Chromosomal Analysis in Crotophaga ani (Aves, Cuculiformes) Reveals Extensive Genomic Reorganization and an Unusual Z-Autosome Robertsonian Translocation

Abstract

Although cytogenetics studies in cuckoos (Aves, Cuculiformes) have demonstrated an interesting karyotype variation, such as variations in the chromosome morphology and diploid number, their chromosome organization and evolution, and relation with other birds are poorly understood. Hence, we combined conventional and molecular cytogenetic approaches to investigate chromosome homologies between chicken and the smooth-billed ani (Crotophaga ani). Our results demonstrate extensive chromosome reorganization in C. ani, with interchromosomal rearrangements involving macro and microchromosomes. Intrachromosomal rearrangements were observed in some macrochromosomes, including the Z chromosome. The most evolutionary notable finding was a Robertsonian translocation between the microchromosome 17 and the Z chromosome, a rare event in birds. Additionally, the simple short repeats (SSRs) tested here were preferentially accumulated in the microchromosomes and in the Z and W chromosomes, showing no relationship with the constitutive heterochromatin regions, except in the W chromosome. Taken together, our results suggest that the avian sex chromosome is more complex than previously postulated and revealed the role of microchromosomes in the avian sex chromosome evolution, especially cuckoos.

Karyotype Evolution and Genomic Organization of Repetitive DNAs in the Saffron Finch, Sicalis flaveola (Passeriformes, Aves)

“…A distinct pattern of SSRs hybridization has been described in the sex chromosomes among birds. In general, SSRs accumulate in the W chromosomes [28,[36][37][38][39], except for Piciformes, in which no specific hybridization signal was observed in this chromosome [35,61]. The Piciformes, in contrast, showed extensive SSRs hybridization signals in the Z chromosome of all species tested so far, which were proposed as the main cause of its enlargement [35,61].…”

“…Interchromosomal rearrangements involving these small elements are rare in birds but have been found only extensively in Falconiformes and Psittaciformes [22,[24][25][26][27]. In addition, microchromosome fusions have been found in Cuculiformes, Suliformes, and Caprimulgiformes species [28,29], and future studies are necessary to investigate if it is a species-specific feature or if it is shared with other members of these orders. Future studies are also necessary for other Passeriformes members, considering the great diversity in the number of species.…”

Measurement of Chromosomal Arms and FISH Reveal Complex Genome Architecture and Standardized Karyotype of Model Fish, Genus Carassius

“…Knowledge of the karyotype is necessary in (cyto)genetics, or related fields, in order to study chromosomal rearrangements and abnormalities [5,6], the identification of sex chromosomes [7,8], and/or chromosome-specific genes [9]. Although chromosomal changes, (i.e., chromosomal losses, duplications, rearrangements), are strictly linked to a certain locus, without the knowledge of detailed karyotype, it is not possible to precisely identify chromosomal aberration, mutation or syndrome [10,11].…”

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

“…Although macrochromosomes represent approximately 77% of the average avian genome size, microchromosomes contain around 50% of the avian genes [20][21][22]. Despite the importance of microchromosomes, their organization was studied in few avian orders, and interchromosomal rearrangements involving them have been found only in few orders [12,[23][24][25][26]. Among the Passeriformes, only five species have been investigated: four oscine members, Taeniopygia guttata, Turdus merula, Serinus canaria, and Sicalis flaveola, and one suboscines member, Willisornis vidua [24,27,28].…”