Sexual differences in the gonochoristic tardigrade Paramacrobiotus metropolitanus,

Sex dimorphism is a diversification that can be observed in single species of gonochoristic animals. Phylum Tardigrada exhibits remarkable diversity in sex dimorphism in its morphology and behavior. Despite the wealth of genomic and zoological knowledge accumulating, sexual genetic differences of tardigrades have been identified yet. In this study, we focused on the gonochoristic species Paramacrobiotus metropolitanus, employing omics analyses to unravel the basis of sex differences. Approximately 2,000 male-biased expression genes were concentrated in 29 non-male-specific genomic loci, of which two paralogs of a new Doublesex-Mab-3-related (DM) subfamily specific to Macrobiotidae were discovered. We also identified several tardigrade specific anhydrobiosis genes exhibiting sex-biased expression, suggesting a potential role in protecting sex-specific gametes. The existence of male-biased, but not male specific genomic loci and the limited conservation of the newly identified dimorphically-expressed DM subfamily would provide the foundation for understanding the diverse sex determination cascade in tardigrades. Overall design: RNA-Seq of adult males and females