rat-kangaroo (marsupial) found only in Tasmania, Australia. The duration of pouch life is 15 weeks. Adults and older young display non-shivering thermogenesis and this paper examines the role of thyroxine in the development of endothermy in pouch young. Free thyroxine (T4) concentrations varied throughout pouch life. The mean (+/-SE) concentration was 6.2+/-1.9 pmol L-1 in week 7, increased and peaked at 19.2+/-4.3 pmol L-1 in week 12, and declined to 5.6+/-0.4 pmol L-1 by week 20. This was similar to adult levels (3.2+/-3.8 pmol L-1). These concentrations showed significant differences. From pouch week 12 onwards, T4 injection raised oxygen consumption. Maximum levels Of VO2 after T4 injection occurred at weeks 14-15. Although adult levels were lower, the increase in adult oxygen consumption after T4 injection was about 50%. Peak free T4 levels and metabolic responses to nor-adrenalin occur at week 12 and we hypothesize that thyroid hormone may facilitate the development of adrenergic-receptors in this species. The data presented in the paper further attest to the likely important role of the thyroid gland in the development of endothermy in marsupial pouch young. (C) 2003 Elsevier Inc. All rights reserved.