A new nomenclature for the chromosome-specific probes of white hawk (Leucopternis albicollis)

The white hawk (Leucopternis albicollis) is a diurnal bird of prey (Accipriformes, Accipitridae). This species has a karyotype with a low diploid number (2n=66), however, the comparison with Gallus gallus (2n=78) and the putative avian ancestral karyotype indicates the occurrence of extensive chromosome fissions in the ancestral macrochromosomes. Hence, it is likely that fusions involving microchromosomes underly the decrease in the diploid number in the white hawk. Considering that the ancestral macrochromosomes are fissioned, the chromosome-specific probes made for each of the chromosome segments resulting from the fissions allow the detection of intrachromosomal rearrangements in species with conserved karyotype. Using this strategy, whole chromosome probes from the white hawk have been exploited as a cytogenetic tool for phylogenetic studies in birds since 2010. However, some problems were detected with this first set of probes. Here, we have constructed new probes of the white hawk in order to improve the previous set. Additionally, we have employed bacterial artificial chromosome (BAC) hybridization for chromosome 17-28 to confirm the expected microchromosome fusions. Our results show that microchromosomes 17-28 were involved in fusion events with macrochromosomes. In addition, a new nomenclature has been proposed for the new set of probes and some previous inaccuracies corrected. As an example, ancestral chromosome GGA1 is now shown to have homology to seven white hawk chromosomes rather than five, as homologies to two small chromosomes were missed. In conclusion, the new complete set of chromosome probes will improve the value of this tool for avian comparative cytogenetics.