Effects of Endocrine Disruptors Ethinylestradiol and Procloraz on the vocal system of the frog Xenopus tropicalis

 

Prochloraz masculinizes the larynx of female Xenopus tropicalis

 

Endogenous sex steroids are not only important for sexual differentiation in amphibians, but also for the development of secondary sex characteristics. The advertisement call of male frogs is used to attract females and in male-male competitive interactions. The call is associated with larger more numerous neural and muscular structures of sound production. The vocalization system of Xenopus and other Pipid frogs, the larynx and associated structures, is extremely sexual dimorphic. This includes both gross morphology such as size and shape of the larynx and other structures in the vocal pathway but also properties of the laryngeal muscles such as twitch type, enzymatic activity, dynamic properties, efficacy of the laryngeal synapses of the laryngeal neuromuscular junction, and the number of laryngeal motor neurons and axons and their properties. The sex differences in the vocal system develop during pre- and post-metamorphic stages under the influence of the sex steroids, mainly androgens. The extreme androgen-sensitivity of the larynx and the neurons which control vocal behaviour in Xenopus frogs provide a powerful experimental system for studying the effects of endocrine disruptors on sexual differentiation. We exposed tadpoles and metamorphs of the species Xenopus tropicalis to the synthetic estrogen ethinylestradiol and the fungicide prochloraz. Prochloraz masculinized the larynx of female frogs while ethinylestradiol had no effect. Masculinization of the vocal system of females may disrupt reproduction and subsequent the population dynamics.