Protogyny is a form of sequential hermaphroditism in which an animal changes sex from female to male. Protogynous animals are born female, but at some point in their life cycle, an internal or external trigger causes them to become male. The process differs between species, but has been documented in several types of arthropods including isopods and crustaceans, some species of amphibians, some echinoderms, and a large number of fish.
Other forms of sequential hermaphroditism include protandry, in which the organism changes from male to female, and protogynous or protandrous hermaphroditism, in which the organism changes from female (if protogynous) or male (if protandrous) to a simultaneous hermaphrodite. These conditions are not necessarily mutually exclusive with sexual dimorphism; a species may exhibit both, and the changed individual may take on the hormonal and phenotypic characteristics of its current sex.
While often confused with intersexuality, this is a different and mostly unrelated phenomenon. Protogyny and all other forms of hermaphroditism are also unrelated to gender identity concepts, with which they are often confused by uninformed social critics. An organism is only considered hermaphroditic if it exhibits both male and female primary sexual characteristics as a part of the typical life cycle of its species. An organism that possesses some combination of the two due to an uncommon condition, or one that changes sex due to deliberate intervention, should not be referred to as hermaphroditic.
The phenomenon of protogyny is relevant to the history of de-extinction and genetic engineering, most famously due to the use of genetic structures from the common reed frog (Hyperolius viridiflavus) to complete the deteriorated genomes of extinct animals. The genes sourced from this frog permitted their recipients to become protogynous, changing sex when in a single-sex environment.
The common reed frog, H. viridiflavus, is capable of protogyny and was the first vertebrate animal to be discovered with this ability. A study published in Copeia in 1989 first documented this change; in the experiment, seven out of twenty-four female frogs of this species became males without any hormone treatment. In this species, the change is believed to be triggered by a biochemical cue, which occurs when there are significantly fewer males in the local environment than females. The frogs which became male, called “terminal phase males,” are fully capable of reproducing as males and have functional male reproductive organs which replace the female organs. In the common reed frog, protogyny is an adaptation used to increase the amount of offspring a frog can produce. Most of the frogs die during the dry season, so increasing reproductive output is vitally important to the survival of the species.
Due to the inclusion of H. viridiflavus genetic structures in its genome, at least one Velociraptor antirrhopus subspecies is capable of experiencing protogyny. The coloration of the animal does not immediately change when the biochemical trigger is activated; this makes sexing the apparent females difficult without invasive examination. It is not known if allowing the terminal phase male to survive for a longer period of time would eventually cause its outward appearance to change, as the known terminal phase male specimens died before or during the 1993 incident. Terminal phase males will experience the disintegration of female reproductive organs and the growth of male organs in their place. The male organs are completely functional, and in one case, living offspring were successfully produced in the wild as a result. Protogyny does not appear to have any adverse effect on reproduction in V. antirrhopus, indicating the successful complete integration of common reed frog DNA into its genome. The transformation is believed to be activated by a similar mechanism to H. viridiflavus, occurring when a lack of males in the local environment sets off a biochemical trigger within the animal’s body. Unlike the frog, the dinosaur is fully capable of surviving after breeding, so this ability has a different ultimate function than in the genetic source.
Dr. Alan Grant discovered protogyny in Velociraptor on June 12, 1993 and speculated that amphibian DNA was the cause. This hypothesis was confirmed by InGen geneticist Dr. Henry Wu, who had originally engineered the animal, in November 1994.
Protogyny has only been observed in V. a. nublarensis, but was likely possible in V. a. sornaensis assuming that both were produced at around the same time. As the genes coding for protogyny were inserted into the Velociraptor genome under the assumption that they would not affect the animal’s biology, it is likely that they were replaced by InGen geneticists following the 1994 confirmation of Velociraptor protogyny. Thus, the V. a. masranii subspecies produced in 2012 was probably incapable of protogyny.
Evidence is presented in Jurassic Park: The Game which implies that Dilophosaurus venenifer was able to experience protogyny in a manner similar to Velociraptor antirrhopus. Prior to the inclusion of H. viridiflavus DNA into the de-extinct animals, Dr. Wu had used DNA from the yellow-banded poison dart frog (Dendrobates leucomelas) in Dilophosaurus to no ill effect. Any Dilophosaurus produced before the change, if said change did indeed affect Dilophosaurus, would not have been able to experience protogyny.
While eggs were observed by Nima Cruz on June 11 and Jess Harding on June 12, 1993, Dr. Gerry Harding was apparently unaware of the existence of protogyny in the genetic sources of the dinosaurs and dismissed the eggs as belonging to an extant bird or lizard. The only people involved who actually saw the parent animal, Billy Yoder and Oscar Morales, did not survive the incident or report the eggs to someone who did survive. As a result, dilophosaur protogyny (if it does exist) was not officially discovered, and may still be unknown within the film universe.
The eggs produced during the incident did not survive, as the population remained constant between 1993 and 1994; the cause of death is not known and may have been due to environmental or behavioral factors rather than genetic factors. Since there is no other evidence of H. viridiflavus genes actually being used in Dilophosaurus (only D. leucomelas has been confirmed in official capacity), the eggs may even have been unfertilized and this animal might actually not be capable of protogyny at all.
In older drafts of the Jurassic Park film, Dr. Grant and the Murphy children would have discovered a Gallimimus nest with hatched eggs, thus confirming that Gallimimus were undergoing protogyny in order to breed. However, in the final film, this was replaced with a Velociraptor nest, leaving it unknown whether InGen’s Gallimimus genome contained common reed frog DNA permitting protogyny and thus breeding.