Most Neotropical Psittacidae have a diploid number of 2n=70, and a dichotomy in chromosome patterns. Long-tailed species have biarmed macrochromosomes, while short - tailed ones have telo/acrocentric macrochromosomes. However, the use of chromosome painting with chicken and white hawk probes has demonstrated that karyotype evolution in Psittacidae includes a high number of inter/intrachromosomal rearrangements. Hence, to determine the phylogeny of Long and Short-Tailed species, and to propose a putative ancestral karyotype for this group, we constructed homology maps of Pyrrhura frontalis (PFR) and Amazona aestiva (AAE) and compared them to other previously analyzed long-tailed species. Chromosomes were analyzed by conventional staining and fluorescent in situ hybridization (FISH) using whole chromosome paints of G. gallus (GGA) and L. albicollis (LAL). Conventional staining showed a karyotype with 2n=70 in both species, with biarmed macrochromosomes in Pyrrhura frontalis and telo/acrocentric chromosomes in Amazona aestiva. Comparison of the results with the putative avian ancestral karyotype (PAK) showed fusions in P. frontalis of PAK1p/PAK4q (PFR1) and PAK6/PAK7 (PFR6) with a paracentric inversion in PFR6. However, in A. aestiva there was only the fusion between PAK6/7 (AAE7) with a paracentric inversion. Hybridizations with LAL probes confirmed these results. The results indicate that PFR retained a more basal karyotype than Anodorhynchus hyacinthinus (AHY), Ara macao (AMA) and Ara chloropterus (ACH), because these three species show the fusion PAK8/PAK9 that is not seen in PFR. Hence, we suggest that the ancestral karyotype of species with biarmed chromosomes have the fusions PAK1p/PAK4 and PAK6/PAK7 and, additionally, a pericentric inversion of PAK6/PAK7, while the fusion PAK8/PAK9 would have appeared in the common ancestor of Anodorhynchus hyacinthinus, Ara macao and Ara chloropterus. However, the species A. aestiva shows a characteristic plesiomorphic trait, since PAK1p/PAK4q and PAK8/9 fusions are absent. Our results base on chromosome rearrangements suggest the classification following the criterium of tail length may no reflect the real phylogenetic history of Neotropical Psittacidae.

Avian sex chromosomes evolved after the divergence birds and crocodilians from their common ancestor, so they are much younger than the better-studied chromosomes of mammals. It has long been recognized that there may have been several stages to the evolution of avian sex chromosomes. For example, the CHD1 undergoes recombination in paleognaths but not neognaths. Genome assemblies have suggested there may be variation in the timing of barriers to recombination among Neognathae, but there remains little understanding of the extent of this variability. Here, we look at partial sequences of ATP5F1A, which is on the avian Z and W chromosomes. It is known that recombination of this gene has independently ceased in Galliformes, Anseriformes, and at least five neoavian orders, but whether there are other independent cessations of recombination among Neoaves is not understood. We used a combination of data extracted from published chromosomal-level genomes with data collected using PCR and cloning to identify Z and W copies in 22 orders. Our results suggest there may be at least 19 independent cessations of recombination within Neognathae, and 3 clades that may still be undergoing recombination (or have only recently ceased recombination). Analyses of ATP5F1A protein sequences revealed an increased amino acid substitution rate for W chromosome gametologs, suggesting relaxed purifying selection on the W chromosome. Supporting this hypothesis, we found that the increased substitution rate was particularly pronounced for buried residues, which are expected to be more strongly constrained by purifying selection. This highlights the dynamic nature of avian sex chromosomes, and that this level of variation among clades means they should be a good system to understand sex chromosome evolution.