Understanding microchromosomal organization and evolution in four representative woodpeckers (Picidae, Piciformes) through BAC-FISH analysis

The genome organization of woodpeckers has several distinctive features e.g., an uncommon accumulation of repetitive sequences, enlarged Z chromosomes, and atypical diploid numbers. Despite the large diversity of species, there is a paucity of detailed cytogenomic studies for this group and we thus aimed to rectify this. Genome organization patterns and hence evolutionary change in the microchromosome formation of four species (Colaptes campestris, Veniliornis spilogaster, Melanerpes candidus, and Picumnus nebulosus) was established through fluorescence in situ hybridization using bacterial artificial chromosomes originally derived from Gallus gallus and Taeniopygia guttata. Findings suggest that P. nebulosus (2n = 110), which was described for the first time, had the most basal karyotype among species of Picidae studied here, and probably arose as a result of fissions of avian ancestral macrochromosomes. We defined a new chromosomal number for V. spilogaster (2n = 88) and demonstrated microchromosomal rearrangements involving C. campestris plus a single, unique hitherto undescribed rearrangement in V. spilogaster. This comprised an inversion after a fusion involving the ancestral microchromosome 12 (homologous to chicken microchromosome 12). We also determined that the low diploid number of M. candidus is related to microchromosome fusions. Woodpeckers thus exhibit significantly rearranged karyotypes compared to the putative ancestral karyotype.

Evolution of bird sex chromosomes: a cytogenomic approach in Palaeognathae species

BACKGROUND

Different patterns of sex chromosome differentiation are seen in Palaeognathae birds, a lineage that includes the ratites (Struthioniformes, Rheiformes, Apterygiformes, Casuariiformes, and the sister group Tinamiformes). While some Tinamiform species have well-differentiated W chromosomes, both Z and W of all the flightless ratites are still morphologically undifferentiated. Here, we conducted a comprehensive analysis of the ZW differentiation in birds using a combination of cytogenetic, genomic, and bioinformatic approaches. The whole set of satDNAs from the emu (Dromaius novaehollandiae) was described and characterized. Furthermore, we examined the in situ locations of these satDNAs alongside several microsatellite repeats and carried out Comparative Genomic Hybridizations in two related species: the greater rhea (Rhea americana) and the tataupa tinamou (Crypturellus tataupa).

RESULTS

From the 24 satDNA families identified (which represent the greatest diversity of satDNAs ever uncovered in any bird species), only three of them were found to accumulate on the emu's sex chromosomes, with no discernible accumulation observed on the W chromosome. The W chromosomes of both the greater rhea and the emu did not exhibit a significant buildup of either C-positive heterochromatin or repetitive DNAs, indicating their large undifferentiation both at morphological and molecular levels. In contrast, the tataupa tinamou has a highly differentiated W chromosome that accumulates several DNA repeats.

CONCLUSION

The findings provide new information on the architecture of the avian genome and an inside look at the starting points of sex chromosome differentiation in birds.

Satellite DNAs, heterochromatin, and sex chromosomes of the wattled jacana (Charadriiformes; Jacanidae): a species with highly rearranged karyotype

Charadriiformes, which comprises shorebirds and their relatives, is one of the most diverse avian orders, with over 390 species showing a wide range of karyotypes. Here, we isolated and characterized the whole collection of satellite DNAs (satDNAs) at both molecular and cytogenetic levels of one of its representative species, named the wattled jacana (Jacana jacana), a species that contains a typical ZZ/ZW sex chromosome system and a highly rearranged karyotype. In addition, we also investigate the in situ location of telomeric and microsatellite repeats. A small catalog of 11 satDNAs was identified that typically accumulated on microchromosomes and on the W chromosome. The latter also showed a significant accumulation of telomeric signals, being (GA)10 the only microsatellite with positive hybridization signals among all the 16 tested ones. These current findings contribute to our understanding of the genomic organization of repetitive DNAs in a bird species with high degree of chromosomal reorganization contrary to the majority of bird species that have stable karyotypes.

Satellitome Analysis in the Southern Lapwing (Vanellus chilensis) Genome: Implications for SatDNA Evolution in Charadriiform Birds

Vanellus (Charadriidae; Charadriiformes) comprises around 20 species commonly referred to as lapwings. In this study, by integrating cytogenetic and genomic approaches, we assessed the satellite DNA (satDNA) composition of one typical species, Vanellus chilensis, with a highly conserved karyotype. We additionally underlined its role in the evolution, structure, and differentiation process of the present ZW sex chromosome system. Seven distinct satellite DNA families were identified within its genome, accumulating on the centromeres, microchromosomes, and the W chromosome. However, these identified satellite DNA families were not found in two other Charadriiformes members, namely Jacana jacana and Calidris canutus. The hybridization of microsatellite sequences revealed the presence of a few repetitive sequences in V. chilensis, with only two out of sixteen displaying positive hybridization signals. Overall, our results contribute to understanding the genomic organization and satDNA evolution in Charadriiform birds.

