Colouration matters in dull toads: ultraviolet adornment for ladies and agrochemicals fading effects

Integument colouration can influence many aspects of fitness, and is under strong sexual selection. Amphibians often express sexual dichromatism, and ultra-violet (UV) colouration is usually biased toward males as a sexual signal. As an honest signal, colouration is related to several individual traits, but can also be related to environmental factors such as anthropogenic pollutants, to which amphibians are highly sensitive. In this study, we investigated sexual dichromatism and UV reflectance covering a large visual spectrum (wavelength ranging from 300 to 700 nm) on different body areas (throat, ventral and dorsal areas), in a widespread amphibian species, the spiny toad (Bufo spinosus). Then, we tested the impact of chronic exposure to two widespread herbicides (glyphosate’s primary metabolite [AMPA] and Nicosulfuron) on their colouration. We found a strong but unexpected sexual dichromatism with females reflecting more in the UV spectrum (throat and ventral area) than males, suggesting these body parts might be critical in intra-specific signalling. Females with higher ventral UV reflectance were in better body condition, suggesting an honest signal role of UV reflectance which could influence male choice. Throat colouration was further differentially influenced by agrochemicals according to sexes. In AMPA-exposed males, throat was more saturated in yellow-orange than in control males, and Nicosulfuron exposure decreased the throat’s reflectance hue in females, which can bear consequences on mate attractiveness. Future studies need to investigate the underlying mechanisms that are altered by agrochemical exposure.


Amphibians, Honest signal, AMPA, Nicosulfuron, Sexual dichromatism

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Appendix A : Reflectance spectrum in female (turquoise bracket) and male (coral bracket) spiny toads (Bufo spinosus, n = 81).
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Appendix B : Correlations between the Principale Components (PCs) 1 and 2, and the different fractions of reflectance included in the PCA: hue, UV-saturation, UV-luminance, total brightness ...
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Appendix C : Relationships between reflectance PCA scores and body condition or sex in spiny toads (Bufo spinosus). Values are estimates obtained from linear regressions. ...
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Supplementary file4
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Supplementary file5
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Author's final draft
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How to cite
Tartu Sabrina, Lorrain-Soligon Léa, Cheron Marion, Dupoué Andreaz, Brischoux François (2023). Colouration matters in dull toads: ultraviolet adornment for ladies and agrochemicals fading effects. Oecologia. 203. 491-502.,

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