NDLI: Isometric spiracular scaling in scarab beetles—implications for diffusive and advective oxygen transport

Content Provider	Directory of Open Access Journals (DOAJ)
Author	Julian M. Wagner C. Jaco Klok Meghan E. Duell John J. Socha Guohua Cao Hao Gong Jon F. Harrison
Abstract	The scaling of respiratory structures has been hypothesized to be a major driving factor in the evolution of many aspects of animal physiology. Here, we provide the first assessment of the scaling of the spiracles in insects using 10 scarab beetle species differing 180× in mass, including some of the most massive extant insect species. Using X-ray microtomography, we measured the cross-sectional area and depth of all eight spiracles, enabling the calculation of their diffusive and advective capacities. Each of these metrics scaled with geometric isometry. Because diffusive capacities scale with lower slopes than metabolic rates, the largest beetles measured require 10-fold higher PO2 gradients across the spiracles to sustain metabolism by diffusion compared to the smallest species. Large beetles can exchange sufficient oxygen for resting metabolism by diffusion across the spiracles, but not during flight. In contrast, spiracular advective capacities scale similarly or more steeply than metabolic rates, so spiracular advective capacities should match or exceed respiratory demands in the largest beetles. These data illustrate a general principle of gas exchange: scaling of respiratory transport structures with geometric isometry diminishes the potential for diffusive gas exchange but enhances advective capacities; combining such structural scaling with muscle-driven ventilation allows larger animals to achieve high metabolic rates when active.
e-ISSN	2050084X
DOI	10.7554/eLife.82129
Journal	eLife
Volume Number	11
Language	English
Publisher	eLife Sciences Publications Ltd
Publisher Date	2022-01-01
Publisher Place	United Kingdom
Access Restriction	Open
Subject Keyword	Medicine Science Biology (general) Coleoptera Beetles Spiracle Morphology Scaling Body Size
Content Type	Text
Resource Type	Article

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