Unlike most other sequential hermaphrodites that make the switch and stick with it, hawkfish can switch back again. Female-turned-male hawkfish may revert to female if, say, their new harem loses too many females or if a larger male challenges them.
In animals
Some species exhibit sequential hermaphroditism. In these species, such as many species of coral reef fishes, sex change is a normal anatomical process. Clownfish, wrasses, moray eels, gobies and other fish species are known to change sex, including reproductive functions.
Flexible Fish
Scientists have documented the sex-changing abilities of several fish species, including parrotfish, clownfish and some gobies. Most species capable of changing sex transition from female to male – a pattern called protogyny; however, the opposite pattern – protandry – occurs in a handful of species.
Caltech scientists have discovered a new species of worm thriving in the extreme environment of Mono Lake. This new species, temporarily dubbed Auanema sp., has three different sexes, can survive 500 times the lethal human dose of arsenic, and carries its young inside its body like a kangaroo.
Though scientists are still investigating the specifics of the various species, crocodilians -- including crocodiles, alligators, caimans and gharials -- typically produce inherently female embryos, which can become male when certain environmental conditions are met.
Other scientists believe that the big sharks, like some other species, change sex when they reach a certain size: males become females. The switch may ensure survival by allowing the largest, most experienced sharks to give birth to young.
Researchers have identified more than 500 fish species that regularly change sex as adults. Clown fish begin life as males, then change into females, and kobudai do the opposite. Some species, including gobies, can change sex back and forth. The transformation may be triggered by age, size, or social status.
Reproduction in sharks is equally varied: some lay eggs, but most give birth to live young. Sharks typically give birth after 11–12 months of pregnancy, but some, such as the frilled shark, are pregnant for more than three years. In some sharks, a placenta develops during pregnancy.
Six male sharks found by this researcher turned out to be pregnant.
The mimic octopus has remarkable dexterity, being capable of changing its colour, behaviour, shape and texture, and can alter its mimickry according to the circumstances.
Lycanthropes or werewolves are mythological humans that have the ability to shapeshift into wolves or anthropomorphic wolf-like creatures. They can infect the human population with a bite, and the creature's transformation is often associated with a full moon.
Frogs can change their sex even in pristine, pollution free settings. Past research suggested that male-to-female sex changes happening in frogs in suburban ponds may be caused by increased levels of estrogen released into the water. They found more female frogs than males in suburban areas.
Recent studies (Bergeron et al. 1994, 1999) have shown that polychlorinated biphenyl compounds (PCBs), a class of widespread pollutants that can act like estrogens, are able to reverse the sex of turtles raised at “male” temperatures.
They were ZZs, genetically male, which was the first time sex-switched reptiles had been found in the wild. Holleley's team found that these sex-switched ZZ females could have a huge impact on the population.
Same-sex behaviour ranging from co-parenting to sex has been observed in over 1,000 species with likely many more as researchers begin to look for the behaviour explicitly. Homosexuality is widespread, with bisexuality even more prevalent across species.
At first glance it looks like the single-celled organism Tetrahymena thermophila has cracked this problem in spectacular fashion. It has not two but seven sexes, and each one can mate with any of the others, which opens up the field considerably.
Based on the sole criterion of production of reproductive cells, there are two and only two sexes: the female sex, capable of producing large gametes (ovules), and the male sex, which produces small gametes (spermatozoa).
Introducing Greek Mythology's Stories Of Transformation
The master of shapeshifting in Greek mythology is Proteus, a sea god who constantly changes form and always avoids answering questions. However, transformation is the main subject of many stories in the classical canon.
Therianthropy refers to the fantastical, or mythological, ability of some humans to change into animals. Therianthropes are said to change forms via shapeshifting.
Like many Egyptian gods, Set was capable of shapeshifting. He could turn himself into an ox, an oryx, a hippopotamus, a bull, a crocodile, and a panther. He could also take the form of Anubis.
Sharks can sleep, and often opt to keep their eyes open while they do, according to new research published in Biology Letters. Because some sharks must swim constantly to keep oxygen-rich water flowing over their gills, it has long been rumored that they don't snooze at all.