The 'Barbus' intermedius species flock in Lake Tana (Ethiopia): III - Cytogenetic and molecular genetic data

Cyprinid fishes assigned to the genus Barbus constitute a polyphyletic asse mblage that includes at least three different ploidy levels: diploid, tetra ploid and hexaploid. 'B.' intermedius, inhabiting Lake Tana (Ethiopia), is a hexaploid taxon that Forms a 'species flock' consisting of at least 14 mo rphotypes. The phenomenon is described in this review with reference to cur rently available cytogenetic and molecular genetic data. Cytogenetic data s how that 'B.' intermedius is hexaploid both within and outside the Lake Tan a basin. No chromosome banding analyses are currently available. Data based exclusively on conventionally Giemsa-stained chromosomes suggest interpopu lation variability. This should be confirmed using chromosome banding techn iques. Major Histocompatibility Complex genes sequencing gave the first ind ication of genetic isolation of morphotypes. Allozymes have been analysed i n a large sample of 'B.' intermedius. No diagnostic loci were observed in t he 'B.' intermedius morphotypes, but more or less important differences in allele frequencies were found. Only one morphotype, Acute, differs signific antly from the others. The presence of this genetically differentiated morp hotype in the lake strongly suggests that the morphotypes are diverging lin eages. Because of some parallel characteristics with cichlid species flocks , we put forward the hypothesis that the barb morphotypes in Lake Tana repr esent a species flock that originated via sympatric speciation with more ra pid morphological than cy togenetic and molecular differentiation. If the d ifferentiation and the reproductive isolation (at least partial) are real, it is probable that the morphotypes already are and/or soon will reach the status of species.