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.
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We are grateful to N. Anderson, J. Manzano Alvarez, J. Peniston, B. Leavell, and H. Legett for collecting toads; G. Darnell, J. Lam, and E. Terry for assisting with dissections and measurements; and R. Knepp, J. Rusk, and C. Garcia Botero for analyzing photographic data. We are also thankful to K. McCoy, J. Lucas, and S. Johnson for providing valuable advice throughout the project as well as D. Carrillo and G. Nuessly for providing logistical support in Florida. Finally, we thank B. Muller, E. Bledsoe, and E. Khazan for providing comments that improved this manuscript, as well as J. Peniston, for designing figures.
This work was supported by funds from the Department of Biological Sciences at Purdue University to XEB and to SZ (Lindsey Graduate Fellowship) and by a student research grant from the Animal Behavior Society to SZ. SZ was supported by the Purdue Doctoral Fellowship from the Purdue University Graduate School. XEB was supported by the National Science Foundation (IOS #1433990).
Conflict of interest
The authors declare that they have no conflict of interest.
Experiments were approved by the Purdue Animal Care and Use Committee (Protocol #1405001073). All applicable institutional and/or national guidelines for the care and use of animals were followed.
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Zlotnik, S., Gridi-Papp, M. & Bernal, X.E. Laryngeal Demasculinization in Wild Cane Toads Varies with Land Use. EcoHealth 16, 682–693 (2019). https://doi.org/10.1007/s10393-019-01447-x
- Anuran amphibian
- Mating signal
- Endocrine disruptor
- Vocal cords
- Rhinella marina (Bufo marinus)