Microplastic exposure induces locomotory responses in wood frog (Rana sylvatica) tadpoles

The observed effect of microplastics on aquatic animal behaviour varies between species and studies. We examined wood frog (Rana sylvatica) tadpoles exposed to a mixture of microplastics at varying concentrations to test the hypothesis that chronic exposure to microplastics throughout development (from eggs to Gosner Stage 30-36) would alter behaviour. We used equal parts polystyrene, polypropylene, and polyethylene terephthalate fragments with additives at 1× (50,000 microplastic particles·L), 10× (500,000 microplastic particles·L), or no microplastics (negative control). Wood frog embryos were collected and exposed to the microplastic mixture for 49 days. Following the exposure, tadpoles were placed into arenas and video-recorded for 10 min. Automated tracking (Ethovision XT14) was then used to quantify various behaviours. Tadpoles exposed to 1× treatment had fewer bouts of moderate activity, and there were non-statistically significant trends toward negative effects of microplastics on swimming velocity and distance travelled compared to the control tadpoles. Additionally, tadpoles exposed to 10× treatment spent less time in a high activity state and did fewer bouts of high activity than control tadpoles. Our findings reveal possible ecological effects of microplastics on anurans, as behavioural changes have the potential to influence food capture, predator/prey dynamics, and habitat-use. Future research focusing on linking behavioural findings to changes in energetic and developmental status of the tadpoles will aid in understanding potential physiological mechanisms underlying these behavioural changes.