Evolution and expression patterns of the neo-sex chromosomes of the crested ibis
Lulu Xu, Yandong Ren, Jiahong Wu, Tingting Cui, Rong Dong, Chen Huang, Zhe Feng, Zhe Feng, Peng Yang, Jiaqing Yuan, Xu Xiao, Jiao Liu, Jinhong Wang, Wu Chen, Da Mi, David M. Irwin, Yaping Yan, Luohao Xu, Xiaoping Yu, Gang Li, Xiaoping Yu, Gang Li
Abstract
Bird sex chromosomes play a unique role in sex-determination, and affect the sexual morphology and behavior of bird species. Core waterbirds, a major clade of birds, share the common characteristics of being sexually monomorphic and having lower levels of inter-sexual conflict, yet their sex chromosome evolution remains poorly understood. Here, by we analyse of a chromosome-level assembly of a female crested ibis (Nipponia nippon), a typical core waterbird. We identify neo-sex chromosomes resulting from fusion of microchromosomes with ancient sex chromosomes. These fusion events likely occurred following the divergence of Threskiornithidae and Ardeidae. The neo-W chromosome of the crested ibis exhibits the characteristics of slow degradation, which is reflected in its retention of abundant gametologous genes. Neo-W chromosome genes display an apparent ovary-biased gene expression, which is largely driven by genes that are retained on the crested ibis W chromosome but lost in other bird species. These results provide new insights into the evolutionary history and expression patterns for the sex chromosomes of bird species.