Partial Dosage Compensation in Strepsiptera, a Sister Group of Beetles

mahajan, shivani ; bachtrog, doris;

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 hypertranscription of the single X in male Drosophila, down regulation of both X’s in XX Caenorhabditis, or in activation of one X infemale mammals. In the flour beetle Tribolium, the X appears hyper expressed in both sexes, which might represent the first of two steps to evolved osage compensation along the paths mammals may have taken (i.e.,upregulation 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 X enosvesparumbased ongenomicanalysis 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 sexlinked in X. vesparum. We use RNA-seq (RNA sequencing) toshow that dosage compensation along the X of X. vesparum is partial and heterogeneous. In particular, genes that are X- linked in both beetles and Strepsiptera appearfully dosage compensated probably through downregulation in both sexes, whereas genes on the more recently added X segment have evolved only partial dosage compensation. In addition, reanalys is 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 sexdetermination systems and even within species