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Mystery of Chironomus dorsalis Meigen karyotype (Diptera: Chironomidae)

Kiknadze I.I., Golygina V.V., Broshkov A.D., Gunderina L.I., Istomina A.G.

Abstract. The study of the karyotype structure of Chironomus dorsalis Meigen, 1818 from the “pseudothummi” cytocomplex was performed. Arms C and D were mapped for the first time according to Keyl-Dévai system (Keyl, 1962; Dévai et al., 1989) in addition to arms A, E, and F, mapped by Keyl (1962). The structure of the centromeric regions of Ch. dorsalis has been described in more detail and compared with the reference species, Ch. piger Strenzke, 1959, and the other species of the “thummi” cyto-complex. It was discovered that Ch. dorsalis karyotype differs clearly from other Chironomus species by the banding pattern of centromeric regions on the chromosomes AE and BF. Two thick C-positive bands are located on the centromeric region of each of these chromosomes. The hypothesis was suggested that chromosomes AE and BF of Ch. dorsalis are dicentric with one active centromere. The data obtained also support previously postulated hypothesis that the “pseudothummi “ cytocomplex should be considered as more primitive and ancestral to other cytocomplexes of the genus Chironomus Meigen, 1803. Natural populations of Ch. dorsalis from various regions of Russia were studied for the ?rst time as well the chromosomal polymorphism in some of these populations was quantitatively estimated that allowed us to assess the size of banding sequence pool for this species, which consists of 8 banding sequences.