Evidence for chronotypes and associations with fitness-related traits in a wild insect

Consistent among-individual differences in the timing of daily activities are referred to as chronotype. While chronotype has been well studied in humans and some laboratory animals, field-based research remains scarce, particularly in insects. We studied an individually tagged population of crickets (Gryllus campestris) in a meadow in northern Spain. Using a network of 140 video cameras, we quantified the daily onset and cessation of activity, predator attacks, mating events and daily mortality in adults. We found small but consistent among-individual variation in both activity onset and cessation. Early onset of activity was associated with higher probability of mating, lower probability of being attacked and reduced mortality. Ceasing activity early had less pronounced fitness associations but was associated with higher mortality risk. This suggests that the timing of daily activity patterns is under selection and may reflect variation in individual quality. Greater within-individual variability in chronotype, which has been hypothesized to reflect adaptive flexibility, was associated with higher mating frequency, an increased probability of being attacked, but a lower overall mortality risk. Our findings provide rare evidence of chronotype consistency in a wild insect and highlight the potential fitness consequences of temporal behavioural variation.