Polyvinyl chloride microplastics modulate behavioral and biochemical phenotypic heterogeneity in Tribolium castaneum

Microplastic (MP) pollution poses an emerging threat to biodiversity, yet most studies focus on mean effects, overlooking the role of intraspecific variability in determining population resilience. From this perspective, we investigated whether exposure to polyvinyl chloride microplastics (PVC-MPs) reorganizes phenotypic heterogeneity in Tribolium castaneum, a terrestrial model of both ecological and experimental relevance. To this end, adults were exposed for seven days to a diet contaminated with PVC-MPs and compared with individuals maintained under baseline (control) conditions. We assessed survival rate, particle accumulation, and distinct behavioral biomarkers (across different paradigms), as well as biochemical endpoints predictive of oxidative stress, bioenergetic, neurochemical, and enzymatic alterations. Statistical analyses prioritized dispersion and structural metrics, including Gini's Mean Difference (GMD), entropy, heterogeneity tests (Fligner-Killeen and Energy distance), and the Multivariate Dispersion Network (MDN). The main results revealed that survival was higher in exposed individuals (92.2 %) despite pronounced particle accumulation, suggesting phenotypic modulation. Locomotor variability decreased (-24.7 %; 99.9 % PP), while spatial exploration, feeding response, and righting time increased in dispersion (+42-68 %; >97 % PP). At the biochemical level, we observed increased GMD in 5-HT, ROS, and AChE, accompanied by reduced digestive proteases and higher entropy, as well as integrated signatures linking behavioral responses to distinct physiological mechanisms. The MDN revealed collapsed modularity (≈ 0) and negative assortativity (-0.45), reflecting unstable covariance. Integrated heterogeneity metrics (GMD, CV, Shannon entropy) linked behavioral dispersion to physiological variation in 5-HT, ROS, total proteins, DA, and AChE activity. Thus, our findings indicate that PVC-MPs acted not only as toxic stressors but also as agents of intraspecific diversity reorganization, simultaneously promoting instability and canalization across different phenotypic axes. This reinforces the importance of heterogeneity-centered analyses in understanding the links between MP exposure, vulnerability, and population resilience, and further recommends their incorporation into ecotoxicological risk assessments.