Procreating through sexual reproduction is, in most cases, highly beneficial, but the main characteristic of this reproductive strategy is the necessary presence of two sexes. The competition for resources, the risk of predation, the energy expenditure involved in searching for and courting a mate mean that many animal species have evolved to facilitate this entire process.
In this article on our site we will see the meaning of sexual dimorphism in animals, what factors cause it and what function they have according to the different species.
What is sexual dimorphism?
Sexual dimorphism are the characters that differentiate one sex from another between animals and plants. As a concept defined by the human being, only those species whose males and females we can differentiate with the naked eye will have sexual dimorphism. If this dimorphism is only determined by pheromones or odors given off by the different genders and not by a visual trait, it will not be called dimorphism for humans.
Sexual dimorphism expressed as differences in size and morphology between the sexes is widespread in the animal kingdom. Charles Darwin realized this and tried to explain it through various hypotheses. On the one hand, he said that sexual dimorphism was for sexual selection, with dimorphism being an advantage, for example, for males competing with each other for females. Another hypothesis that complements the previous one is that sexual dimorphism, in addition to serving in sexual selection, may have evolved as a competition for food or for resources in general.
It should be taken into account that in many cases this sexual dimorphism makes the individual that carries it more striking and, therefore, more likely to be preyed upon.
Factors that cause sexual dimorphism in animals
The main factor causing sexual dimorphism is genetics, usually expressed by the sex chromosomes. In most cases of sexual dimorphism in vertebrate animals, females have two X chromosomes and males have one X and one Y chromosome, which determines that they are born as such. In many invertebrate species, females will only have one sex chromosome and males two.
Another important factor is hormones Each sex differs from each other by different concentrations of certain hormones. Also, during embryonic development, in certain species, a high concentration of testosterone in the brain will cause the brain to develop as female.
Food is also essential for the correct development of the secondary sexual characteristicsthat will give rise to dimorphism. A sick and malnourished animal will have poorer dimorphism and will most likely not attract the opposite sex.
The season of the year and the mating season cause dimorphism to appear in certain species that during the rest of the year do not present dimorphism sexual. This is the case for some birds.
Examples of sexual dimorphism in animals
To understand the different types of sexual dimorphism the simplest thing is to observe the courtship of the different species and their way of life.
Examples of sexual dimorphism in polygynous animals
In many cases, sexual dimorphism can be explained as competition for females. This occurs in polygynous animals (groups of females with one or few males). In these cases the males have to compete to be able to copulate with the females, this makes them bigger, corpulent and stronger than them. In addition, they usually have some organ that serves as a defense or offense. This is the case, for example, of the following animals:
- Deer
- Elephants
- Antelopes
- Chimps
- Gorillas
- Peacocks
- Grouse grouse
- Boars
Examples of sexual dimorphism in animals to differentiate between them
In other animals, dimorphism exists so that males and females of the same species can distinguish each other. This is the case of los parakeets The sexual dimorphism in these birds is found in the beak, in a specific area called “wax”. They have it more brown and rough and they are smooth and blue. Well, if a female's cere is painted blue, she will be attacked by males, and if a male is painted brown, she will be courted as a female.
Examples of sexual dimorphism in animals by sexual performance
Another example of sexual dimorphism is given by sexual performance in the species. Thus, toads and frogs males that tend to embrace females during copulation have stronger and more developed arms, and may also have thorns on their hands to hold on better.
Dimorphism can also be used as a element of courtship This is the case of birds of paradise These birds have no natural predators in their place of origin, so having very striking plumage, long tail or head feathers does not make them more susceptible to predation, but it does It is a good claim for females. This plumage is not only attractive to females, but also gives her information about the male's he alth status and the possibility of having he althy offspring.
Examples of sexual dimorphism in animals where females are larger
Females of raptors, such as eagles, harriers, owls or hawks, are larger than males, sometimes much larger large. This is because it is usually the female that spends more time in the nest incubating the eggs, so having a larger size will help her defend the nest. Also, these females are usually more aggressive and territorial than males, so their large size helps.
In the group of arthropods, females tend to be infinitely larger than males, as is the case with spiders, mantises religious, flies, mosquitoes, etc. The same occurs in amphibians and reptiles, where the females are also larger.
Other examples of sexual dimorphism in animals
There are also very specific cases such as the hyenas The females, before giving birth, are almost indistinguishable from males They have a clitoris as large as the penis of males, the lips are extended and resemble a scrotal sac. After giving birth, the nipples are noticeable, so they can be recognized. In addition, they are much larger than the males, this is because they are cannibalistic animals and any male could try to eat a newborn pup. To avoid this, the greater corpulence and strength of the female is necessary.
Human sexual dimorphism
Human beings also exhibit sexual dimorphism, although some studies suggest that there is no severe feminization or masculinization and that humans tend to to a unification of sexual characteristics, that is, in our species there are more or less masculinized men and more or less feminized women. It is the cultural standards and canons of beauty that lead us to a culture of sexual differentiation.
Arriving at puberty, women and men begin to develop their sexual organs, visually different from each other. Hair appears in the armpits, pubes, face, legs and other parts of the body. Men, by genetics, tend to have more hair on the face and other areas of the body, but many are not like that. Women also have hair on the upper lip.
An exclusive feature of women is the development of the mammary glands, regulated by genetics and hormones, although not all have the same degree of development.
