Male hind leg waving is involved in chemical communication during courtship in the African Dwarf Clawed Frog

In contrast to other vertebrate classes, few pheromones have been identified and characterized in amphibians. One of the species in which chemical communication has already been demonstrated is the fully aquatic African Dwarf Clawed Frog Hymenochirus boettgeri (Anura, Pipidae). Males of this species have a subdermal breeding gland behind each front leg, which substantially enlarges when they are sexually active and calling. It has been shown in a Y-maze experiment that females are attracted to males with breeding glands, but not to males where the breeding glands are surgically removed. However, other potential functions during courtship remain unknown and the molecules involved are still unidentified. To better understand the function of the breeding gland, we studied and filmed in detail the courtship behaviour of Hymenochirus boettgeri. We observed that during courtship, males often wave their hind legs to the female before engaging in amplexus. This waving transfers water from around the breeding glands, and therefore any water-soluble chemical produced by them, directly towards the female's nose. Chemical analysis of water taken from the male's direct proximity during this behaviour confirms the presence of water-soluble molecules. Our study thus indicates the presence of short-distance chemical communication during courtship in natural conditions. We are currently using an integrative approach combining a cDNA library of the breeding gland, chemical analysis of water, and more fine-tuned behavioural assays to further characterize the key molecules in this waving behaviour.