Postmetamorphic retention of a lateral line system in African slippery frogs (Amphibia: Anura: Conraua)

Abstract

Adult anurans normally lose their larval lateral-line (LL-)system during metamorphosis. Only some species with an extensive aquatic life style (e.g., Bombina bombina, all pipid frogs) are known to retain that system as adults. The aquatic African Slippery Frogs, genus Conraua, have never been studied for this system. We examined adults of all known Conraua species and tadpoles of six species from this genus for the occurrence of LL-systems. We detected a LL-system in all tadpoles studied, in adults of all West African species (C. alleni, C. derooi, C. kamancamarai, C. sagyimase, C. sp.), as well as in adults of the East African C. beccarii. In contrast we found no LL-systems in adult C. crassipes, C. goliath, and C. robusta from Central Africa. The tadpoles exhibited a LL-system typical for anurans with free-swimming larvae. In particular it was morphologically congruent to other stream tadpoles. Topography and histology of neuromasts in adults indicates their larval origin. Neuromast abundance, topography and histology, may allow Conraua a complex access to spatial information. However, although all species of the genus are aquatic, only two-thirds of them retain a postmetamorphic LL-system. In both major clades within the monophyletic genus we detected species with and without a LL-system. We hypothesize that the ancestor of current Conraua retained the larval LL-system, and that it was aquatic and lived in non or little torrent sections of forest rivers and streams. Those Central African species which live in particularly torrent streams, C. goliath and C. robusta, probably lost the LL-system. Conraua crassipes, which today lives in slow flowing streams, may have had ancestors with a torrenticulous lifestyle.