Morphological and genetic differentiation of 11 populations of the African catfishChrysichthys nigrodigitatus(Siluroidei; Claroteidae), with consideration of their biogeography

Abstract

Eleven samples of Chrysichthys nigrodigitatus and one sample of C. maurus were studied using morphometrics and enzyme polymorphism. Samples from opposite areas in the range of the species were most differentiated morphologically (Dagana in Senegal and Selingue in Mali, on one hand, and Bas Kouilou in Congo, on the other hand). In the sample from Bas Kouilou, most specimens overlap those from Ebrie Lagoon in Côte d'Ivoire. The populations from Côte d'Ivoire are genetically the most variable and have the highest number of alleles in common with the sample of C. maurus (ancestral alleles). The samples from the limits of the species' range (Dagana, Bas Kouilou) are those that have the least polymorphism (both monomorphs) and the fewest alleles in common with C. maurus. On the basis of these results we present a hypothetical scenario for the colonization of basins by populations of C. nigrodigitatus after the last glaciation. Colonization started in the area between Côte d'Ivoire and Benin. From this region of origin, some populations colonized the basins to the west via the coastal area up to Senegal. Independently, other populations colonized the basins to the east via the coastal area up to Zaïre. The colonization of the Niger most likely occurred through its Lower Delta.