Seymour Roger S, Runciman Sue, Baudinette Russell V
Environmental Biology, University of Adelaide, Adelaide, S.A. 5005, Australia.
Comp Biochem Physiol A Mol Integr Physiol. 2008 Jun;150(2):169-75. doi: 10.1016/j.cbpa.2006.03.018. Epub 2006 Apr 7.
The Australian Brush Turkey Alectura lathami is a member of the Megapodiidae, the mound-building birds that produce totally independent, "superprecocial" hatchlings. This study examined the post-hatching development of resting and maximal metabolic rates, and the morphometrically determined changes in pulmonary gas exchange anatomy, in chicks during 3.7 months of growth from hatchlings (122 g) to subadults (1.1 kg). Allometric equations of the form y=aM(b) related gas exchange variables (y) to body mass (M, g). Metabolic rates were measured with open-flow respirometry (mL O2 min(-1)) of chicks resting in the dark and running above the aerobic limit on a treadmill. Resting metabolic rate (RMR=0.02 M(0.99)) and maximal metabolic rate (MMR=0.05 M(1.07)) scaled with exponents significantly above those of interspecific allometries of adult birds. However MMR was below that expected for other species of adult birds in flapping flight, consistent with the Brush Turkey's ground-dwelling habits. Total lung volumes (mL) increased faster than isometrically (V(L)=0.0075 M(1.19)), as did the surface area (cm(2)) of the blood-gas barrier (S(t)=7.80 M(1.23)), but the data overlapped those of adult species. Harmonic mean thickness of the blood-gas barrier was independent of body size (mean tau(ht),=0.39 microm) and was about twice that expected for flying birds. Diffusing capacity (mL O2 min(-1) kPa(-1)) of the blood-gas tissue barrier increased faster than isometrically (Dto2=0.049 M(1.23)); in hatchling Brush Turkeys, it was about 30% expected for adult birds, but this difference disappeared when they became subadults. When compared to altricial Australian pelicans that hatch at similar body masses, superprecocial Brush Turkeys had higher MMR and higher Dto2 at the same body size. A parallel allometry between MMR and Dto2 in Brush Turkeys and pelicans is consistent with the concept of symmorphosis during development.
澳大利亚刷尾火鸡（Alectura lathami）是冢雉科的一员，冢雉科是一类筑巢的鸟类，其幼雏完全独立，属于“超早成雏”。本研究考察了从雏鸟（122克）成长至亚成鸟（1.1千克）的3.7个月期间，雏鸟静息代谢率和最大代谢率的孵化后发育情况，以及通过形态测量确定的肺气体交换解剖结构的变化。采用y = aM(b)形式的异速生长方程，将气体交换变量（y）与体重（M，克）相关联。代谢率通过开放式流动呼吸测定法（毫升O₂ 分钟⁻¹）进行测量，分别测量雏鸟在黑暗中静息时以及在跑步机上高于有氧极限奔跑时的代谢率。静息代谢率（RMR = 0.02M(0.99)）和最大代谢率（MMR = 0.05M(1.07)）的标度指数显著高于成年鸟类的种间异速生长指数。然而，最大代谢率低于其他成年鸟类在振翅飞行时的预期值，这与刷尾火鸡的地栖习性一致。总肺容量（毫升）的增长速度快于等比增长（V(L) = 0.0075M(1.19)），血气屏障的表面积（平方厘米）（S(t) = 7.80M(1.23)）也是如此，但这些数据与成年物种的数据重叠。血气屏障的谐波平均厚度与体型无关（平均τ(ht) = 0.39微米），约为飞鸟预期值的两倍。血气组织屏障的扩散容量（毫升O₂ 分钟⁻¹ 千帕⁻¹）的增长速度快于等比增长（Dto2 = 0.049M(1.23)）；在雏鸟阶段，刷尾火鸡的扩散容量约为成年鸟类预期值的30%，但当它们成为亚成鸟时，这种差异消失了。与孵化时体重相似的晚成雏澳大利亚鹈鹕相比，超早成雏的刷尾火鸡在相同体型下具有更高的最大代谢率和更高的扩散容量。刷尾火鸡和鹈鹕的最大代谢率与扩散容量之间的平行异速生长关系与发育过程中的对称生长概念一致。
