Daily temperature fluctuation exacerbates phenanthrene toxicity in Enchytraeus albidus: Links between membrane remodeling, lipid reserves, and reproduction

Climate change is intensifying daily temperature fluctuations (DTF), reshaping the thermal environment experienced by organisms. Most related studies have been conducted under constant high temperatures, and how intensified DTF affects pollutant toxicity and underlying mechanisms remains poorly understood. We exposed Enchytraeus albidus to phenanthrene (PHE; 0, 5, 10, 20, 40 and 80 mg kg −1 ) under four DTF regimes (mean 20 °C; amplitudes 0, 2, 5 and 7 °C) and measured internal PHE, the number of juveniles, and lipid composition. PHE and DTF showed a synergistic negative effect on the number of juveniles, with EC 50 decreasing from 46 to 23 mg kg −1 as DTF amplitude increased, while internal PHE did not differ significantly among DTF regimes. Membrane phospholipid unsaturation and storage lipid reserves were reduced as PHE concentration and DTF amplitude increased. Correlation analysis further showed that variation in the number of juveniles was significantly associated with changes in membrane phospholipid unsaturation and storage lipid reserves, and their response patterns were generally consistent across treatments. Overall, by linking variation in the number of juveniles with concurrent changes in membrane phospholipids and storage lipids, these results provide possible mechanistic insight into how intensified DTF modulates PHE toxicity and further emphasize the need to explicitly consider DTF in risk assessment under climate change.