Developmental allometry of pulmonary structure and function in the altricial Australian pelican Pelecanus conspicillatus

Abstract

Quantitative methods have been used to correlate maximal oxygen uptake with lung development in Australian pelicans. These birds produce the largest altricial neonates and become some of the largest birds capable of flight. During post-hatching growth to adults, body mass increases by two orders of magnitude (from 88 g to 8.8 kg). Oxygen consumption rates were measured at rest and during exposure to cold and during exercise. Then the lungs were quantitatively assessed using morphometric techniques. Allometric relationships between body mass (M) and gas exchange parameters (Y) were determined and evaluated by examining the exponents of the equation Y=aM(b). This intraspecific study was compared to interspecific studies of adult birds reported in the literature. Total lung volume scales similarly in juvenile pelicans (b=1.05) as in adult birds (b=1.02). However, surface area of the blood-gas barrier greatly increases (b=1.25), and its harmonic mean thickness does not significantly change (b=0.02), in comparison to exponents from adult birds (b=0.86 and 0.07, respectively). As a result, the diffusing capacity of the blood-gas tissue barrier increases much more during development (b=1.23) than it does in adult birds of different sizes (b=0.79). It increases in parallel to maximal oxygen consumption rate (b=1.28), suggesting that the gas exchange system is either limited by lung development or possibly symmorphic. The capacity of the oxygen delivery system is theoretically sufficient for powered flight well in advance of the bird's need to use it.