1 1Konrad Lorenz Institute for Ethology, Austrian Academy of Sciences, Savoyenstrasse 1A, 1160 Vienna, Austria; Behavioural Ecology Group, Department of Systematic Zoology and Ecology, Eötvös Loránd University, Pázmány
Péter sétány 1/C, 1117 Budapest, Hungary
2 2Biometry and Population Biology Research Group, Center for Evolutionary and Functional Ecology, 1919 Route de Mende, 34293 Montpellier, France
3 3Ecological Genetics Research Unit, Department of Biological and Environmental Sciences, University of Helsinki, P.O. Box 65, 00014 Finland
4 4Behavioural Ecology Group, Department of Systematic Zoology and Ecology, Eötvös Loránd University, Pázmány Péter sétány 1/C, 1117 Budapest, Hungary; Ecological Genetics Research Unit,
Department of Biological and Environmental Sciences, University of Helsinki, P.O. Box 65, 00014 Finland
5 5Department of Population Biology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18 d, 75236 Uppsala, Sweden
Variation in colouration has rarely been related to sexual selection in anuran amphibians, even though such a relationship has been proven for many other vertebrate taxa. Male and female Moor Frogs (Rana arvalis) have a cryptic brown colour pattern, but males develop a conspicuous blue nuptial colouration during the reproductive season. To investigate the possibility that colouration plays a role in sexual selection in this species, we studied the temporal variation in blue colouration, determined if body size or body temperature affected blueness and investigated if blueness of males could be related to their mating success. Results confirmed previous observations that males develop and maintain blue colouration for only a very few nights during peak reproductive activity. Colouration of males was unrelated to body size, but males exhibiting higher body temperatures were somewhat bluer than males with lower body temperatures. Further, males in amplexus had higher body temperatures than non-mated males. Finally, mating success was positively related to blueness in small males, whereas in large males no such relationship was detected. While our results align with the hypothesis that the bright blue colouration of males may be a target of sexual selection, alternative explanations are also discussed.