Laryngeal Demasculinization in Wild Cane Toads Varies with Land Use.

Anthropogenic factors, including the spread of endocrine-disrupting chemicals, have been linked to alterations in the reproductive physiology, morphology, and behavior of wildlife. Few studies of endocrine disruption, however, focus on secondary sexual traits that affect mating signals, despite their importance for reproductive success. The larynx of many anurans (frogs and toads), for example, is larger in males than in females and is crucial for producing mating calls. We aim to determine if wild populations of cane toads (Rhinella marina) near sugarcane fields in Florida have demasculinized larynges when compared to populations near urban areas. We find evidence of demasculinization in both primary and secondary sexual traits in male toads living near sugarcane. Relative to body size, the laryngeal mass, vocal cord length, and dilator muscle width are all reduced in males from sugarcane regions compared to their urban counterparts. Strong correlations between primary and secondary male sexual traits indicate that demasculinization occurs in concert both within and across diverse organs, including the testes, larynx, and skin. Our results show that anurans near sugarcane fields have demasculinized reproductive systems, that this disruption extends to secondary sexual traits like the larynx, and that it is likely due to anthropogenic causes.