When the female clownfish dies, her mate becomes the new female
A sea anemone usually shelters one large female clownfish, a smaller breeding male and a few even smaller hangers-on. Remove the female and the male changes sex to replace her, while the biggest of the juniors matures into the new breeding male. Clownfish are among some 65,000 animal species that produce both eggs and sperm at some point.
A hermaphrodite is any sexually reproducing organism that makes both male and female sex cells. The name comes from Hermaphroditus, child of Hermes and Aphrodite, who in Ovid's telling merged with the nymph Salmacis. Roughly 5% of animal species are hermaphroditic, or a third if insects, which almost never are, are left out. Among snails, earthworms and sea squirts it is the norm, it turns up in some fish, and no mammal or bird species is known to do it. In flowering plants it dominates: about 94% of species carry both sexes on one plant.
Some species switch sex partway through life. Biologist Michael Ghiselin's size-advantage model explains why: if one sex gains far more offspring once it is large, it pays to become that sex after growing. Clownfish go from male to female. Wrasses mostly go the other way, and they even have two kinds of male, including drab ones that mingle with females. A coral reef goby, Lythrypnus dalli, can switch in either direction depending on whether it behaves dominantly or submissively. The pattern has real-world consequences: fishing that removes big clownfish has pushed populations to change sex at smaller sizes, and farmed groupers that take years to become male make prized breeding stock.
Other species are both sexes at once. Land snails and slugs swap sperm with a partner, and both then lay fertilised eggs. Earthworms carry ovaries and testes but have safeguards against fertilising themselves, while hamlet fish take turns playing each role over several nights. The mangrove killifish is thought to be the only vertebrate that routinely fertilises itself inside its own body.
Appearances can mislead. Early explorers believed spotted hyenas were hermaphrodites because females have an enlarged clitoris resembling a penis, through which they even give birth. They are, in fact, ordinary males and females.
Source: Hermaphrodite
