Effect of ethylenethiourea on metamorphosis and ovary development: A comparative study of three larval frogs

Abstract

Amphibian endocrine systems interact with each other during normal development.Interference with one of the endocrine systems may influence others. We studied the effect of a thyroid inhibitor (ethylenethiourea [ETU]) on metamorphosis and ovary development of three species, Sphaerotheca pashchima, Indosylvirana caesari, and Euphlyctis cyanophlyctis with different larval durations. We treated the tadpoles of these species with 50, 100, and 200 mg/L concentrations of ETU and studied their larval duration, size at metamorphosis, and ovary development. The results revealed that ETU affects metamorphosis, depending on the species and concentration. ETU delayed metamorphosis of E. cyanophlyctis tadpoles and did not affect metamorphosis in S. pashchima tadpoles. Lower concentrations of ETU stimulated metamorphosis in I. caesari tadpoles while high concentration delayed metamorphosis. In the tadpoles (E. cyanophlyctis) treated with higher concentrations of ETU, ovary development was advanced with an increased size of the diplotene oocytes. Oocyte size was smaller in the tadpoles (of I. caesari) treated with lower concentrations of ETU. These results demonstrated that the tadpoles of these species show different responses to the thyroid inhibitor, possibly due to the differences in the larval duration and sensitivity. Inhibition or acceleration of metamorphosis did not interfere in the ovary development of E. cyanophlyctis and I. caesari. These results will be useful in understanding the impact of endocrine disruptors on the interaction between thyroid and sex steroid hormones.

Phenotypic Variation Through Ontogeny: Thyroid Axis Disruption During Larval Development in the Frog Pleurodema borellii

“…Furthermore, methimazole did not delay differentiation or inhibit metamorphosis; on the contrary, it was observed individual differences, with some tadpoles reaching metamorphosis while others have just reached premetamorphic states. Phuge et al (2021) reported the ethylenethiourea (a thyroid inhibitor) did not affect metamorphosis in Sphaerotheca pashchima and at lower concentrations stimulated metamorphosis in the anuran Indosylvirana caesari, and suggested differences in the larval development duration and sensitivity. Our experiments revealed that the stage at which exposure started had an impact on larval differentiation, since tadpoles exposed earlier to methimazole reached metamorphosis whereas tadpoles exposed later remain in prometamorphosis.…”