Functional reorganization and systemic toxicity induced by microplastics and climate-relevant stressors in Tribolium castaneum: Are we simulating tomorrow's toxic reality?

Microplastic (MP) pollution and the intensification of global climate change raise concerns regarding potential interactions between these stressors and their ecotoxicological effects on terrestrial biota. In this study, we investigated the ecotoxicological effects of polyethylene MPs (PE-MPs) under different climate scenarios in Tribolium castaneum. Adults were exposed for 21 days to two environmentally relevant concentrations of PE-MPs (0.005 % and 0.1 %) under three contrasting temperature and CO₂ scenarios (27 °C/1000 ppm, 28.5 °C/1500 ppm, and 30 °C/2000 ppm). Behavioral, morphofunctional, and biochemical biomarkers were assessed using an integrative approach based on principal component analysis (PCA), factorial ANOVA, partial least squares-discriminant analysis (PLS-DA), and functional correlation networks. MPs induced significant structural alterations, including increased surface irregularity, a more compact body morphology, and loss of physical integrity, with marked effects in groups MP-II [27(1000)] and MP-II [30(2000)]. Anxiety-like behavior, hypoactivity, and locomotor disorganization were detected through PCA-derived integrated scores. At the same time, neuromotor dysfunction was evidenced by increased righting latency in group MP-II [30(2000)], and exploratory deficits were captured by the dispersal propensity index. Biochemically, groups MP-II [28.5(1500)] and [30(2000)] exhibited bioenergetic redistribution, reflected in altered integrated indices, alongside inhibition of digestive, antioxidant, redox, and neurochemical enzyme activities. Functional correlation networks revealed nonlinear reorganizations of biochemical architecture, with specific collapses and compensatory patterns. Network analysis identified MP-II [27(1000)] and [30(2000)] as the most functionally dissonant groups, with the highest MP accumulation in the latter likely responsible for the collapse of highly connected biomarkers. Thus, our study emphasizes that the impacts of MPs are not solely determined by exposure load or accumulation but also by the organism's systemic response capacity, expanding the understanding of their ecotoxicological effects under emerging climate scenarios.