Locomotion Reveals Contrasting Responses in Body Mass-Scaling of Metabolic Rates Between Winged and Wingless...

Metabolism fuels fundamental biological processes and commonly scales with body mass with an exponent, b, between 2/3 and 1. We, here, explore how differences in physical activity can reveal contrasting interspecific metabolic scaling between major groups of arthropods. The Metabolic-level Boundaries Hypothesis predicts that increased behavioural activity increases b. We test this hypothesis by comparing b during flight, non-flight locomotion, and rest in winged and wingless insects, and spiders. We find that interspecific b values increase with activity only with flight in winged insects which co-occurs with a substantial flight-related rise in metabolic level. Spiders show a shallower interspecific metabolic scaling relative to insects, potentially reflecting slower life-history strategies with increasing body size. Consequently, large resting or walking insects consume 6-15 times more oxygen than do spiders of corresponding size and activity level. These fundamental differences offer new insights into the evolutionary dynamics of arthropod energetics.