Chromosomal Mapping of Repetitive DNAs in <b><i>Myiopsitta monachus</i></b> and <b><i>Amazona aestiva</i></b> (Psittaciformes, Psittacidae) with Emphasis on the Sex Chromosomes

Abstract

Here, for the first time, we describe the karyotype of Myiopsitta monachus (Psittacidae, Arini). We found 2n = 48, corresponding to the lowest diploid number observed in Neotropical Psittaciformes so far, with an uncommonly large W chromosome homomorphic to the Z. In order to better understand the evolution of the sex chromosomes in this species, we applied several molecular cytogenetic approaches, including C-banding, FISH mapping of repetitive DNAs (several microsatellite repeats), and whole-chromosome painting on metaphases of M. monachus. For comparison, another species belonging to the same tribe but with a smaller W chromosome (A. aestiva) was also analyzed. The results show that the constitutive heterochromatin has a very diverse distribution pattern in these species revealing heterochromatic blocks in the centromeric region of all chromosomes and in most of the length of the W chromosome in A. aestiva, while in M. monachus they were found in interstitial and telomeric regions. Concerning the microsatellites, only the sequence (CG)_n produced signals on the W chromosome of A. aestiva, in the distal region of both arms. However, in M. monachus, (CAA)_n, (CAG)_n, and (CG)_n probes were accumulated on the W chromosome, and, in addition, the sequence (CAG)_n also hybridized to heterochromatic regions in macrochromosomes, as well as in microchromosomes. Based on these results, we suggest that the increase in length of the W chromosome in M. monachus is due to the amplification of repetitive elements, which highlights their significant role in the evolutionary process of sex chromosome differentiation.

Repetitive DNAs and shrink genomes: A chromosomal analysis in nine Columbidae species (Aves, Columbiformes)

“…In addition, our data reinforced the view that the existence of one pair of microchromosomes bearing 18S rDNA clusters is apparently an ancestral character retained in Columbidae, and that repetitive sequences did preferentially accumulate in the centromeric regions of macro and microchromosomes, as well as in the W chromosomes. Additionally, despite the fact that studies with repetitive sequences in birds are still incipient, the comparison of our data with the ones for Psittaciformes, Piciformes and Galliformes ( Matsubara et al , 2015 ; de Oliveira et al , 2017 ; Furo et al , 2017 ) shows interesting variation in accumulation sites for some of them, reinforcing microsatellites as important markers for studies on karyotype evolution.…”

“…, 2010 ; Kretschmer et al. , 2014 , 2015 ; dos Santos 2015 , 2017 ). Interestingly, while (GGA) 10 produced signals in pair 2 of Zenaida auriculata , this sequence did not produce any signal in the two species of the genus Geotrygon .…”

“…Recently, distinct hybridization patterns of microsatellite sequences have been demonstrated in species of two different orders of birds ( de Oliveira et al , 2017 ; Furo et al , 2017 ). In Piciformes, a large accumulation of 10 sequences was observed on autosomes and especially on the Z sex chromosome in three woodpecker species (Picidae).…”

“…The Z chromosome corresponds to the larger element of their karyotype due to the accumulation of such sequences, which increased its size ( de Oliveira et al , 2017 ). On the other hand, in Myiopsitta monachus (Psittaciformes, Psittacidae) these sequences accumulated preferentially in the W sex chromosome, which has the same size of the Z chromosome, unlike most Neognathae bird species ( Furo et al , 2017 ). These two examples show that the analysis and mapping of repetitive sequences in the genome of avian species may contribute for a better understanding of the processes underlying sex chromosomes differentiation and karyotype evolution.…”

Chromosome Painting in Tyrant Flycatchers Confirms a Set of Inversions Shared by Oscines and Suboscines (Aves, Passeriformes)

“…Most birds have been shown to possess constitutive heterochromatin concentrated in the pericentromeric regions and, as a rule, in the W chromosome. The exceptions so far are related to the enlargement of sex chromosomes, such as in Piciformes and in Myiopsitta monachus de Oliveira Furo et al, 2017] and in species of New World vultures [Tagliarini et al, 2007[Tagliarini et al, , 2009. With regard to telomeric sequences, it was observed that some species of birds show numerous interstitial telomeric sequences, especially in Ratites [Nanda et al, 2002].…”