Arxiu d'etiquetes: clownfish

Sex change is also in animals

Sex change is not only present in humans (known as transexuality), but there are some examples of animals that change sex, that is, they are born male or female, and throughout his life, species change to the opposite sex. Do you want to know some of these species? Remember that you can also read a post in this blog about Homosexuality in animals.


The animal sex change is a fact not very widespread, but is present especially among fish and some mollusks, jellyfishes, crustaceans, echinoderms and worms.

However, in the case of animals, the term used is not transsexuality. The change of sex in the animal kingdom is a particular type of hermaphroditism: sequential hermaphroditism.

This change of sex is usually genetically programmed and  it is influenced by the environment in which it develops. However, at birth they have already both sexes, so that sex determination is not given by the genes.

There are different types of sequential hermaphroditism:

  • Protandry: when an organisms is born male and changes to female, such as the clownfish (Amphip
  • Protogyny: when an organisms is born female and changes to male, such as wrasses.
  • Bidirectional sex change: when an organism has both full female and male sexual organs, but act as a male or female during different stages of its life, such as the  fish Lythrypnus dalli. 

It is clear that this strategy supposes an important benefit in front of other species: in front of extreme conditions, the organisms have the capacity of assuring the future generations by changing their sex.


The clownfish is one of the best known examples of sex change in the animal kingdom. Our friend Nemo, throughout its life will become a female. Clownfishes are all born males, but after a certain age they change sex. They can also change sex in case the female dies, so although Nemo’s mother died, found his mother in his father.

pez payazo cambio de sexo
Couple of clownfishes, with the female bigger than the male (Picture: Georggete Douwma, Arkive).

The form of reproduction of these very colourful and known fishes is most curious: in each anemone, cnidarian animals with which they live in symbiosis, lives a harem, consisting of one female (bigger in size than the male), a reproductive male and several non-breeding males.

Ciclo de vida del pez payaso (Foto: The fisheries blog).
Cycle of clownfish changing sex (Picture: The fisheries blog).

Si la hembra muere, el macho reproductor se transforma en hembra y el macho no reproductor de mayor tamaño madura sexualmente.


Janthinidae is a group of sea-snails with a unique feature: they use their mucus to produce a bubble raft to float in the ocean. Some of them can produce a bubble per minute.

janthina janthina
Violet sea-snail (Janthina janthina) (Picture: Roboastra).

Well, this family of gastropods is made up of individuals who may change sex. Like the clownfish, organisms are born male and then change to female.


The bluestreak cleaner wrasse (Labroides dimidiatus) is a fish in which the sex change is triggered by some behavioural patterns.

Tordo limpiador (Labroides dimidiatus) (Foto: Darwin Books Cats).
Bluestreak cleaner wrasse (Labroides dimidiatus) (Picture: Darwin Books Cats).

There is usually a dominant male that keeps a harem of females, but if he dies, the dominant female will assume the position of the male in a few hours, courting other females although the change of sex can be extended for two weeks.


The common slipper shell (Crepidula fornicata) is a marine snail in which the sex change is produced by the size of the animal. This molluscs are born male but, at a certain size, they become females.

They are very curious snails: they live stacked on the top of other animal, with larger organisms at the bottom. This means that the individual of the base is a female and males are above. Thus, when the female dies, the larger male becomes the female of the group.

crepidula fornicata
Common slipper shell (Crepidula fornicata) (Picture: Dr. Keith Hiscock).

It is an exotic species in Spain, which could be living in the whole Galician coast. Anyway, its natural distribution area is North America.


Until now, we have explained species that live far from the place we life, but the truth is that this behaviour also happens in some Mediterranean species. Some examples are the starlet cushion star (Asterina gibbosa) and the ornate wrasse (Thalassoma pavo).

The ornate wrasse is one of the most colourful fishes in the Mediterranean sea. In that case, they are born females, but according to the sex ratio, they can change to males.

pez verde thalassoma pavo
Ornate wrasse (Thalassoma pavo) (Picture: Matthieu Sontag, Creative Commons).


If you are one of those who thing that sex change in human beings is unnatural, you have read some examples of animals that change their sex.

All you need is Biology is a LGTB-friendly blog and we love everbody equally. More love and respect, and less hate!



Symbiosis: relationships between living beings

Predation, parasitism, competition… all living beings, besides interacting with the environment, we relate to other living beings. What types of relationships in addition to those you know? Do you feel like to know them?


The group of all living beings in an ecosystem is called biocenosis or community. The biocenosis is formed in turn by different populations, which would be the set of individuals of the same species occupying an area. For survival, it is imperative that relations between them are established, sometimes beneficial and sometimes harmful.


They are those that occur between individuals of different species. This interaction it is called symbiosis. Symbiotic relationships can be beneficial to a species, both, or harmful to one of the two.

