Characterization of the atypical karyotype of the black-winged kite Elanus caeruleus (Falconiformes: Accipitridae) by means of classical and molecular cytogenetic techniques

The karyotype of the black-winged kite (Elanus caeruleus), a small diurnal raptor living in Africa, Asia and southern Europe, was studied with classical (G-, C-, R-banding, and Ag-NOR staining) and molecular cytogenetic methods, including primed in-situ labelling (PRINS) and fluorescence in-situ hybridization (FISH) with telomeric (TTAGGG) and centromeric DNA repeats. The study revealed that the genome size, measured by flow cytometry (3.1 pg), is in the normal avian range. However, the black-winged kite karyotype is particularly unusual among birds in having a moderate diploid number of 68 chromosomes, and containing only one pair of dot-shaped microchromosomes. Moreover, the macrochromosomes are medium-sized, with the Z and W gonosomes being clearly the largest in the set. C-banding shows that constitutive heterochromatin is located at the centromeric regions of all chromosomes, and that two pairs of small acrocentrics and the pair of microchromosomes are almost entirely heterochromatic and G-band negative. The distribution pattern of a centromeric repeated DNA sequence, as demonstrated by PRINS, follows that of C-heterochromatin. The localization of telomeric sequences by FISH and PRINS reveals many strong telomeric signals but no extratelomeric signal was observed. The atypical organization of the karyotype of the black-winged kite is considered in the context of the modes of karyotypic evolution in birds.