Molecular diversity and phylogenetic relationships of the gastropod genus Melanoides in Lake Malawi
The freshwater snails belonging to the genus Melanoides Olivier, 1804 are widespread across tropical regions of the world and endemic species have evolved in the African Lakes Malawi, Mweru and Tanganyika. The endemic Melanoides species of Lake Malawi have been investigated several times during the last century, due to their large conchological variation, but no unambiguous answer regarding the number of species has been given. The phylogenetic relationship between morphs or genetic clones of Melanoides in Lake Malawi was inferred by phylogenetic analyses of DNA sequence data from the mitochondrial genes 16S and COI. Additional sequences from GenBank were included to investigate the relationship to other morphs from different parts of the world. For the first time, a putative secondary structure was developed for a partial region of 16S in this genus to identify the variability of the secondary structure in stems and loops. The molecular analyses indicated that several genetic clones exist in Lake Malawi and that M. tuberculata is a paraphyletic taxon. It is not clear from the results whether invasions or dispersals account for the complex situation in Lake Malawi. The basal position of M. admirabilis, endemic to Lake Tanganyika, in the inferred phylogeny indicates that Africa might be the origin of the genus. The results further indicate that three major clades of Melanoides,consisting of several genetic clones, are present in Lake Malawi; one clade consisting of invasive M. tuberculata, another of native M. tuberculata and a third consisting of the M. polymorpha-complex. It appears as if the unique development of morphs within the Melanoides genus in Lake Malawi has evolved primarily by divergence of genetic clones instead of species differentiation.
Keywords: Melanoides, Lake Malawi, 16S, COI, phylogenetic relationships