Exposure, but not timing of exposure, to a sulfonylurea herbicide alters larval development and behaviour in an amphibian species
Abstract
Environmental contamination is one of the major causes of biodiversity loss. Wetlands are particularly susceptible
to contamination and species inhabiting these habitats are subjected to pollutants during sensitive phases of
their development. In this study, tadpoles of a widespread amphibian, the spined toad (Bufo spinosus), were
exposed to environmental concentrations of nicosulfuron (0 μg/L; 0.15 ± 0.05 μg/L and 0.83 ± 0.04 μg/L), a
sulfonylurea herbicide, during different phases of development. Tadpoles were exposed during embryonic (12.98
± 0.90 days) or larval development (93.74± 0.85 days), or throughout both phases, and we quantified development
duration, morphological traits and behavioural features as responses to exposure. Developing tadpoles
exposed to nicosulfuron were larger, but with smaller body, and had shorter but wider tail muscles. They were
also more active and swam faster than control tadpoles and showed diverging patterns of behavioural
complexity. We showed that higher concentrations had greater effects on individuals than lower concentrations,
but the timing of nicosulfuron exposure did not influence the metrics studied: Exposure to nicosulfuron triggered
similar effects irrespective of the developmental stages at which exposure occurred. These results further indicate
that transient exposure (e.g., during embryonic development) can induce long-lasting effects throughout larval
development to metamorphosis. Our study confirms that contaminants at environmental concentrations can have
strong consequences on non-target organisms. Our results emphasize the need for regulation agencies and policy
makers to consider sublethal concentrations of sulfonulyrea herbicides, such as nicosulfuron, as a minimum
threshold in their recommendations.