The vast majority of eukaryotic organisms reproduce sexually, yet the nature of the sexual system and the
mechanism of sex determination often vary remarkably, even among closely related species. Some species
of animals and plants change sex across their lifespan, some contain hermaphrodites as well as males and
females, some determine sex with highly differentiated chromosomes, while others determine sex
according to their environment. Testing evolutionary hypotheses regarding the causes and consequences of
this diversity requires interspecific data placed in a phylogenetic context. Such comparative studies have
been hampered by the lack of accessible data listing sexual systems and sex determination mechanisms
across the eukaryotic tree of life. Here, we describe a database developed to facilitate access to sexual
system and sex chromosome information, with data on sexual systems from 11,038 plant, 705 fish,
173 amphibian, 593 non-avian reptilian, 195 avian, 479 mammalian, and 11,556 invertebrate species.