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Microplastics Disrupt Predator-Induced Plasticity in Daphnia across Behavioral, Morphological and Molecular Levels
Summary
Tiny water fleas called Daphnia normally sense chemical warning signals from predators and change their body shape or behavior to protect themselves—but new research shows microplastics interfere with this survival instinct, especially plastics containing additional chemical additives. This matters beyond the pond: it shows microplastics can mess with animals' basic ability to sense danger and adapt, raising concerns about how these tiny plastic particles—now found throughout the environment and even in human bodies—might interfere with biological signaling in ways we don't yet fully understand.
Abstract Microplastics (MP) are widespread in aquatic ecosystems and pose a threat to freshwater biodiversity. While numerous studies examine physiological effects on aquatic organisms, less is known about how MP alter chemically mediated interactions that regulate predator–prey dynamics. Predator-induced defenses in Daphnia depend on detecting kairomones and represent an important form of adaptive phenotypic plasticity. Whether MP interfere with these responses, and through which mechanisms, remains unclear. Here, we show that polystyrene MP impair predator-induced defenses across Daphnia species by disrupting predator-cue-mediated plasticity at the behavioral, morphological, and molecular levels. In D. longicephala , chronic exposure to PS fragments weakened Notonecta -induced morphological defenses, whereas additive-containing PS fragments nearly suppressed defense formation and reduced body size. Consistent with these phenotypic effects, proteomic analyses revealed alterations in pathways related to molting and chitin metabolism, linking MP exposure to impaired defense formation. In D. magna , PS particles attenuated fish kairomone-induced diel vertical migration, with stronger effects for larger particles, consistent with reduced effective availability or perception of predator cues. Natural limestone particles caused only minor effects, indicating particle-specific rather than general particle-driven responses. Our findings demonstrate that MP can disrupt adaptive predator–prey interactions with potential cascading consequences for freshwater food webs.