Lake Tanganyika endemic gastropods also occur in the Lukuga River

Abstract

Ancient lakes with their endemic species assemblages, like Lake Tanganyika in East Africa, are regarded as hotspots of aquatic biodiversity and as natural laboratories providing insights into evolutionary processes, such as intra-lacustrine speciation. The origin of the gastropod species super flock in Lake Tanganyika has been debated intensively and remains unclear to date. For the fish community, it is generally assumed that it was derived from ancestors occurring in the Congo River Basin. Recently, a central biogeographical role of the Lukuga River system and the connected Lualaba River has been indicated. In an attempt to trace the origin of the enigmatic thalassoid gastropods of Lake Tanganyika, the fauna of the Lukuga-Lualaba systems is currently being studied. A recent expedition allowed collecting mollusc material from the eastern shores of Lake Tanganyika around Kalemie and down the Lukuga River until Niemba. We found gastropods known to be endemic to Lake Tanganyika living in the Lukuga River as far down as 95 km, in populations with reasonable abundances. Based on mitochondrial DNA sequences, these populations are partially genetically distinct from Lake Tanganyika’s populations. However, sister taxa to the species flock have not yet been found in the Lukuga River. Our results are discussed in the context of intra-riverine evolutionary dynamics over shorter time periods. They will also help to understand the biogeographical and evolutionary dynamics within a large spatial and temporal framework, covering Lake Tanganyika and the Congo River system.