Understanding the chromosomal evolution in cuckoos (Aves, Cuculiformes): a journey through unusual rearrangements

The Cuculiformes are a family of over 150 species that live in a range of habitats, such as forests, savannas, and deserts. Here, bacterial artificial chromosome (BAC) probes (75 from chicken and 14 from zebra finch macrochromosomes 1-10 +ZW and for microchromosomes 11-28 (except 16)) were used to investigate chromosome homologies between chicken and the squirrel cuckoo (Piaya cayana). In addition, repetitive DNA probes were applied to characterize the chromosome organization and to explore the role of these sequences in the karyotype evolution of P. cayana. We also applied BAC probes for chicken chromosome 17 and Z to the guira cuckoo (Guira guira) to test whether this species has an unusual Robertsonian translocation between a microchromosome and the Z chromosome, recently described in the smooth-billed ani (Crotophaga ani). Our results revealed extensive chromosome reorganization with inter- and intrachromosomal rearrangements in P. cayana, including a conspicuous chromosome size and heterochromatin polymorphism on chromosome pair 20. Furthermore, we confirmed that the Z-autosome Robertsonian translocation found in C. ani is also found in G. guira, not P. cayana. These findings suggest that this translocation occurred prior to the divergence between C. ani and G. guira, but after the divergence with P. cayana.

Chromosomal Evolution of Suboscines: Karyotype Diversity and Evolutionary Trends in Ovenbirds (Passeriformes, Furnariidae)

Furnariidae (ovenbirds) is one of the most diversified families in the Passeriformes order and Suboscines suborder. Despite the great diversity of species, cytogenetic research is still in its early stages, restricting our knowledge of their karyotype evolution. We combined traditional and molecular cytogenetic analyses in three representative species, Synallaxis frontalis, Syndactyla rufosuperciliata, and Cranioleuca obsoleta, to examine the chromosomal structure and evolution of ovenbirds. Our findings revealed that all the species studied had the same diploid number (2n = 82). Differences in chromosomal morphology of some macrochromosomes indicate the presence of intrachromosomal rearrangements. Although the three species only had the 18S rDNA on one microchromosome pair, chromosomal mapping of six simple short repeats revealed a varied pattern of chromosome distribution among them, suggesting that each species underwent different repetitive DNA accumulation upon their divergence. The interspecific comparative genomic hybridization experiment revealed that the Furnariidae species investigated carry centromeric regions enriched in similar repetitive sequences, bolstering the Furnariidae family's karyotype conservation. Nonetheless, the outgroup species Turdus rufiventris (Turdidae) demonstrated an advanced stage of sequence divergence with hybridization signals that were almost entirely limited to a few microchromosomes. Overall, the findings imply that Furnariidae species have a high degree of chromosomal conservation, and we could also observe a differentiation of repetitive sequences in both Passeriformes suborders (Suboscines and Oscines).

Cytogenetic Evidence Clarifies the Phylogeny of the Family Rhynchocyclidae (Aves: Passeriformes)

The phylogenetic position and taxonomic status of Rhynchocyclidae (Aves: Passeriformes) have been the subject of debate since their first description. In most models, Rhynchocyclidae represents a subfamily-level taxon placed within the Tyrant Flycatchers (Tyrannidae). Considering that this classification does not include cytotaxonomic characters, we tested the hypothesis that the chromosome organization of Rhynchocyclidae members differs from that of Tyrannidae. Hence, we selected two species, Tolmomyias sulphurescens, and Pitangus sulphuratus, representing Rhynchocyclidae and Tyrannidae, respectively. Results revealed a diploid number (2n) of 60 in T. sulphurescens and 2n = 80 in P. sulphuratus, indicating significant chromosomal differences. Chromosome mapping of Gallus gallus (GGA) and Taeniopygia guttata bacterial artificial chromosome (BAC) corresponding to chromosomes GGA1-28 (except 16) revealed that the genome evolution of T. sulphurescens involved extensive chromosome fusions of macrochromosomes and microchromosomes. On the other hand, P. sulphuratus retained the ancestral pattern of organization of macrochromosomes (except the centric fission involving GGA1) and microchromosomes. In conclusion, comparing our results with previous studies in Tyrant Flycatchers and allies indicates that P. sulphuratus has similar karyotypes to other Tyrannidae members. However, T. sulphurescens does not resemble the Tyrannidae family, reinforcing family status to the clade named Rhynchocyclidae.

