GENETIC-VARIABILITY AND DIFFERENTIATION OR HYPOGEAN CYPRINID FISHES FROM SOMALIA

The genetic structure of populations of two hypogean Somali cyprinid s pecies was compared by analysing genetic variation at 30 allozyme loci . The two species, Phreatichthys andruzzii and Barbopsis devecchii, ar e of particular interest, representing two different steps in adaptati on to cave life, as indicated by several morphological features includ ing eye regression. Phreatichthys is completely anophthalmic, while Ba rbopsis shows a highly variable microphthalmia. Results showed a close relationship between Phreatichthys and Barbopsis, suggesting their or igin from a common epigean ancestor. population structure of the two s pecies differs and levels of gene flow are much higher between the Bar bopsis populations than between the Phreatichthys populations. Two pos sible scenarios leading to the current situation are hypothesized.