Centromeric satellite expansion drives genome evolution in the snowy owl

Comparative genomic studies in birds have revealed that bird genomes are relatively repeat-poor and stable in terms of karyotype, size, and gene synteny/collinearity compared to other vertebrates. One notable exception is the owls, with cytogenetic studies demonstrating large variations in karyotypes and the evolution of unusual centromeric satellite repeats in some species. However, there has so far not been an investigation into genome architecture and repeat landscape of owls.

Here, we present a chromosome-level genome assembly for the snowy owl (Bubo scandiacus). We find that the repeat DNA content in the relatively large snowy owl genome (1.6 Gb) is among the highest reported for any bird genome to date (28.34% compared to an average of ~ 10% in other birds). The bulk of the snowy owl genomic repeat landscape consists of extensive centromeric satellite arrays that form large contiguous blocks across multiple chromosomes. These arrays represent one of the largest centromeric satellite expansions reported in birds and are consistent with rapid turnover and amplification of centromeric repeats. Using gene collinearity analyses we show that the position of the centromeres are not homologous with chicken centromeres, and are located in regions with collinearity breaks to other bird genomes due to chromosomal rearrangements.

Our results support rapid satellite turnover at lineage-specific centromeres, which could have played a role in centromeric drive, reproductive isolation and speciation of the snowy owl. The extensive centromeric satellite arrays uncovered in this genome highlight centromere evolution as a potentially important driver of genome evolution in owls.