Testing the phenotype-linked fertility hypothesis in male Moor Frogs (Rana arvalis) exhibiting a conspicuous nuptial colouration

The conspicuous blue nuptial colouration of Moor Frog (Rana arvalis) males has been associated with sexual selection; it may provide females with information about benefits to be gained through mate choice. Here we investigated the phenotype-linked fertility hypothesis suggesting that exaggerated traits may advertise fertilization ability. We evaluated conspicuousness of males' colouration and related this to the number of sperm stored in their testes. Contrary to our expectation, we did not find a positive relationship between blueness of males and the number of sperm stored in the testes. We discuss this result in the light of alternative traits that may be advertised by colouration, such as sperm quality or good genes for offspring survival. We now need direct studies of female mate choice and the physiology of the blue nuptial colouration to clarify the evolutionary background of the striking temporal sexual dichromatism in the Moor Frog.