III‐Cytogenetic and molecular genetic data

Abstract

Cyprinid fishes assigned to the genus Barbus constitute a poly‐phyletic assemblage that includes at least three different ploidy levels: diploid, tetraploid and hexaploid. ’B. ‘ intermedius, inhabiting Lake Tana (Ethiopia), is a hexaploid taxon that forms a ‘species flock’ consisting of at least 14 morphotypes. The phenomenon is described in this review with reference to currently available cytogenetic and molecular genetic data. Cytogenetic data show that ’B. ‘ intermedius is hexaploid both within and outside the Lake Tana basin. No chromosome banding analyses are currently available. Data based exclusively on conventionally Giemsa‐stained chromosomes suggest interpopulation variability. This should be confirmed using chromosome banding techniques. Major Histocompatibility Complex genes sequencing gave the first indication of genetic isolation of morphotypes. Allozymes have been analysed in a large sample of ’B.’ intermedius. No diagnostic loci were observed in the ’B.’ intermedius morphotypes, but more or less important differences in allele frequencies were found. Only one morphotype, Acute, differs significantly from the others. The presence of this genetically differentiated morphotype in the lake strongly suggests that the morphotypes are diverging lineages. Because of some parallel characteristics with cichlid species flocks, we put forward the hypothesis that the barb morphotypes in Lake Tana represent a species flock that originated via sympatric speciation with more rapid morphological than cytogenetic and molecular differentiation. If the differentiation 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.