Within-nest allometry of the bumblebee tracheal system

Howard, Jessica
The scaling of insect respiratory systems with body size has important implications for ecology and evolution of insects, ranging from allometry of aerobic performance to current and past environmental constraints on insect body size. Previous work examining scaling across beetle species and during ontogeny of grasshoppers suggests strong tracheal hypermetry, with larger insects investing relatively more volume in their tracheal systems. However, these approaches potentially confound body size differences with species or life stage differences in morphology or physiology. To circumvent these issues, we took advantage of large body size variation within bumblebee nests, with workers (sisters) varying 10-fold in body size from 50 to 500mg and queens exceeding 1g. We estimated tracheal volume, dimensions of pronotal and propodeal spiracles, and body size of individual bumblebees (Bombus impatiens) from lab-reared nests. We describe the allometry of tracheal morphology within and among bumblebee nests, and discuss implications for size-related performance, and for respiratory limitations on adult body size.
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