Cytotaxonomy of Gallinula melanops (Gruiformes, Rallidae): Karyotype evolution and phylogenetic inference

Although Rallidae is the most diverse family within Gruiformes, there is little information concerning the karyotype of the species in this group. In fact, Gallinula melanops, a species of Rallidae found in Brazil, is among the few species studied cytogenetically, but only with conventional staining and repetitive DNA mapping, showing 2n=80. Thus, in order to understand the karyotypic evolution and phylogeny of this group, the present study aimed to analyze the karyotype of G. melanops by classical and molecular cytogenetics, comparing the results with other species of Gruiformes. The results show that G. melanops has the same chromosome rearrangements as described in Gallinula chloropus (Clade Fulica), including fission of ancestral chromosomes 4 and 5 of Gallus gallus (GGA), beyond the fusion between two of segments resultants of the GGA4/GGA5, also fusions between the chromosomes GGA6/GGA7. Thus, despite the fact that some authors have suggested the inclusion of G. melanops in genus Porphyriops, our molecular cytogenetic results confirm its place in the Gallinula genus.

Comparative chromosome painting in hummingbirds (Trochilidae)

Hummingbirds (Trochilidae) are one of the most enigmatic avian groups, and also among the most diverse, with approximately 360 recognized species in 106 genera, of which 43 are monotypic. This fact has generated considerable interest in the evolutionary biology of the hummingbirds, which is reflected in a number of DNA-based studies. However, only a few of them explored chromosomal data. Given this, the present study provides an analysis of the karyotypes of three species of Neotropical hummingbirds, Anthracothorax nigricollis (ANI), Campylopterus largipennis (CLA), and Hylocharis chrysura (HCH), in order to analyze the chromosomal processes associated with the evolution of the Trochilidae. The diploid number of ANI is 2n=80 chromosomes, while CLA and HCH have identical karyotypes, with 2n=78. Chromosome painting with Gallus gallus probes (GGA1-12) shows that the hummingbirds have a karyotype close to the proposed ancestral bird karyotype. Despite this, an informative rearrangement was detected: an in-tandem fusion between GGA7 and GGA9 found in CLA and HCH, but absent in ANI. A comparative analysis with the tree of life of the hummingbirds indicated that this fusion must have arisen following the divergence of a number of hummingbird species.

Extensive chromosomal fissions and repetitive DNA accumulation shaped the atypical karyotypes of two Ramphastidae (Aves: Piciformes) species

In contrast to the ‘avian-like’ diploid number (2n = 80), most toucans and aracaris (Piciformes: Ramphastidae) have divergent karyotypes, exhibiting a higher 2n. To identify the chromosomal rearrangements that shaped the karyotype of these species, we applied chicken macrochromosome paints 1–10 and 11 microsatellite sequences to the chromosomes of two representative species, Pteroglossus inscriptus and Ramphastos tucannus tucannus. Paints of chicken chromosomes revealed that at least the first five ancestral chromosomes have undergone fissions, and a fusion between a segment of chicken chromosome 1 and a segment from chromosome 3 occurred in both species. The microsatellite sequences were accumulated mainly in the Z chromosome and in several microchromosomes in both species. These results suggest that the genomes of the Ramphastidae have been shaped by extensive fissions and repetitive DNA accumulation as the main driving forces leading to the higher 2n as found in these species. Furthermore, our results suggest that the putative ancestral karyotype of Ramphastidae already had a high diploid number, probably close to 2n = 112, similar to that observed in P. inscriptus and R. t. tucannus.

Chromosomal Evolution in the Phylogenetic Context: A Remarkable Karyotype Reorganization in Neotropical Parrot Myiopsitta monachus (Psittacidae)

Myiopsitta monachus is a small Neotropical parrot (Psittaciformes: Arini Tribe) from subtropical and temperate regions of South America. It has a diploid chromosome number 2n = 48, different from other members of the Arini Tribe that have usually 70 chromosomes. The species has the lowest 2n within the Arini Tribe. In this study, we combined comparative chromosome painting with probes generated from chromosomes of Gallus gallus and Leucopternis albicollis, and FISH with bacterial artificial chromosomes (BACs) selected from the genome library of G. gallus with the aim to shed light on the dynamics of genome reorganization in M. monachus in the phylogenetic context. The homology maps showed a great number of fissions in macrochromosomes, and many fusions between microchromosomes and fragments of macrochromosomes. Our phylogenetic analysis by Maximum Parsimony agree with molecular data, placing M. monachus in a basal position within the Arini Tribe, together with Amazona aestiva (short tailed species). In M. monachus many chromosome rearrangements were found to represent autopomorphic characters, indicating that after this species split as an independent branch, an intensive karyotype reorganization took place. In addition, our results show that M. monachus probes generated by flow cytometry provide novel cytogenetic tools for the detection of avian chromosome rearrangements, since this species presents breakpoints that have not been described in other species.