Detrimental to all the species involved:

Competition: occurs when one or more resources are limiting (food, land, light, soil …). This relationship is very important in evolution, as it allows natural selection acts by promoting the survival and reproduction of the most successful species according to their physiology, behavior …

Las selvas son un claro ejemplo de competencia de los vegetales en busca de la luz. Selva de Kuranda, Australia. Foto de Mireia Querol
Rainforests are a clear example of competition between vegetals in the search for light. Kuranda rainforest, Australia. Photo by Mireia Querol
One species has benefits and the other is detrimented:
  • Predation: occurs when one species (predator) feeds on another (prey). This is the case of cats, wolves, sharks
foca, león marino,
Great white shark (Carcharodon carcharias) jumping to depretade a marine mamal, maybe a sea lion. Photo taken from HQ images.
  • Parasitism: one species (parasite) lives at the expense of other (host) and causes it injury. Fleas, ticks, pathogenic bacteria are the best known, but there are also vertebrate parasites, like the cuckoo that lay their eggs in the nests of other birds, which will raise their chicks (brood parasitism). Especially interesting are the “zombie parasites”, which modify the behavior of the host. Read this post to learn more!
    Carricero (Acrocephalus scirpaceus) alimentando una cría de cuco (Cuculus canorus). Foto de Harald Olsen
    Reed warbler (Acrocephalus scirpaceus) feeding a cuckoo’s chick (Cuculus canorus). Photo by Harald Olsen

    Parasites that live inside the host’s body are called endoparasites (such as tapeworms), and those who live outside ectoparasites (lice). Parasitism is considered a special type of predation, where predator is smaller than prey, although in most cases does not cause the death of the host. When a parasite causes illness or death of the host, it is called pathogen.

    Cymothoa exigua es un parásito que acaba sustituyendo la lengua de los peces por su propio cuerpo. Foto de Marcello Di Francesco.
    Cymothoa exigua is a parasite that replaces the tongue of fish with their own body. Picture by Marcello Di Francesco.

Kleptoparasitism is stealing food that other species has caught, harvested or prepared. This is the case of some raptors, whose name literally means “thief.” See in this video a case of kleptoparasitism on an owl:

Kleptoparasitism can also occur between individuals of the same species.

One species has benefits and the other is not affected:
  • Commensalism: one species (commensal) uses the remains of food from another species, which does not benefit or harm. This is the case of bearded vultures. It is also commensalism the use as transportation from one species over another (phoresy), as barnacles attached to the body of whales. The inquilinism is a type of commensalism in which a species lives in or on another. This would apply to the woodpeckers and squirrels that nest in trees or barnacles living above mussels. Finally, metabiosis is the use of the remains of a species for protection (like hermit crabs) or to use them as tools.
    El pinzón carpintero (Camarhynchus pallidus) utiliza espinas de cactus o pequeñas ramas para extraer invertebrados de los árboles. Foto de
    The woodpecker finch (Camarhynchus pallidus) uses cactus spines or small branches to remove invertebrates from the trees. Picture by Dusan Brinkhuizen.
    Both species have benefits:
  • Mutualism: the two species cooperate or are benefited. This is the case of pollinating insects, which get nectar from the flower and the plant is pollinated. Clownfish and anemones would be another typical example, where clown fish gets protection and food scraps while keeps predators away and clean parasites of the sea anemonae. Mutualism can be optional (a species do not need each other to survive) or forced (the species can not live separately). This is the case of mycorrhizae, an association of fungi and roots of certain plants, lichens (mutualism of fungus and algae), leafcutter ants

    Las hormigas Atta y Acromyrmex (hormigas cortadoras de hogas) establecen mutualismo con un hongo (Leucocoprinus gongylophorus), en las que recolectan hojas para proporcionarle nutrientes, y ellas se alimentan de él. Se trata de un mutualismo obligado. Foto tomada de Ants kalytta.
    Atta and Acromyrmex ants (leafcutter ants) establish mutualism with a fungus (Leucocoprinus gongylophorus), in which they gather leaves to provide nutrients to the fungus, and they feed on it. It is an obligate mutualism. Photo taken from Ants kalytta.


They are those that occur between individuals of the same species. They are most beneficial or collaborative:

  • Familiars: grouped individuals have some sort of relationship. Some examples of species we have discussed in the blog are elephants, some primates, many birds, cetaceans In such relationships there are different types of families.
  • Gregariousness: groups are usually of many unrelated individuals over a permanent period or seasonal time. The most typical examples would be the flocks of migratory birds, migration of the monarch butterfly, herds of large herbivores like wildebeest, shoal of fish

    El gregarismo de estas cebras, junto con su pelaje, les permite confundir a los depredadores. Foto tomada de Telegraph
    Gregariousness of these zebras, along with their fur, allow them to confuse predators. Photo taken from Telegraph
  • Colonies: groups of individuals that have been reproduced asexually and share common structures. The best known case is coral, which is sometimes referred to as the world’s largest living being (Australian Great Barrier Reef), but is actually a colony of polyps (and its calcareous skeletons), not single individual.
  • Society: they are individuals who live together in an organized and hierarchical manner, where there is a division of tasks and they are usually physically different from each other according to their function in society. Typical examples are social insects such as ants, bees, termites

Intraspecific relations of competition are:

  • Territorialityconfrontation or competition for access to the territory, light, females, food can cause direct clashes, as in the case of deer, and/or develop other strategies, such as marking odor (cats, bears), vocalization

    Tigres peleando por el territorio. Captura de vídeo de John Varty
    Tiger figthing for territory. Video caption by John Varty
  • Cannibalism: predation of one individual over another of the same species.

And you, as a human, have you ever thought how do you relate with individuals of your species and other species?