Relaxed predation hinders development of anti‐predator behaviors in an aposematic beetle

Predation is a key force constraining the time and space in which prey can forage. Theoretical models propose that warning coloration (aposematism) may help unprofitable prey to extend their foraging niche without suffering the costs of predation. In this study, we show that aposematism can alter the development of those behaviors that are associated with detection by predators. The aposematic rove beetle P aederus fuscipes C urtis ( C oleoptera: S taphylinidae) harbors a symbiotic bacterium, which produces a non‐proteinaceous compound named pederin. We showed that pederin is highly toxic orally to insect predators and that adult P . fuscipes are well protected against predators. Field analysis revealed that P aederus is the most abundant genus of the tribe P aederini compared to five other closely related genera and that adult P aederus beetles are much more likely to be discovered during the day in open areas. In addition, laboratory analysis of common anti‐predator behaviors in P . fuscipes and three closely related, but non‐toxic, rove beetles revealed that non‐toxic beetles tend to seek refuge immediately after stimulation. Conversely, adult P . fuscipes are not adapted to conceal themselves even when intensely threatened. Instead, they walk in open areas and climb plant stalks, two behaviors that expose them to predators. These results imply that the chemical defense of P . fuscipes may have relaxed selective pressures on the development and maintenance of anti‐predator behaviors. These findings explain the unique biological characteristics of P . fuscipes beetles and provide evidence that aposematic animals may gain benefit by extending their foraging activities across both time and space.