The distribution of 45S rDNA sites in bird chromosomes suggests multiple evolutionary histories

The distribution of 45S rDNA cluster in avian karyotypes varies in different aspects, such as position, number of bearer chromosomes, and bearers being macro- or microchromosomes. The present study investigated the patterns of variation in the 45S rDNA-bearer chromosomes of birds in order to understand the evolutionary dynamics of the cluster configuration and its contribution to the evolution of bird karyotypes. A total of 73 bird species were analyzed, including both published data and species for which rDNA-FISH was conducted for the first time. In most birds, the 45S rDNA clusters were located in a single pair of microchromosomes. Hence, the location of 45S rDNA in macrochromosomes, observed only in Neognathae species, seems to be a derived state, probably the result of chromosomal fusion between microchromosomes and distinct macrochromosomes. Additionally, the 45S rDNA was observed in multiple microchromosomes in different branches of the bird phylogeny, suggesting recurrence of dispersion processeses, such as duplications and translocations. Overall, this study indicated that the redistribution of the 45S rDNA sites in bird chromosomes followed different evolutionary trajectories with respect to each lineage of the class Aves.

Comparative analyses of three swallow species (Aves, Passeriformes, Hirundinidae): Insights on karyotype evolution and genomic organization

Despite the richness of species in the Hirudinidae family, little is known about the genome organization of swallows. The Progne tapera species presents genetic and morphological difference when compared to other members of the same genus. Hence, the aims of this study were to analyze the chromosomal evolution of three species Progne tapera, Progne chalybea and Pygochelidon cyanoleuca - by comparative chromosome painting using two sets of probes, Gallus gallus and Zenaida auriculata, in order to determine chromosome homologies and the relationship between these species. All karyotypes exhibited 76 chromosomes with similar morphology, except for the 5th, 6th and 7th chromosome pairs in P. cyanoleuca. Additionally, comparative chromosome painting demonstrated the same hybridization pattern in the two Progne, which was similar to the putative avian ancestral karyotype, except for the centric fission in the first pair, as found in other Passeriformes. Thus, these data display a close relationship between the Progne species. Although P. cyanoleuca demonstrated the same fission in the first pair of the ancestral syntenic (GGA1), it also showed an additional chromosomal rearrangement for this species, namely a fusion with a microchromosome in the seventh pair.

Novel insights into chromosome evolution of Charadriiformes: extensive genomic reshuffling in the wattled jacana (Jacana jacana, Charadriiformes, Jacanidae)

The order Charadriiformes comprises three major clades: Lari and Scolopaci as sister group to Charadrii. Until now, only three Charadriiformes species have been studied by chromosome painting: Larus argentatus (Lari), Burhinus oedicnemus and Vanellus chilensis (Charadrii). Hence, there is a lack of information concerning the third clade, Scolapaci. Based on this, and to gain a better understanding of karyotype evolution in the order Charadriiformes, we applied conventional and molecular cytogenetic approaches in a species belonging to clade Scolopaci - the wattled jacana (Jacana jacana) - using Gallus gallus and Zenaida auriculata chromosome-specific probes. Cross-species evaluation of J. jacana chromosomes shows extensive genomic reshuffling within macrochromosomes during evolution, with multiple fission and fusion events, although the diploid number remains at high level (2n=82). Interestingly, this species does not have the GGA7-8 fusion, which was found in two representatives of Charadrii clade, reinforcing the idea that this fusion may be exclusive to the Charadrii clade. In addition, it is shown that the chromosome evolution in Charadriiformes is complex and resulted in species with typical and atypical karyotypes. The karyotypic features of Scolopaci are very different from those of Charadrii and Lari, indicating that after divergence, each suborder has undergone different chromosome rearrangements.

Evolution of Bird Sex Chromosomes Narrated by Repetitive Sequences: Unusual W Chromosome Enlargement in Gallinula melanops (Aves: Gruiformes: Rallidae)

Among birds, species with the ZZ/ZW sex determination system generally show significant differences in morphology and size between the Z and W chromosomes (with the W usually being smaller than the Z). In the present study, we report for the first time the karyotype of the spot-flanked gallinule (Gallinula melanops) by means of classical and molecular cytogenetics. The spot-flanked gallinule has 2n = 80 (11 pairs of macrochromosomes and 29 pairs of microchromosomes) with an unusual W chromosome that is larger than the Z. Besides being totally heterochromatic, it has a secondary constriction in its long arm corresponding to the nucleolar organizer region, as confirmed by both silver staining and mapping of 18S rDNA probes. This is an unprecedented fact among birds. Additionally, 18S rDNA sites were also observed in 6 microchromosomes, while 5S rDNA was found in just 1 microchromosomal pair. Seven out of the 11 used microsatellite sequences were found to be accumulated in microchromosomes, and 6 microsatellite sequences were found in the W chromosome. In addition to the involvement of heterochromatin and repetitive DNAs in the differentiation of the large W chromosome, the results also show an alternative scenario that highlights the plasticity that shapes the evolutionary history of bird sex chromosomes.

