Exposure of tadpoles to bisphenol A and ethinylestradiol does not influence the behaviour of frogs in the tonic immobility test

Endocrine-disrupting compounds (EDCs), such as bisphenol A (BPA) and ethinylestradiol (EE2), are widespread pollutants that can interfere with the action of endogenous hormones and thus affect the development and behaviour of animals. However, our current understanding of the impact of EDCs on amphibian behaviour remains limited. The aim of this study was to investigate whether exposure of the marsh frogs Pelophylax ridibundus tadpoles to BPA or EE2 influences their behaviour after metamorphosis in the tonic immobility (TI) test. EDCs concentrations were adjusted to environmentally relevant levels observed in surface waters in Europe (BPA at 1 × 10−7 M and EE2 at 1 × 10−9 M). Exposure lasted from the free-swimming stage (Gosner stage 21) to the beginning of tail atrophy (around Gosner stage 43). The control group consisted of tadpoles kept in carbon-filtered tap water, devoid of EDCs. Altogether, 150 juvenile frogs (60 exposed to EE2, 60 exposed to bisphenol A, and 30 control ones) were tested for TI. Body temperatures were recorded before and after the test. Morphometric measurements (body length and mass) and sex identification were performed post-mortem. The exposure to BPA or EE2 and frog sex did not affect TI duration. Body condition, expressed as body mass index, had a marginally significant negative effect, whereas body temperature had a marginally positive effect on TI duration. Moreover, body temperature decrease during a series of three trials was positively related to the total TI duration. Thus, our results suggest that currently typical environmental levels of BPA and EE2 do not influence the TI reaction in frogs. However, the effects of body condition and temperature warrant further research.