Xenos vesparum Transcriptome or Gene expression and genomic data

Sex chromosomes have evolved independently in many different taxa, and so have mechanisms to compensate for expression differences on sex chromosomes in males and females. Different clades have evolved vastly different ways to achieve dosage compensation, including hyper-transcription of the single X in male Drosophila, down-regulation of both X s in XX Caenorhabditis, or inactivation of one X in female mammals. In the flour beetle Tribolium, the X appears hyper-expressed in both sexes, which might represent the first of two steps to evolve dosage compensation along the paths mammals may have taken (i.e. up-regulation of X in both sexes, followed by inactivation of one X in females). Here we test for dosage compensation in Strepsiptera, a sister taxon to beetles. We identify sex-linked chromosomes in Xenos2 vesparum2based on genomic analysis of males and females, and show that its sex chromosome consists of two chromosomal arms in Tribolium: the X chromosome that is shared between Tribolium and Strepsiptera, and another chromosome that is autosomal in Tribolium and another distantly related Strepsiptera species, but sex-linked in X.2vesparum. We use RNA-seq to show that dosage compensation along the X of X.2vesparum is partial and heterogeneous. In particular, genes that are X-linked in both beetles and Strepsiptera appear fully dosage compensated probably through down-regulation in both sexes, while genes on the more recently added X segment have evolved only partial dosage compensation. In addition, reanalysis of published RNA-seq data suggests that Tribolium has evolved dosage compensation, without hypertranscribing the X in females. Our results demonstrate that patterns of dosage compensation are highly variable across sex-determination systems and even within species.