Cytogenetic analysis of Anopheles ovengensis revealed high structural divergence of chromosomes in the Anopheles nili group

Cytogenetic analysis is an informative classical approach to understanding the relationships among members in a group of closely related species of mosquitoes. Anopheles ovengensis is a recently discovered species of the Anopheles nili group and is one of the important malaria vectors in the African equatorial forest. This study characterized polytene chromosomes of An. ovengensis and compared them with polytene chromosomes of An. nili. Using fluorescent in situ hybridization and chromosome banding pattern comparison we have established correspondence between chromosomal arms of An. ovengensis and An. nili. Analysis of chromosome morphology in the two species revealed a limited similarity in the banding patterns. The most extensive reorganization occurs in pericentromeric and intercalary heterochromatin. Chromosomes of An. ovengensis are joined together by a diffuse chromocenter and they have two large regions of intercalary heterochromatin in arms 2L and 3R. In contrast, the chromocenter and intercalary heterochromatin are not seen in An. nili chromosomes. Comparative analysis of the arm association suggests the occurrence of a whole-arm translocation between the two members of the group. The observed, substantial reorganizations of chromosome structure implies either a rapid rate of chromosome evolution in the An. nili group, or that the two species belong to different taxonomic groups within subgenus Cellia.