GENETIC-DIVERGENCE AMONG MORPHOTYPES OF LAKE TANA (ETHIOPIA) BARBS

The genus Barbus is a paraphyletic assemblage that includes three diff erent ploidy levels: diploid, tetraploid and hexaploid. 'B.' intermedi us, which inhabits Lake Tana (Ethiopia), is a hexaploid taxon that for ms a 'species flock' consisting of at least 14 morphotypes. Thirty-one presumptive allozymic loci were analysed in a large sample of 'B.' in termedius. No diagnostic loci Were observed between the morphotypes, b ut substantial: differences in allele frequencies were found. One morp hotype, Acute, differs significantly from the others. The presence of this genetic differentiation within the lake strongly suggests that th e morphotypes are diverging lineages. Because of some parallel charact eristics with cichlid species flocks, we put forward the hypothesis th at the morphotypes of barbs in Lake Tana represent a species flock tha t originated via sympatric speciation with more rapid morphological th an molecular differentiation. If the differentiation and the reproduct ive isolation are real, it is probable that the morphotypes already ar e or will soon reach the status of species. (C) 1998 The Linnean Socie ty of London.