The Spots of the Spotted Salamander Are Sexually Dimorphic

Abstract

Brilliant and conspicuous coloration in animals is often thought to signal quality to conspecifics (sexual selection) or to signal unpalatability to predators (aposematic selection). Ambystoma maculatum (spotted salamanders) have bilateral rows of conspicuous bright yellow dorsal spots against dark skin. Although this coloration has been long thought a classic example of warning coloration, to date, there are no quantitative measures of spot coloration. We captured adult male and female A. maculatum as they entered breeding ponds and measured body condition, spectral reflectance of the yellow spots, spot size, and coverage of the dorsal area in spots. We found evidence of sexual dichromatism; males had a larger area of their dorsum covered in spots, and tended to have more chromatic, but less bright yellow color. Moreover, our data suggest a tradeoff between coloration and body condition. Animals in better body condition expressed lower chroma and those with greater spot coverage expressed brighter spots ...