And yet there are animals that change sex – How and why do they do it?

In the 2003 film, Finding Nemo, Marlin loses his wife and offspring, so he decides to search for his only remaining son. In real life, the cartoon’s protagonist, the clownfish, would have abandoned Nemo, found another mate, and probably changed his name.

Clownfish (Amphiprion) form pairs, living together for years in symbiosis with an anemone. As in the Pixar movie script, this species is vulnerable to predation in the wild, so it is common for one to die. When this happens, the fish that managed to survive looks for a new mate. If both prove to be male, the larger of the two permanently changes sex and becomes female, as it is the largest and most dominant in this species.

In nature, sex change is not such a rare phenomenon. About 5% of animal species have this ability, and if we include insects in this equation, this percentage increases to 30%.

There are two types of hermaphrodites: simultaneous hermaphrodites and sequential hermaphrodites. The first group are those that function as both female and male: a classic example is the garden snail, in which pairs mate and fertilize each other. There are also some species that can self-fertilize, such as the tapeworm.

Consecutive hermaphrodites do not produce male and female gametes at the same time, but at different stages of their lives. This is the case with clownfish and also with many invertebrates, such as some cnidarians (a group that includes hydria and jellyfish), sea sponges, annelids, molluscs, starfish, and arthropods. Among vertebrates, sex change is widespread in fish and even occurs in some species of frogs.

Size matters

The main explanation for sex switching in nature is offered by the size advantage hypothesis, according to which successive hermaphroditism is favored in species whose individuals reproduce most efficiently with one sex when young or small and most efficiently with the other gender when older. The timing and direction of sex change depends largely on the mating system of these animals.

An example is fish that live with polygamy, i.e. when one male monopolizes the reproduction of many females. In these cases, the conversion is from female to male. When the fish are small, they have no chance of breeding as males because there will always be another bigger and more dominant rival, so it is better to be female until they too have reached a significant size. This transition from male to female is the most common in fish, having been recorded in 305 of the 450 species considered hermaphrodite.

Trimma okinawae, a polygamous species of orange fish capable of changing sex, inhabits coral reefs near various Japanese islands. At just 30 millimeters long, it is one of the smallest vertebrates in existence and extremely vulnerable to predation. At any time, a larger fish can appear and eat the dominant male, leaving the females unable to reproduce. At least, that would be the case if it weren’t for the possibility that the largest female in the group would then become the new male.

As for the mechanism by which animals change sex, there is enormous diversity, especially depending on how complex their reproductive system is.

There are so many species and the diversity is so great that science has not yet recorded all the ways in which animals change sex. In fact, the oceans still harbor many species, completely unknown to science.

Read the News today and get the latest news.
Follow Skai.gr on Google News and be the first to know all the news.