Plasticity of metamorphic traits in the Asiatic toad Bufo gargarizans: interactive effects of food quality and zinc pollution

Organisms with complex life cycles, like amphibians, are greatly affected by environmental factors and maternal effects, which in turn influence their morphological variation. The Asiatic toad Bufo gargarizans is found throughout East Asia and is not only valued for its economic medicinal properties in China but also considered a potential indicator species for assessing environmental pollution in inland rivers. However, the specific responses of this species to environmental toxicants, including trace metals, are not well comprehended at present. In this study, we experimentally examined the plasticity in larval period, body mass and size, and survival at metamorphosis in tadpoles of B. gargarizans under different combinations of food quality and zinc (Zn). We found that larval period, survival, SVL and mass at metamorphosis were sensitive to food quality, larval period increased significantly with increasing Zn concentration. The interaction between food quality and zinc primarily influenced the larval period. Tadpoles that were fed a high-energy diet, rich in protein and lipids, tended to have a shorter larval period as zinc concentration increased. Conversely, tadpoles fed a low-energy diet had a longer larval period with increasing zinc concentration. Thus, zinc plays a role in determining the extent to which food quality affects development of B. gargarizans. Additionally, larvae that consume a low-energy diet tend to have higher survival rates as zinc concentration increases, suggesting that moderate levels of zinc concentration (below 150 μg/L) are beneficial for normal physiological and biochemical processes in these organisms. The findings from this study provide valuable insights into the toxicological responses of this species to trace metals, contributing to a better understanding of their impact. Keywords: Bufo gargarizans, acute toxic effect, zinc, interaction effects, age and size at metamorphosis, phenotypic plasticity