Hermaphroditism

Hermaphroditism
Animals that have both male and female organs in the same individual are called hermaphrodites, and the condition is called hermaphroditism. In contrast to the dioecious state of separate sexes, hermaphrodites are monoecious, meaning that both male and female organs are in the same organism. Many sessile, burrowing, or endoparasitic invertebrate animals (for example, most flatworms, some hydroids and annelids, and all barnacles and pulmonate snails) and a few vertebrates (some fishes), are hermaphroditic. Some hermaphrodites fertilize themselves, but most avoid selffertilization by exchanging germ cells with another member of the same species (Figure 7-3). An advantage is that with every individual producing eggs, a hermaphroditic species could potentially produce twice as many offspring as could a dioecious species in which half the individuals are nonproductive males. In some fishes, called sequential hermaphrodites, the animal experiences a genetically programmed sex change during its life. In many species of reef fishes, for example, the wrasses, the animal begins life as either a female or a male (depending on the species) but later becomes the opposite sex.