ORIGINAL ABSTRACT

Glyphosate is one of the most widely used herbicides globally and is frequently detected in surface waters in multiple regions. Despite its toxicological relevance and potential ecological and human health implications (e.g., carcinogenity), its use was recently renewed in the European Union until 2033. A growing body of literature has showed that glyphosate can cause adverse effects in mollusks, but previous studies have focused primarily on survival, reproduction, genotoxicity, and certain cellular biomarkers, leaving its effects on molluscan behavior and embryonic development largely unknown. In the present study, we investigated the developmental, behavioral, and biochemical consequences of chronic glyphosate exposure on embryos of the widely used molluscan model, the great pond snail (Lymnaea stagnalis). Embryos were exposed from the single-cell stage to hatching to environmentally relevant concentrations of glyphosate (25, 100, and 500 μg L-1). All applied concentrations transiently delayed hatching without causing morphological abnormalities. Moreover, the highest concentration transiently increased heart rate, locomotion (gliding), and feeding, indicating elevated metabolic requirements. Biochemical analyses in hatched embryos demonstrated that all exposure concentrations significantly reduced vitellogenin content and lipid peroxidation, whereas a significant increase in catalase and lactate dehydrogenase (LDH) activity was observed only at the highest concentration, suggesting altered energy allocation and oxidative stress. Histochemical staining confirmed increased LDH activity, revealing tissue-specific metabolic activity, while no histological alterations were observed in hatched embryos. Collectively, our findings reveal previously unrecognized sublethal effects of glyphosate on molluscan embryos (e.g., altered heart rate, behavior, and cellular biomarkers), highlighting that this compound can disrupt growth, energy metabolism, and cellular homeostasis in Lymnaea embryos with potential consequences for post-hatching performance, resilience, and long-term fitness.