gonochorism

Gonochorism is a mode of sexual reproduction in which individuals belong to one of two distinct sexes, male or female, and do not change sex during their life. In gonochoric species, reproductive success depends on the presence of both a male and a female for mating. This system is contrasted with hermaphroditism, where organisms possess both male and female reproductive organs or can switch between sexes.

Gonochorism is widespread in the animal kingdom, including most mammals and birds, and many reptiles and fishes. In plants, a closely related condition is called dioecy, where separate male and female individuals exist. The mechanism of sex determination varies: many taxa use genetic sex determination (GSD), such as XY systems in mammals or ZW systems in birds; others rely on environmental sex determination (ESD), where factors like incubation temperature influence the developing sex, though individuals typically remain one sex for life.

Ecological and evolutionary implications of gonochorism include its influence on population structure, mating systems, and sexual selection. Because individuals do not change sex, stable and biased sex ratios can affect mating opportunities and reproductive success. Some gonochoristic species exhibit sexual dimorphism, with differences in size or morphology between males and females that reflect competing reproductive strategies.