Predation promotes survival of beetles with lower resting metabolic rates

The energetic definition of fitness predicts that natural selection will maximize the residual energy available for growth and reproduction suggesting that energy metabolism might be a target of selection. In this experimental study, we investigated whether female and male yellow mealworm beetles, Tenebrio molitor L. (Coleoptera: Tenebrionidae), differ in their hiding behaviour, individual response latency time, and duration of immobility to treatments mimicking an approaching predation threat. We experimentally tested whether consistently repeatable anti-predatory responses and resting metabolic rates (RMR) correlated with survival rates of individuals exposed to a nocturnal predator, the brown rat, Rattus norvegicus (Berkenhout) (Rodentia: Muridae). Resting metabolic rate was part of a syndrome involving anti-predator behaviour. Individuals with lower RMR concealed themselves against predators in substrate more successfully than individuals with higher RMR, and hiding was associated with longer periods of immobility. Ultimately, mortality was higher in the high-RMR beetles compared to the low-RMR beetles. Our results provide direct evidence of natural selection against mobility, i.e., for reduced RMR in T.molitor beetles.