Tree of Sex: a database of sexual systems

Abstract

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.

Figure 1. Distribution and sample of plant data from the Tree of Sex Database.

Tree structure is derived from taxonomy, where each tip represents all species in a single genus. Diploid chromosome number is indicated by the height of the innermost ring; all other rings indicate the presence or absence of the trait named at the base of the ring. The ‘Other’ ring includes the states: apomictic, gynomonoecy, andromonoecy, polygamodioecy, and polygamomonoecy. The sexual trait data displayed in the rings is based on 11,038 plant entries.

Figure 2. Distribution and sample of invertebrate data from the Tree of Sex Database.

The XY/ZW ring is colored blue for XY and red for ZW taxa. Complex SCS indicates species with complex sex chromosome karyotypes (e.g., X₁X₂Y). The sexual trait data displayed in the rings is based on 11,556 invertebrate entries. Remaining features as in Figure 1.

Figure 3. Distribution and sample of vertebrate data from the Tree of Sex Database.

The ‘Other’ ring includes parthenogenesis, gynogenesis, and hybridogenesis. The XY/ZW ring is colored blue for XY and red for ZW taxa. The sexual trait data displayed in the rings is based on 2,145 vertebrate entries. Remaining features as in Figures 1 and 2.