Scaling of gas exchange cycle frequency in insects

Previously, it has been suggested that insect gas exchange cycle frequency (f(C)) is mass independent, making insects different from most other animals where periods typically scale as mass(-0.25). However, the claim for insects is based on studies of only a few closely related taxa encompassing a relatively small size range. Moreover, it is not known whether the type of gas exchange pattern (discontinuous versus cyclic) influences the f(C)-mass scaling relationship. Here, we analyse a large database to examine interspecific f(C)-mass scaling. In addition, we investigate the effect of mode of gas exchange on the f(C)-scaling relationship using both conventional and phylogenetically independent approaches. Cycle frequency is scaled as mass(-0.280) (when accounting for phylogenetic non-independence and gas exchange pattern), which did not differ significantly from mass(-0.25). The slope of the f(C)-mass relationship was shallower with a significantly lower intercept for the species showing discontinuous gas exchange than for those showing the cyclic pattern, probably due to lower metabolic rates in the former. Insects therefore appear no different from other animals insofar as the scaling of gas exchange f(C) is concerned, although gas exchange f(C) may scale in distinct ways for different patterns.