The relationship of body colouration to morphological traits in a population of green frogs from Georgia, USA

Sexually dimorphic body colouration can serve to signal quality in vertebrates, but less is known about its importance in amphibians when compared to some other groups. The green frog (Lithobates clamitans) is a common anuran of aquatic habitats in eastern North America. In adults of both sexes, the dorsal abdomen is green or brown, and the ventral abdomen usually white. In contrast, throat colouration is sexually dimorphic; adult male throats are usually bright yellow in colour, whereas females and some males express white throats. We assessed body colouration in males and females from a population in Georgia, USA using spectrophotometry to quantify variation in these features and determine if hidden dimorphism was present. We then asked whether this spectral variation correlated with aspects of phenotype linked to fitness in anurans. Male throats were higher in Green-Yellow Chroma and lower in UV Chroma than those of females, but the sexes did not differ in ventral or dorsal abdominal colour. Male SVL was related to ventral abdominal colouration; larger males tended to have ventral abdomens with longer-wavelength Hue and reduced Green-Yellow Chroma compared to smaller males. However, throat or dorsal abdominal colouration was unrelated to any morphometric trait examined in either sex. Overall, variation in male throat and abdominal colour was only weakly related to indices of male quality; instead, we hypothesize that the persistence of white-throated males in populations throughout the range of green frogs is related to the presence of sex-reversed males and intersex individuals recently described from other populations.