Life in plastic, it's not fantastic: Sublethal effects of polyethylene microplastics ingestion throughout amphibian metamorphosis

Microplastics (MP) are an abundant, long-lasting, and widespread type of environmental pollution that is of increasing concern as it might pose a serious threat to ecosystems and species. However, these threats are still largely unknown for amphibians. Here, we used the African clawed frog (<em>Xenopus laevis</em>) as a model species to investigate whether polyethylene MP ingestion affects amphibian growth and development and leads to metabolic changes across two consecutive life stages (larvae and juveniles). Furthermore, we examined whether MP effects were more pronounced at higher rearing temperatures. Larval growth, development, and body condition were recorded, and standard metabolic rate (SMR) and levels of stress hormone (corticosterone, CORT) were measured. We determined variation in size, morphology, and hepatosomatic index in juveniles to identify any potential consequences of MP ingestion across metamorphosis. In both life stages, MP accumulation in the body was assessed. MP ingestion was found to result in sublethal effects on larval growth, development, and metabolism, to lead to allometric carry-over effects on juvenile morphology, and to accumulate in the specimens at both life stages. In larvae, SMR and developmental rate increased in response to MP ingestion; there additionally was a significant interaction of MP ingestion and temperature on development. CORT levels were higher in larvae that ingested MP, except at higher temperature. In juveniles, body was wider, and extremities were longer in animals exposed to MP during the larval stage; a high rearing temperature in combination with MP ingestion counteracted this effect. Our results provide first insights into the effects of MP on amphibians throughout metamorphosis and demonstrate that juvenile amphibians may act as a pathway for MP from freshwater to terrestrial environments. To allow for generalizations across amphibian species, future experiments need to consider the field prevalence and abundance of different MP in amphibians at various life stages.

微塑料（Microplastics, MP）是一类分布广泛、留存持久且含量丰富的环境污染物质，因其可能对生态系统与物种构成严重威胁，日益受到学界关注。然而，目前学界对微塑料给两栖类带来的此类威胁仍知之甚少。本研究以非洲爪蟾（Xenopus laevis）为模式物种，探究聚乙烯微塑料（polyethylene MP）摄入是否会影响两栖类的生长发育，并在幼体（蝌蚪）与幼蛙两个连续生活史阶段引发代谢变化。此外，本研究还探讨了在更高饲养温度下，微塑料的影响是否会更为显著。研究人员记录了幼体的生长、发育情况与身体状况，并测定了其标准代谢率（standard metabolic rate, SMR）与应激激素皮质酮（corticosterone, CORT）水平。为明确变态过程中微塑料摄入可能带来的后续影响，本研究还测定了幼蛙的体型、形态变异与肝体指数。同时，在两个生活史阶段中，均对个体体内的微塑料积累情况进行了检测。研究发现，微塑料摄入会对幼体的生长、发育与代谢产生亚致死效应，会引发幼蛙形态的异速生长遗留效应，且在两个生活史阶段的个体体内均检测到微塑料积累。在幼体阶段，微塑料摄入会提升其标准代谢率与发育速率；此外，微塑料摄入与饲养温度对幼体发育存在显著的交互作用。除了在高饲养温度组外，摄入微塑料的幼体其皮质酮水平显著更高。在幼蛙阶段，幼体阶段暴露于微塑料的个体躯体更宽、四肢更长；但高饲养温度与微塑料摄入的联合作用抵消了这一效应。本研究结果首次揭示了微塑料在变态全过程中对两栖类的影响，并证实幼蛙可能作为微塑料从淡水生态系统向陆地生态系统迁移的载体。未来若要使研究结果可推广至其他两栖类物种，需在实验中考虑不同生活史阶段两栖类体内野外环境中各类微塑料的流行率与丰度。