Sponge genomes reveal a pre-metazoan origin of the sex determination toolkit and sex chromosomes
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Sex has profoundly shaped animal biology and evolution, yet sex determination is strikingly diverse and its evolutionary origins remain poorly understood outside bilaterians. We investigate the molecular basis of sex determination in eight gonochoristic sponge species using integrated genomic and transcriptomic analyses. We identify sex chromosomes in two species, likely arising through chromosomal rearrangements, and find widespread polygenic sex determination across all taxa. Sponge sex determination relies on a deeply conserved genetic toolkit with sex-specific loci in DNA repair and recombination genes, syntenic across species and traceable to unicellular ancestors, indicating that core components of sexual reproduction predate animals. We also uncover a younger metazoan-specific complement and show independent evolution of XY and ZW systems, revealing recurrent shifts in heterogamety.
