Body size is not critical for critical PO2 in scarabaeid and tenebrionid beetles

Hilary M. Lease, Cornelis J. Klok, Alexander Kaiser, Jon Harrison

Research output: Contribution to journalArticlepeer-review

26 Scopus citations


Constraints on oxygen delivery potentially limit animal body size. Because diffusion rates are highly distance dependent, and because tracheal length increases with size, gas exchange was traditionally thought to be more difficult for larger insects. As yet the effect of body size on critical oxygen partial pressure (Pcrit) has not been measured for any clade of insect species for which there are interspecific data on tracheal scaling. We addressed this deficiency by measuring Pcrit over a 4150-fold mass range (ratio of largest to smallest species mean) of two families of Coleoptera (Tenebrionidae and Scarabaeidae). We exposed adult beetles to progressively lower oxygen levels and measured their ability to maintain CO2 release rates. Absolute metabolic rates increased hypometrically with beetle body mass (M) at both normoxic (M0.748) and hypoxic (M0.846) conditions. Pcrit, however, was independent of body size. Maximum overall conductances for oxygen from air to mitochondria (GO2,max) matched metabolic rates as insects became larger, likely enabling the similar Pcrit values observed in large and small beetles. These data suggest that current atmospheric oxygen levels do not limit body size of insects because of limitations on gas exchange. However, increasing relative investment in the tracheal system in larger insects may produce trade-offs or meet spatial limits that constrain insect size.

Original languageEnglish (US)
Pages (from-to)2524-2533
Number of pages10
JournalJournal of Experimental Biology
Issue number14
StatePublished - Jul 2012


  • Allometry
  • Coleoptera
  • Insect
  • Metabolism
  • Oxygen delivery
  • Respiration
  • Scaling
  • Trachea

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Physiology
  • Aquatic Science
  • Animal Science and Zoology
  • Molecular Biology
  • Insect Science


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