Figure - available from: Scientific Reports
This content is subject to copyright. Terms and conditions apply.
Metaphase plates of T. leucomelas TLE♂M01; TLE♀F01; T. rufiventris TRU♀F01 and TRU♂M01 highlighting the chromosomal mapping of microsatellites (B–H) and TleSat10 (A,I). Bar 10 μm.
Source publication
Do all birds' sex chromosomes follow the same canonical one-way direction of evolution? We combined cytogenetic and genomic approaches to analyze the process of the W chromosomal differentiation in two selected Passeriform species, named the Pale-breasted Thrush Turdus leucomelas and the Rufous-bellied thrush T. rufiventris. We characterized the fu...
Citations
... Accordingly, no interstitial telomeric sites (ITS) were detected in the Z chromosome (Supplementary Figure 4). This hypothesis was, in fact, highly unlikely, considering that this phenomenon is rare among birds, with only a limited number of studies documenting fusions between the Z (or W) and autosomes (Kretschmer et al. 2020;Huang et al. 2022;Souza et al. 2024;Pozzobon et al. 2025). Additionally, fusion events would also result in a decline rather than an increase in diploid numbers, which is inconsistent with the current scenario. ...
Contrasting with most bird species that present an ancestral-like karyotype (with 2n = 80), the only extant Cariamidae birds, the Red-legged (Cariama cristata) and Black-legged (Chunga burmeisteri) Seriemas, have high 2n and atypically large Z chromosomes. This study combined cytogenetic, bioinformatic, and genomic analyses to examine the distinctive characteristics of an unusual bird karyotype, with a focus on repetitive elements and sex chromosomes. Whole-genome alignments and chromosomal painting with a Z-chromosome-specific probe were also performed against the emu (a species with an ancestral-like karyotype). The satellitomes of C. cristata and C. burmeisteri were composed of only four and 6 long satDNAs, respectively. These satDNAs showed similarity with other repetitive sequences, mostly transposable elements, and were mapped in the pericentromeric regions of several chromosome pairs. CcrSat02-1104 mostly covered the Z and W sex chromosomes, besides being spread throughout additional chromosomes. Interstitial telomeric sites were not detected, even in the Z chromosome, and none of the 16 microsatellites tested showed positive signals on the C. cristata chromosomes. The genome alignments showed that the karyotype evolution that occurred in C. cristata may have involved significant chromosomal reshuffling, particularly fission. Notwithstanding certain internal inversions, the Z chromosome retained homology with that of the emu. However, repetitive sequences also accumulated on the Z chromosome, contributing to its enlargement relative to the pattern observed in ancestral avian groups.
... In this case, it is hypothesized that a Robertsonian translocation between a heterochromatic microchromosome and the ancestral W chromosome gave rise to the multiple sex chromosome system . Nonetheless, concerning W-autosome translocations, despite the distinct multiple ♂Z 1 Z 1 Z 2 Z 2 /♀Z 1 Z 2 W sex chromosome system described, recent research has uncovered the fusion of sex chromosomes and autosomes across various avian lineages that did not result in the emergence of a multiple-sex chromosome system (Kretschmer et al. 2020(Kretschmer et al. , 2021Sigeman et al. 2020Sigeman et al. , 2021Huang et al. 2022;Souza et al. 2024;Xu et al. 2024). This suggests that such rearrangements are more prevalent than previously assumed, and the evolution of avian W chromosomes is more dynamic than previously believed. ...
Our comprehension of avian karyotypes still needs to be improved, especially for Suliform birds. To enhance understanding of chromosomal evolution in this order, we conducted conventional and molecular cytogenetic analysis in five species, named Sula dactylatra, Sula leucogaster, Sula sula (Sulidae), Fregata magnificens (Fregatidae), and Nannopterum brasilianum (Phalacrocoracidae). The diploid chromosome number for S. dactylatra and S. leucogaster was established as 2n = 76 in males, and 2n = 75 in females, but S. sula displayed a karyotype of 2n = 76 chromosomes in males. The disparity in diploid chromosome numbers between male and female Sula is due to a multiple sex chromosome system of the Z1Z1Z2Z2/Z1Z2W type. We propose that the emergence of this multiple-sex chromosome system resulted from a Robertsonian translocation involving the W chromosome and the smallest microchromosome. Fregata magnificens exhibited a diploid number 76 (2n = 76), while N. brasilianum displayed a diploid number of 74 (2n = 74) in both sexes. The ribosomal cluster was located in one microchromosome pair in S. dactylatra, S. leucogaster, S. sula, and F. magnificens and in four pairs in N. brasilianum. Our findings provide evidence of a conserved multiple-sex chromosome system within the Sula genus, shedding light on the high karyotype diversity in Suliformes.