Polymorphism of Sooty-fronted Spinetail (Synallaxis frontalis Aves: Furnariidae): Evidence of chromosomal rearrangements by pericentric inversion in autosomal macrochromosomes

The Passeriformes is the most diverse and cytogenetically well-known clade of birds, comprising approximately 5,000 species. The sooty-fronted spinetail (Synallaxis frontalis Aves: Furnariidae) species, which belongs to the order Passeriformes, is typically found in South America, where it is widely distributed. Polymorphisms provide genetic variability, important for several evolutionary processes, including speciation and adaptation to the environment. The aim of this work was to analyze the possible cytotypes and systemic events involved in the species polymorphism. Of the sampled 19 individuals, two thirds were polymorphic, an event supposedly linked to mutations resulting from genomic evolution that can be transmitted hereditarily. A chromosomal polymorphism was detected between the 1st and 3rdpairs of autosomal macrochromosomes. This type of polymorphism is related to a pericentric inversion in regions involving chromosomal rearrangements. Differently from other polymorphism studies that report a link between polymorphic chromosomes and phenotypic changes, S. frontalis did not present any morphological variation in the sampled individuals.

Distribution of CR1-like transposable element in woodpeckers (Aves Piciformes): Z sex chromosomes can act as a refuge for transposable elements

Birds have relatively few repetitive sequences compared to other groups of vertebrates; however, the members of order Piciformes (woodpeckers) have more of these sequences, composed mainly of transposable elements (TE). The TE most often found in birds is a retrotransposon chicken repeat 1 (CR1). Piciformes lineages were subjected to an expansion of the CR1 elements, carrying a larger fraction of transposable elements. This study compared patterns of chromosome distribution among five bird species, through chromosome mapping of the CR1 sequence and reconstructed their phylogenetic tree. We analyzed several members of Piciformes (Colaptes campestris, Colaptes melanochloros, Melanerpes candidus, and Veniliornis spilogaster), as well as Galliformes (Gallus gallus). Gallus gallus is the species with which most genomic and hence cytogenetic studies have been performed. The results showed that CR1 sequences are a monophyletic group and do not depend on their hosts. All species analyzed showed a hybridization signal by fluorescence in situ hybridization (FISH). In all species, the chromosomal distribution of CR1 was not restricted to heterochromatin regions in the macrochromosomes, principally pair 1 and the Z sex chromosome. Accumulation in the Z sex chromosomes can serve as a refuge for transposable elements. These results highlight the importance of transposable elements in host genomes and karyotype evolution.

Chromosomal polymorphism and comparative chromosome painting in the rufous-collared sparrow (Zonotrichia capensis)

Zonotrichia capensis is widely distributed in the Neotropics. Previous cytogenetic studies demonstrated the presence of polymorphisms in two chromosome pairs (ZCA2 and ZCA4). Here, we report results based on comparative chromosome painting, using probes derived from Gallus gallus and Leucopternis albicollis, focused on characterizing the chromosome organization of Z. capensis. Our results demonstrate the conservation of ancestral syntenies as observed previously in other species of passerine. Syntenies were rearranged by a series of inversions in the second chromosome as described in other Passeriformes, but in this species, by using probes derived from L. albicollis we observed an extra inversion in the second chromosome that had not previously been reported. We also report a paracentric inversion in pair 3; this chromosome corresponds to the second chromosome in Zonotrichia albicollis and may indicate the presence of ancestral inversions in the genus. The chromosomal inversions we found might be important for understanding the phenotypic variation that exists throughout the distribution of Z. capensis.

Multidirectional chromosome painting in Synallaxis frontalis (Passeriformes, Furnariidae) reveals high chromosomal reorganization, involving fissions and inversions

In this work we performed comparative chromosome painting using probes from Gallus gallus (GGA) Linnaeus, 1758 and Leucopternis albicollis (LAL) Latham, 1790 in Synallaxis frontalis Pelzeln, 1859 (Passeriformes, Furnariidae), an exclusively Neotropical species, in order to analyze whether the complex pattern of intrachromosomal rearrangements (paracentric and pericentric inversions) proposed for Oscines and Suboscines is shared with more basal species. S. frontalis has 82 chromosomes, similar to most Avian species, with a large number of microchromosomes and a few pairs of macrochromosomes. We found polymorphisms in pairs 1 and 3, where homologues were submetacentric and acrocentric. Hybridization of GGA probes showed syntenies in the majority of ancestral macrochromosomes, except for GGA1 and GGA2, which hybridized to more than one pair of chromosomes each. LAL probes confirmed the occurrence of intrachromosomal rearrangements in the chromosomes corresponding to GGA1q, as previously proposed for species from the order Passeriformes. In addition, LAL probes suggest that pericentric inversions or centromere repositioning were responsible for variations in the morphology of the heteromorphic pairs 1 and 3. Altogether, the analysis of our data on chromosome painting and the data published in other Passeriformes highlights chromosomal changes that have occurred during the evolution of Passeriformes.

