Allometric relations of respiratory variables in Amniota: Effects of phylogeny, form, and function

• Published in: Comparative biochemistry and physiology. Part A, Molecular & integrative physiology Molecular & integrative physiology, 2021-02, Vol.252, p.110845-110845, Article 110845
• Main Authors: Souza, Ray Brasil Bueno de, Bonfim, Vanessa Maria Gomes, Rios, Vitor Passos, Klein, Wilfried
• Format: Article
• Language: English
• Subjects: Aves; Crocodylia; Lung structure; Mammalia; Respiratory system; Scaling; Squamata; Testudines
• ISSN: 1095-6433; 1531-4332
• DOI: 10.1016/j.cbpa.2020.110845

Biological variables are frequently described by analyzing scaling relationships of the variable against body mass (MB). Respiratory variables are no exception and allometric relations for oxygen consumption, pulmonary ventilation, tidal volume, breathing frequency, and lung volume have been described in the literature. While the allometric relations of respiratory variables given for mammals and birds are very consistent among different studies, scaling relationships for non-avian reptiles have only been scarcely described and show considerable variation between studies. Since no comprehensive study of allometric relations of respiratory variables has been carried out comparing the different groups of non-avian reptiles, we analyzed morphological and physiological variables of the respiratory system of crocodilians, chelonians, lizards, snakes, birds, and mammals, regarding the allometric relations of each variable from a phylogenetic perspective as well as related to lung morphology. Our results indicated that few respiratory variables possess significant phylogenetic signals and that tidal volume, breathing frequency (except mammals), and air convection requirement were independent of phylogeny. Contrary to the literature, lung volume of amniotes scaled isometrically to MB, with the exception of lizards (MB0.78). Air convection requirement scaled isometrically in mammals and birds, but was more variable among non-avian reptiles, from a taxonomic perspective and in regard to different lung structures. In conclusion, respiratory variables among non-avian reptiles scaled more variably than previously expected, both according to phylogeny and to lung type, warranting future studies to explore structure-function relations of the reptilian respiratory system, especially regarding snakes and crocodilians, since these groups had very few data available for analysis. [Display omitted] •Allometric relations of respiratory variables have been analyzed from phylogenetic and functional viewpoints for amniotes.•Function related variables and air convection requirement were independent of phylogeny.•Lung volume of reptiles, excluding lizards (MB0.78), scaled isometrically with MB, just as seen in birds and mammals.•Air convection requirement scaled isometrically in mammals and birds, but was more variable among reptiles.•Crocodilians and snakes were very poorly represented in the literature, indicating need for future studies.