Hermaphroditism and Sex Transitioning

Individuals that produce gametes of both sexes during their life are hermaphrodites, as opposed to gonochoristic individuals that remain a single sex throughout their adult life and produce only eggs or sperm. Hermaphroditism is a reproductive mode utilized in the majority of plants (more than 95%) and a minority of animals (~5%). Simultaneous hermaphrodites possess male and female reproductive systems that are active at the same time, whereas sequential hermaphrodites present as one sex before transitioning to another. Species may be exclusively hermaphroditic or have a mixture of hermaphrodites and single-sex individuals. The latter group consists of androdioecious species, which are composed of males and hermaphrodites, or gynodioecious species, which are composed of females and hermaphrodites (~1% of the angiosperms). Both groups represent conceptually intermediate stages between exclusive hermaphroditism and gonochorism or dioecy ( Figure 16.1 ). Although the energy costs may be higher than for gonochoristic species, the number of thriving contemporary hermaphroditic species implies clear benefits to this mode of reproduction.