Microplastics disrupt adaptive predator-induced behavioural plasticity in Rana dalmatina tadpoles

The accumulation of microplastics (MP; plastic particles 1 m - 1 mm in diameter) in the environment is an increasing global concern. Although the physiological effects of MP on organisms, including humans, are increasingly documented, their impacts on behaviour are far less understood. Further, little is known about how MP affect adaptive phenotypic plasticity - the ability of a genotype to adaptively modify its phenotype in response to environmental cues. Anuran tadpoles are key models for studying phenotypic plasticity, with well-established evidence for predator-induced behavioural adjustments. Tadpoles typically reduce their activity and risk-taking when exposed to chemical cues released by predators, which has been proven to be adaptive. We investigated whether MP exposure from the fertilised egg stage alters the behaviour of agile frog (Rana dalmatina) tadpoles, and whether it interferes with their predator-induced behavioural plasticity. Tadpoles exposed to chemical cues from dragonfly larvae showed the expected antipredator response: these larvae showed significantly reduced movement activity and risk-taking. Although exposure to MP did not influence the behaviour of tadpoles that had not been exposed to predator cues, and also did not alter predator-induced changes in movement activity, it entirely abolished the predator-induced reduction in risk-taking. These results indicate that MP can compromise antipredator behaviour, increasing the vulnerability of individuals and natural populations to predation without causing visible developmental abnormalities. We recommend that future MP research targets behavioural traits with direct relevance to survival and reproduction, and examines how adaptive phenotypic plasticity is affected.