Unique sex chromosome translocations and evolutionary strata in two Sylvioidea songbird families

Avian genomes are typically stable, yet instances of chromosome fissions, fusions and translocations are known across various lineages. For example, multiple sex chromosome translocations have been described in the superfamily Sylvioidea. In this study, we examine the sex chromosomes in two Sylvioidea families, Nicatoridae and Cisticolidae, using whole-genome data. We found sex-linkage of chromosomes Z and 4A, consistent with findings in other Sylvioidea species. We also identify sex-linkage of parts of chromosome 4, marking a novel discovery for Nicatoridae and a previously documented feature in Cisticolidae. These families are non-sister taxa, and the size of the translocated region of chromosome 4 differs between them, supporting independent translocation events. We uncover variation in recombination suppression and evolutionary strata on chromosome 4 between families, as well as between two genera within Cisticolidae. This study reveals both recurrent and independent trajectories in sex chromosome evolution, deepening our understanding of complex genomes.