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Ratites (1 Viewer)

Peter Kovalik

Well-known member
Zong-Ji Wang, Guang-Ji Chen, Guo-Jie Zhang, Qi Zhou. Dynamic evolution of transposable elements, demographic history, and gene content of paleognathous birds. Zoological Research, 2021, 42(1): 51-61. doi: 10.24272/j.issn.2095-8137.2020.175


Palaeognathae includes ratite and tinamou species that are important for understanding early avian evolution. Here, we analyzed the whole-genome sequences of 15 paleognathous species to infer their demographic histories, which are presently unknown. We found that most species showed a reduction of population size since the beginning of the last glacial period, except for those species distributed in Australasia and in the far south of South America. Different degrees of contraction and expansion of transposable elements (TE) have shaped the paleognathous genome architecture, with a higher transposon removal rate in tinamous than in ratites. One repeat family, AviRTE, likely underwent horizontal transfer from tropical parasites to the ancestor of little and undulated tinamous about 30 million years ago. Our analysis of gene families identified rapid turnover of immune and reproduction-related genes but found no evidence of gene family changes underlying the convergent evolution of flightlessness among ratites. We also found that mitochondrial genes have experienced a faster evolutionary rate in tinamous than in ratites, with the former also showing more degenerated W chromosomes. This result can be explained by the Hill-Robertson interference affecting genetically linked W chromosomes and mitochondria. Overall, we reconstructed the evolutionary history of the Palaeognathae populations, genes, and TEs. Our findings of co-evolution between mitochondria and W chromosomes highlight the key difference in genome evolution between species with ZW sex chromosomes and those with XY sex chromosomes.


Well-known member
Wang, Z., J. Zhang, X. Xu, C. Witt, Y. Deng, G. Chenc, G. Meng, S. Feng, L. Xu, T. Szekely, G. Zhang, and Q. Zhou (2021)
Phylogeny and sex chromosome evolution of Palaeognathae
Journal of Genetics and Genomics (advance online publication)
doi: 10.1016/j.jgg.2021.06.013

Many paleognaths (ratites and tinamous) have a pair of homomorphic ZW sex chromosomes in contrast to the highly differentiated sex chromosomes of most other birds. To understand the evolutionary causes for different tempo of sex chromosome evolution, we produced female genomes of 12 paleognathous species and reconstructed the phylogeny and the evolutionary history of paleognathous sex chromosomes. We uncovered that Palaeognathae sex chromosomes had undergone stepwise recombination suppression and formed a pattern of ‘evolutionary strata’. Nine of the 15 studied species’ sex chromosomes have maintained homologous recombination in their long pseudoautosomal regions extending over half of the entire chromosome length. We found that in older strata, the W-chromosome suffered more serious functional gene loss. Their homologous Z-linked regions, compared to other genomic regions, have produced an excess of species-specific autosomal duplicated genes that evolved female-specific expression, in contrast to their broadly-expressed progenitors. We speculate the ‘de-feminization’ of Z chromosome with underrepresentation of female-biased genes and slow divergence of sex chromosomes of paleognaths might be related to their distinctive mode of sexual selection targeting females that evolved in their common ancestors.

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