Lifecycle exposure to perchlorate differentially alters morphology, biochemistry, and transcription as well as sperm motility in Silurana tropicalis frogs

Highlights: • Western clawed frogs (Silurana tropicalis) were exposed to KClO₄ (0, 20, 53, and 107 μg/L) from fertilized embryo until sexual maturity. • Female growth (e.g., body mass, snout vent length, and hind limb length) was reduced following exposure to KClO₄. • Thyroid hormone- (dio1) and sex steroid-related transcription (srd5α2 and cyp19) were differentially regulated by KClO₄ in ovaries and testes. • KClO₄ altered indices of sperm motility (VAP, VSL, STR, and ALH). • Results suggest that KClO₄ may have indirect secondary effects on the reproductive axes in frogs. Perchlorate (ClO₄⁻) contamination has been reported in ground and surface waters across North America. However, few studies have examined the effects of prolonged exposure to this thyroid hormone disrupting chemical, particularly at environmentally relevant concentrations in lower vertebrates, such as amphibians. The aim of this study was to examine the effects of a yearlong chronic exposure to ClO₄⁻ in adult male and female Western clawed frogs (Silurana tropicalis). Frogs were spawned and raised from fertilized embryo until sexual maturity in potassium perchlorate (KClO₄)-treated water at different concentrations (0, 20, 53, and 107 μg/L). Developmental and reproductive indices – including adult morphology, androgen plasma levels, gonadal thyroid hormone- and sex steroid-related transcript levels, and sperm motility – were evaluated in male and female adult frogs. Female growth (e.g., body mass, snout-vent length, and hind limb length) was significantly reduced following chronic exposure to environmentally relevant concentrations of KClO₄ resulting in females with morphometric indices similar to those of control males – indicating potential sex-specific sensitivities to KClO₄. Changes to reproductive indices (i.e., plasma androgen levels, gonadal thyroid hormone- and sex steroid-related transcript levels, and sperm motility) were also observed in both sexes and suggest that KClO₄ exposure may also have indirect secondary effects on the reproductive axes in male and female adult frogs. These effects were observed at concentrations at or below those reported in surface waters contaminated with ClO₄⁻ suggesting that this contaminant may have developmental and reproductive effects post-metamorphosis in natural amphibian populations.