Widespread geographic distribution of mitochondrial haplotypes in rockdwelling cichlid fishes from Lake Tanganyika

The spectacularly diverse cichlid fish species flocks of the East African Rift Lakes have elicited much debate on the potential evolutionary mechanisms responsible for the origin of these adaptive radiations. An historical perspective on population structure may offer insights into the processes driving population differentiation and possibly speciation. Here, we examine mitochondrial DNA (mtDNA) sequence variation in two endemic species of rock-dwelling cichlids, Simochromis babaulti and S. iliagramma, from Lake Tanganyika. Phylogeographic analyses were used to infer what factors might have been important in the genetic structuringof Simochromis popalations. Patterns of mtDNA dif-ferentiation in Simochromis were compared to those of other rock-dwelling cichlids to distinguish befween competing hypotheses concerning the processes underlying their evolution. In striking contrast to previous findings, populations of. Simochromis, even those separated by up to 300 km, were found to share mitochondriat DNA haplotypes. There is no conespondence between mtDNA genealogies and the geographical distribu-tion of populations. Only S. babaulti, but not S. diagramma was found to have a signifi