Cytogenetic analyses of Falconiformes have showed that Accipitridae have
atypical chromosomal organization among birds, with relatively low diploid
numbers (mean of 2n=66) and a few pairs of microchromosomes (4 to 6 pairs).
Proposals based on classical cytogenetics suggested that this fact was a result
of fusions of microchromosomes found in the Avian putative ancestor
karyotype. With the aim of contributing to clarify questions concerning
chromosomal evolution and phylogenetics of this family, we analyzed three
species of subfamily Buteoninae (Rupornis magnirostris, Buteogallus
meridionales e Asturina nítida) and two of subfamily Harpiinae (Harpia harpyja e
Morphnus guianensis) by means of classical and molecular cytogenetics.
Buteoninae species showed karyotypes with diploid number 68 and FN varying
from 100 to 102; the number of biarmed chromosomes varied between 17 and
21, Z chromosome was submetacentric and W chromosome was metacentric in
R. magnirostris and submetacentric in Asturina nitida. 18/28 rDNA probes
showed that nucleolar organizer regions are located in a medium-sized
submetacentric pair, corresponding to the short arm of pair 7. Telomeric
sequences were found not only on terminal region of the chromosomes, but
also on some interstitial regions. Whole-chromosome paints derived from pairs
1 to 11 of Gallus gallus (GGA) produced the same number of signals in these
species. The availability of whole-chromosome probes derived of Leucopternis
albicollis confirmed the presence of a common cytogenetic signature for
Buteoninae species, corresponding to the association between GGA1p and
GGA6. An interstitital telomeric sequence found in this pair reinforces this fact.
Concerning the species of Harpiinae, the conventional staining analyses
showed that H. harpyja and M. guianensis have 2n=58 and 2n=56, respectively.
Both species have 22 pairs of biarmed chromosomes, although H. harpyja has
two more chromosomes than M. guianensis. 18/28S rDNA mapped on the short
arm of pair 1 in M. guianensis and in two pairs in H, harpyja (6 and 25).
Telomeric sequences were found on the terminal regions, but also on interstitial
locations in some chromosomes. Despite the apparent karyotypic similarity, no
common associations were found in these two species. The different
associations observed in Morphnus and Harpia indicate that these species
suffered an extensive genomic reorganization after their separation in two
independent lineages. Moreover, the absence of shared associations suggests
that the fissions of macrochromosomes have occurred in the common ancestor
of this group, and that fusions were subsequent to their isolation as different
lineages. Our results, together with previous reports in other species of
Accipitridae, indicate that the processes of fissions involving the
macrochromosomes of GGA and fusions between these segments and
between them and microchromosomes are recurrent rearrangements in this
group. Although Falconidae species also show atypical karyotypes, with low
diploid numbers, global cytogenetic data of Accipitridae indicate that, similarly to
the morphological traits between these two families, the rearranged karyotypes
would correspond to homoplasies, from the evolutionary point of view,
supporting the idea that these families do not form a monophyletic group.
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