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

An extensive karyotype variation is found among species belonging to the Columbidae family of birds (Columbiformes), both in diploid number and chromosomal morphology. Although clusters of repetitive DNA sequences play an important role in chromosomal instability, and therefore in chromosomal rearrangements, little is known about their distribution and amount in avian genomes. The aim of this study was to analyze the distribution of 11 distinct microsatellite sequences, as well as clusters of 18S rDNA, in nine different Columbidae species, correlating their distribution with the occurrence of chromosomal rearrangements. We found 2n values ranging from 76 to 86 and nine out of 11 microsatellite sequences showed distinct hybridization signals among the analyzed species. The accumulation of microsatellite repeats was found preferentially in the centromeric region of macro and microchromosomes, and in the W chromosome. Additionally, pair 2 showed the accumulation of several microsatellites in different combinations and locations in the distinct species, suggesting the occurrence of intrachromosomal rearrangements, as well as a possible fission of this pair in Geotrygon species. Therefore, although birds have a smaller amount of repetitive sequences when compared to other Tetrapoda, these seem to play an important role in the karyotype evolution of these species.

Organização genômica do RNA repetitivo e evolução do cariótipo em Elaenia flavogaster (Passeriformes, Aves)

Pouco se sabe sobre a organização de sequências repetitivas no cariótipo das Aves, e sondas de microssatélites foram usadas em um pequeno grupo de espécies até o momento. Tyrannidae (Passeriformes, Suboscines), é uma das maiores famílias de aves das Américas, e dados citogenéticos evidenciaram uma interessante variação cariotípica nesse grupo. Assim, o objetivo desse estudo foi analisar o cariótipo da guaracava-de-barriga-amarela (Elaenia flavogaster), por meio de técnicas de citogenética clássica (coloração convencional com Giemsa e bandeamento C) e molecular (sondas teloméricas, 18S rDNA e sondas de microssatélites: (CAT)10, (GAG)10, (GC)15, (GA)15 e (TA)15). Os resultados mostraram um número diploide de 2n=80. A distribuição da heterocromatina exibiu marcações apenas nos centrômeros dos cromossomos. O padrão de hibridização das sondas teloméricas revelou sinais mais intensos nos microcromossomos e ausência de sequências teloméricas intersticiais (ITSs), reforçando o fato de que ITSs são menos frequentes em ordens de Aves consideradas mais derivadas, visto que em Ratitas e Galloanserae essas sequências já foram detectadas. As sondas de 18S rDNA marcaram dois pares de microcromossomos, semelhante a Elaenia spectabilis e Serpophaga subcristata, indicando que esta característica pode representar uma sinapomorfia dentro de Elaeniinae, pois até o momento não foi encontrada em outras subfamílias dentro de  Tyrannidae. Das sondas de microssatélites utilizadas, (GA)15 e (TA)15 não produziram sinais detectáveis, já as sondas de microssatélites (CAT)10 marcaram apenas na extremidade distal do braço longo do 1º par, e em alguns microcromossomos, as sondas (GAG)10 apresentaram intensa marcação nos microcromossomos, diferentemente de Leptotila verreauxi (Columbiformes), na qual essas sondas marcam poucos microcromossomos. Já as sondas (GC)15 marcaram apenas o braço curto de um microcromossomo e o braço longo de um macrocromossomo. Esses resultados evidenciam a variação de distribuição dessas sequências repetitivas em diferentes grupos de Aves e o pequeno número de sinais detectados concorda com o fato de que o genoma das Aves é compacto com pouca quantidade de DNA repetitivo. Conclui-se que a evolução do cariótipo dos tiranídeos envolveu a amplificação de sítios de 18S rDNA e que apresenta uma distribuição distinta de microssatélites quando comparada com espécies de outras ordens.

Chromosome Painting in Trogon s. surrucura (Aves, Trogoniformes) Reveals a Karyotype Derived by Chromosomal Fissions, Fusions, and Inversions

Trogons are forest birds with a wide distribution, being found in Africa, Asia, and America, and are included in the order Trogoniformes, family Trogonidae. Phylogenetic studies using molecular data have not been able to determine the phylogenetic relationship among the different genera of trogons. So far, no cytogenetic data for these birds exist. Hence, the aim of this study was to characterize the karyotype of Trogon surrucura surrucura by means of classical and molecular cytogenetics. We found a diploid chromosome number of 2n = 82, similar to most birds, with several derived features compared to chicken and the putative ancestral avian karyotype. T. s. surrucura showed 3 pairs of microchromosomes bearing 18S rDNA clusters. The Z and W sex chromosomes were of similar size but could readily be identified by morphological differences. Using chromosome painting with whole chromosome probes from Gallus gallus and Leucopternis albicollis, we found that the chromosomes homologous to chicken chromosomes 2 and 5 correspond to 2 different pairs in T. s. surrucura and L. albicollis, due to the occurrence of centric fissions. Paracentric inversions were detected in the segment homologous to chicken chromosome 1q, and we confirmed the recurrence of breakpoints when our results were compared to other species of birds already analyzed by FISH or by in silico genome assembly.

