Abstract
In a recent article in PNAS, Clapham and Karr (1) related the maximum wing length (MWL) of different Odonatoptera and Orthoptera species to Phanerozoic atmospheric oxygen partial pressure (pO2) as predicted by the GEOCARBSULF model (2). They argued that the MWL data assigned to 10-Myr periods is well correlated with elevated Paleozoic pO2 levels, but that the correlation weakens and is ultimately decoupled during the Mesozoic and Cenozoic. To explain the correlation, they assumed that maximum insect size is constrained by a tracheal oxygen supply limit. To explain the decoupling, they referred to the notion that insect size increase results in reduction of flight maneuverability and increased aerial predation by birds (among others), i.e., a selective pressure against size increase also operates. This convenient mixed hypothesis deserves scrutiny.
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