Understanding protandry and protogyny requires an understanding of the concept of sequential hermaphroditism, which takes place when an animalor organism changes from male to female and vice versa at any time in its life. Protandry and protogyny are the two basic types of sequential hermaphroditism.
Changing from male to female is known as protandy while changing from female to male is known as protogyny. Protrandrous hermaphroditism is when an animal or organism changes from male to hermaphrodite while protogynous hermaphroditism is when it changes from female to hermaphrodite.
Sequential hermaphroditism also occurs in plants, in which case it is called dichogamy.
In animals, protandry occurs when an organism starts out as a male and then changes into a female. The gender change is often due to social pressure. Protandry also takes place in hermaphrodites where before eggs are produced, mature sperms develop first. Such is the case in some crustaceans and earthworms.
In plants, protandry occurs when the male flower parts mature before the female flower parts. It can also happen when the male flower (androecium) matures first and the female flower (gynoecium) matures subsequently. Protandry encourages cross pollination while keeping the plant from pollinating itself.
In animals, protogyny occurs when an organism starts out as a female and then changes into a male. The gender change is prevalent in fish species where a dominant male controls and determines breeding. It can also happen when the male reproductive organs mature after the female reproductive organs do.
In plants, protogyny occurs when the gynoecium or female flower parts mature before the androecium or male flower parts do. Protogyny also promotes cross pollination.
Summary of differences:
Organisms such as some species of fish, gastropods, and plants go through protandry and protogyny – the two basic types of sequential hermaphroditism. In animals, protandry and protogyny take place due to social pressure or according to what the dominant male dictates. In plants, protandry and protogyny take place in order to encourage cross pollination as well as to keep the plants from pollinating themselves.