The response of life history defense of cladocerans under predation risk varies with the size and concentration of microplastics

Highlights: • Cladocerans live in aquatic environment where microplastics and predators coexist. • The effect of microplastics on plasticity is related to cladocerans species. • Microplastics have a size-based inhibitory effect on life history of cladocerans. • The inhibitory effect of 0.7 µm microplastics is more serious than that of 1 µm. • Medium-sized cladoceran is more sensitive to microplastics than small-sized one. Microplastics are an emerging and increasingly serious pollutant in freshwater environment, which have become a threat to freshwater organisms. However, whether microplastics interfere with the responses of organisms to their predators is still unclear. In this study, we investigated the effects of microplastics with tiny different particle size (diameter: 0.7 and 1 µm) on the anti-predation (Rhodeus ocellatus as the predator) defense responses of different body-sized cladocerans, Daphnia pulex and Moina macrocopa. Results showed that microplastics had a size-based inhibitory effect on the induced defense of both D. pulex and M. macrocopa. Specifically, 0.7 µm microplastics had stronger effects on reduced survival time, delayed maturation time, and decreased offspring numbers. In addition, the effects of microplastics also varied with different body-sized cladocerans, i.e. medium-sized cladoceran (D. pulex) were more sensitive than the small-sized one (M. macrocopa) regarding the maturation time. This study illustrated for the first time that the effect of microplastics on induced defense was related to cladoceran species and microplastics size, and further revealed the extensive negative effects of microplastics from the perspective of interspecific relationship.