Immune defense adaptation of Strauchbufo raddei population in heavy metal polluted area: Insights from developmental and environmental perspectives

Abstract

The adjustment of immune defense mechanisms is a crucial aspect of biological adaptation to stressful environments. Amphibians, with their unique metamorphic process, experience distinct life stages and exhibit diverse immune defense components. While previous studies have focused on specific immune changes during particular life stages under stress, this research addresses a critical gap by exploring the adaptive immune defense strategies of Strauchbufo raddei in heavy metal-polluted environments. We conducted laboratory experiments, exposing offspring from both polluted and unpolluted areas to control and heavy metal treatments, while continuously monitoring changes in immune components during key metamorphic stages. Notably, we examined the role of the skin microbiome, a crucial but often overlooked barrier against pathogens. The results indicated that individuals from polluted areas exhibited some tolerance to heavy metal exposure, though overall immune function remained diminished. During metamorphosis, when immune defenses are most vulnerable, the skin microbiome rapidly enriched beneficial bacteria, preventing pathogenic colonization and playing a pivotal role in maintaining immune defense in contaminated environments. Moreover, our research highlights energy allocation strategies involving corticosterone and body fat content, enabling populations to maintain development despite immune compromise. The immune adaptations observed may be fixed through genetic assimilation, suggesting a rapid evolutionary response to environmental stress. However, this reduces phenotypic plasticity, making populations more vulnerable to future environmental changes. This study provides key insights into the survival strategies of amphibian populations in heavy metal-contaminated areas, laying the foundation for future research on molecular and evolutionary adaptations.