Multiple sex chromosome system in penguins (Pygoscelis, Spheniscidae)

Penguins are classified in the order Sphenisciformes into a single family, Spheniscidae. The genus Pygoscelis Wagler, 1832, is composed of three species, Pygoscelis antarcticus Forster, 1781, P. papua Forster, 1781 and P. adeliae Hombron & Jacquinot, 1841. In this work, the objective was to describe and to compare the karyotypes of Pygoscelis penguins contributing genetic information to Sphenisciformes. The metaphases were obtained by lymphocyte culture, and the diploid number and the C-banding pattern were determined. P. antarcticus has 2n = 92, P. papua 2n = 94 and P. adeliae exhibited 2n = 96 in males and 2n = 95 in females. The difference of diploid number in P. adeliae was identified as a multiple sex chromosome system where males have Z1Z1Z2Z2 and females Z1Z2W. The C-banding showed the presence of a heterochromatic block in the long arm of W chromosome and Z2 was almost entirely heterochromatic. The probable origin of a multiple system in P. adeliae was a translocation involving the W chromosome and the chromosome ancestral to Z2. The comparison made possible the identification of a high karyotype homology in Sphenisciformes which can be seen in the conservation of macrochromosomes and in the Z chromosome. The karyotypic divergences in Pygoscelis are restricted to the number of microchromosomes and W, which proved to be highly variable in size and morphology. The data presented in this work corroborate molecular phylogenetic proposals, supporting the monophyletic origin of penguins and intraspecific relations.

Intrachromosomal rearrangements in two representatives of the genus Saltator (Thraupidae, Passeriformes) and the occurrence of heteromorphic Z chromosomes

Saltator is a genus within family Thraupidae, the second largest family of Passeriformes, with more than 370 species found exclusively in the New World. Despite this, only a few species have had their karyotypes analyzed, most of them only with conventional staining. The diploid number is close to 80, and chromosome morphology is similar to the usual avian karyotype. Recent studies using cross-species chromosome painting have shown that, although the chromosomal morphology and number are similar to many species of birds, Passeriformes exhibit a complex pattern of paracentric and pericentric inversions in the chromosome homologous to GGA1q in two different suborders, Oscines and Suboscines. Hence, considering the importance and species richness of Thraupidae, this study aims to analyze two species of genus Saltator, the golden-billed saltator (S. aurantiirostris) and the green-winged saltator (S. similis) by means of classical cytogenetics and cross-species chromosome painting using Gallus gallus and Leucopternis albicollis probes, and also 5S and 18S rDNA and telomeric sequences. The results show that the karyotypes of these species are similar to other species of Passeriformes. Interestingly, the Z chromosome appears heteromorphic in S. similis, varying in morphology from acrocentric to metacentric. 5S and 18S probes hybridize to one pair of microchromosomes each, and telomeric sequences produce signals only in the terminal regions of chromosomes. FISH results are very similar to the Passeriformes already analyzed by means of molecular cytogenetics (Turdus species and Elaenia spectabilis). However, the paracentric and pericentric inversions observed in Saltator are different from those detected in these species, an observation that helps to explain the probable sequence of rearrangements. As these rearrangements are found in both suborders of Passeriformes (Oscines and Suboscines), we propose that the fission of GGA1 and inversions in GGA1q have occurred very early after the radiation of this order.

Karyotypic evolution of ribosomal sites in buffalo subspecies and their crossbreed

Domestic buffaloes are divided into two group based on cytogenetic characteristics and habitats: the “river buffaloes” with 2n = 50 and the “swamp buffaloes”, 2n = 48. Nevertheless, their hybrids are viable, fertile and identified by a 2n = 49. In order to have a better characterization of these different cytotypes of buffaloes, and considering that NOR-bearing chromosomes are involved in the rearrangements responsible for the karyotypic differences, we applied silver staining (Ag-NOR) and performed fluorescent in situ hybridization (FISH) experiments using 18S rDNA as probe. Metaphases were obtained through blood lymphocyte culture of 21 individuals, including river, swamp and hybrid cytotypes. Ag-NOR staining revealed active NORs on six chromosome pairs (3p, 4p, 6, 21, 23, 24) in the river buffaloes, whereas the swamp buffaloes presented only five NOR-bearing pairs (4p, 6, 20, 22, 23). The F1 cross-breed had 11 chromosomes with active NORs, indicating expression of both parental chromosomes. FISH analysis confirmed the numerical divergence identified with Ag-NOR. This result is explained by the loss of the NOR located on chromosome 4p in the river buffalo, which is involved in the tandem fusion with chromosome 9 in this subspecies. A comparison with the ancestral cattle karyotype suggests that the NOR found on the 3p of the river buffalo may have originated from a duplication of ribosomal genes, resulting in the formation of new NOR sites in this subspecies.

