Cytotaxonomy of the Simulium damnosum complex from central and northeastern Tanzania

A cytotaxonomic study of the medically important insect vector, Simulium damnosum s.l., revealed the presence of seven and possibly eight distinct taxa from central and northeastern Tanzania. Larval salivary gland polytene chromosome maps are presented for the first time for five cytotypes and one sibling species, which include the Nkusi form, the Sanje form, the Kisiwani form, Ketaketa C1 and C2, and the Kibwezi form. Inversion disequilibrium in males of the Kibwezi form indicate population substructuring is occurring and that this population may be in the early stages of speciation. Adults of the sibling species S. damnosum Kibwezi form and cytotype of the S. damnosum Nkusi form were identified using Malpighian tubule polytene chromosomes. The taxonomic status of the populations under study are discussed in relation to previously published papers and unpublished reports. Dimorphisms for centromere band enhancement occur on all three polytene chromosomes of the complement. The same centromere band can be polymorphic, sex linked, fixed, or lost in various cytotypes. In constructing a partial phylogeny, a hypothetical intermediate is proposed to account for the diverse fate of these centromere band dimorphisms and other inversion polymorphisms in different members of this nearly pan African complex. This pattern of chromosome restructuring is consistent with that seen for other species complexes within the Simuliidae.