A novel neo-sex chromosome in Sylvietta brachyura (Macrosphenidae) adds to the extraordinary avian sex chromosome diversity among Sylvioidea songbirds

We report the discovery of a novel neo-sex chromosome in an African
warbler, Sylvietta brachyura (northern crombec; Macrosphenidae). This
species is part of the Sylvioidea superfamily, where four separate
autosome–sex chromosome translocation events have previously been
discovered via comparative genomics of 11 of the 22 families in this
clade. Our discovery here resulted from analyses of genomic data of
single-species representatives from three additional Sylvioidea families
(Macrosphenidae, Pycnonotidae, and Leiothrichidae). In all three species,
we confirmed the translocation of a part of chromosome 4A to the sex
chromosomes, which originated basally in Sylvioidea. In S. brachyura, we
found that a part of chromosome 8 has been translocated to the sex
chromosomes, forming a unique neo-sex chromosome in this lineage.
Furthermore, the non-recombining part of 4A in S. brachyura is smaller
than in other Sylvioidea species which suggests that recombination
continued along this region after the fusion event in the Sylvioidea
ancestor. These findings reveal additional sex chromosome diversity among
the Sylvioidea, where five separate translocation events are now
confirmed.