Molecular cytogenetic characterization of multiple intrachromosomal rearrangements in two representatives of the genus Turdus (Turdidae, Passeriformes)

Turdus rufiventris and Turdus albicollis, two songbirds belonging to the family Turdidae (Aves, Passeriformes) were studied by C-banding, 18S rDNA, as well as the use of whole chromosome probes derived from Gallus gallus (GGA) and Leucopternis albicollis (LAL). They showed very similar karyotypes, with 2n = 78 and the same pattern of distribution of heterochromatic blocks and hybridization patterns. However, the analysis of 18/28S rDNA has shown differences in the number of NOR-bearing chromosomes and ribosomal clusters. The hybridization pattern of GGA macrochromosomes was similar to the one found in songbirds studied by Fluorescent in situ hybridization, with fission of GGA 1 and GGA 4 chromosomes. In contrast, LAL chromosome paintings revealed a complex pattern of intrachromosomal rearrangements (paracentric and pericentric inversions) on chromosome 2, which corresponds to GGA1q. The first inversion changed the chromosomal morphology and the second and third inversions changed the order of chromosome segments. Karyotype analysis in Turdus revealed that this genus has derived characteristics in relation to the putative avian ancestral karyotype, highlighting the importance of using new tools for analysis of chromosomal evolution in birds, such as the probes derived from L. albicollis, which make it possible to identify intrachromosomal rearrangements not visible with the use of GGA chromosome painting solely.

NOR- bearing as a plesiomorphic characteristic in Mimus saturninus (Passeriformes Mimidae)

The order Passeriformes is the largest group of species karyotyped among birds, however little is known about the cytogenetic of the Mimidae family, registering only karyology basic data (giemsa staining). The aim of this study was to analyze the chromosomal complement from the species Mimus saturninus by conventional staining and differential chromosome banding. Diploid number and chromosome morphology were determined, as well as the distribution pattern of constitutive heterochromatin (CBG-banding), GTG-banding andAgNOR staining (NORs). The Chalk-browed Mockingbird has 2n=80. The first and fourth pairs are submetacentric and the second, third and fifth are acrocentric. The remaining chromosomes pairs of the complement have telocentric morphology. The Z chromosome is submetacentric and the W is metacentric. CBG-banding showed positive staining in the pericentromeric region of most macrochromosomes and microchromosomes and also at Z chromosome, differently from W chromosome which appeared totally heterochromatic. The GTG-banding was similar to Gallus gallus and in other species which have already been GTG-banded. The NORs were identified in a pair of microchromosomes characterized by presenting a remarkable secondary constriction. This can be considered as a plesiomorphic characteristic for M. saturninus once baseline groups (Paleognathae) also showed a pair of microchromosomes bearing NORs.

Cytogenetic comparison of Podocnemis expansa and Podocnemis unifilis: A case of inversion and duplication involving constitutive heterochromatin

Podocnemis expansa and P. unifilis present 2n = 28 chromosomes, a diploid number similar to those observed in other species of the genus. The aim of this study was to characterize these two species using conventional staining and differential CBG-, GTG and Ag-NOR banding. We analyzed specimens of P. expansa and P. unifilis from the state of Tocantins (Brazil), in which we found a 2n = 28 and karyotypes differing in the morphology of the 13(th) pair, which was submetacentric in P. expansa and telocentric in P. unifilis. The CBG-banding patterns revealed a heterochromatic block in the short arm of pair 13 of P. expansa and an interstitial one in pair 13 of P. unifilis, suggesting a pericentric inversion. Pair 14 of P. unifilis showed an insterstitial band in the long arm that was absent in P. expansa, suggesting a duplication in this region. Ag-NORs were observed in the first chromosome pair of both species and was associated to a secondary constriction and heterochromatic blocks.

Nucleolar organizer regions in Sittasomus griseicapillus and Lepidocolaptes angustirostris (Aves, Dendrocolaptidae): Evidence of a chromosome inversion

Cytogenetic studies in birds are still scarce compared to other vertebrates. Woodcreepers (Dendrocolaptidae) are part of a highly specialized group within the Suboscines of the New World. They are forest birds exclusive to the Neotropical region and similar to woodpeckers, at a comparable evolutionary stage. This paper describes for the first time the karyotypes of the Olivaceous and the Narrow-billed Woodcreeper using conventional staining with Giemsa and silver nitrate staining of the nucleolar organizer regions (Ag-NORs). Metaphases were obtained by fibular bone marrow culture. The chromosome number of the Olivaceous Woodcreeper was 2n = 82 and of the Narrow-billed Woodcreeper, 2n = 82. Ag-NORs in the largest macrochromosome pair and evidence of a chromosome inversion are described herein for the first time for this group.