Microplastic uptake with food increases risk-taking of a wide-spread decomposer, the common pill bug Armadillidium vulgare

Exposure to microplastics (MPs) i.e., plastic fragments between 1 μm and 1 mm in diameter causing growing concern for wildlife and humanity. It is now evident that MPs can accumulate in soil, freshwater, seawater and the atmosphere; thus, living organisms are directly or indirectly exposed to these significant ecological stressors globally. Studies on the physiological effects of MPs in wildlife are emerging, yet, to date, only a handful of studies with a special focus on how MPs affect animal behaviour are available, and there is even less research on how different components of among- and within-individual behavioural variation are affected by MPs. The main goal of this study was to investigate how prolonged exposure (6 weeks) to 10 μm spherical polystyrene microplastics in food (24.85 particles/mg) influences individual variation in risk-taking behaviour in a widespread decomposer, the common pill bug Armadillidium vulgare. Our results indicate a strong MP effect on different levels of behavioural variation: (i) individual mean risk-taking increased, while (ii) a correlation between mean risk-taking and residual within-individual risk-taking variation emerged (risk-takers became less predictable) in the MP treated group. These findings underscore the intricate effects of MPs on individual behavioural variation, with potentially far-reaching ecological and evolutionary consequences given their pervasive presence in both terrestrial and aquatic ecosystems. The negative impacts of these changes are widespread; in our study, MP exposure may increase the susceptibility of A. vulgare to predation, potentially contributing to population decline.