INTRA-SPECIFIC HETEROGENEITY OF THE RDNA INTERNAL TRANSCRIBED SPACER IN THE SIMULIUM-DAMNOSUM (DIPTERA, SIMULIIDAE) COMPLEX

The internal transcribed spacer (ITS) of the rRNA gene cluster has bee n used as a model for the study of the action of concerted evolution a nd molecular drive on repeated sequence families. In contrast to this general finding, preliminary DNA sequence analysis of cloned represent atives of the ITS from the West African black fly species complex Simu lium damnosum s.l. demonstrated extensive intra-individual and intra-s pecific polymorphisms. Variability in the ITS was primarily confined t o the ITS1 domain. The degree and type of intra-individual and intrasp ecific variability within the ITS was further characterized using gel electrophoresis, DNA hybridization, and heteroduplex analysis of the P CR products generated from the ITS1 domain. ITS1 copies from individua l S. damnosum s.l. differed in length and sequence composition. These results, when taken together, demonstrate that a large degree of intra -individual and intra-specific heterogeneity exists in the ITS of S. d amnosum s.l. The intra-individual heterogeneity was greater in the sav anna-dwelling than forest-dwelling sibling species of S. damnosum s.l. This heterogeneity may be due in part to inter-breeding among sympatr ic sibling species, coupled with disturbance of S. damnosum s.l. popul ations resulting from intensive vector control efforts.