The 8 types of reproduction and their characteristics

A summary of the main types of reproduction studied in biology.

Natural selection bases its evolutionary mechanism on a specific key concept: all living beings have as their first and last aim to reproduce, since leaving a genetic imprint on future generations is always more important than the individual's own life.

All species present on the planet (except human beings) operate under this dogma, since survival, existence itself, is only conceived as the time interval between reproductive episodes. An animal does not exist because it enjoys it (at least as far as we know), but maximizes its permanence on Earth only in order to leave more offspring.

These initial concepts make clear the importance of reproduction in nature, but do you know what types exist in the animal, plant and microscopic world? Do you know to what extent animals give their lives for their offspring? Let's see what are types of reproduction of living beingsWe assure you that some evolutionary strategies will surprise you.

Types of reproduction: living by and for the offspring.

We can define reproduction, in a general way, as a Biological process that allows the creation of new living beings from one or more progenitors, in order to perpetuate their offspring.in order to perpetuate their lineage over time. This is a primal phenomenon, so much so that, up to now, there is no living being under natural conditions that does not reproduce in some way.

From an evolutionary point of view, reproduction promotes various behavioral and physiological mechanisms in living beings, for example, sexual selection (a variant of natural selection) drives competition between individuals of the same species to achieve the chimera of any living being: to leave its genetic imprint on subsequent generations..

We will now look at the different types of reproduction divided into two blocks (sexual and asexual), with concrete examples and their evolutionary implications. Let's move on.

Asexual reproduction

Asexual reproduction is that in which a living being is produced from a single cell or a group of cells. From a more general point of view, we can define it as the most "basic" form of reproduction, since in general does not require specialized cells (gametes).. In most cases, a mother cell gives rise to two or more daughter cells. It's as simple as that. Here are the different events involved in asexual reproduction.

1.1 Binary fission

Binary fission is carried out by such primitive beings as bacteria and archaea. In this case, the DNA of the progenitor cell is duplicated and its cytoplasm dividesin order to give rise to two identical daughter cells.

1.2 Gemination

This concept is similar to the previous one, but in this case, the division is unequal.. This reproductive mechanism is based on the emergence of prominences in the progenitor organism which, with the necessary time and growth, give rise to autonomous entities that can separate from the parental organism (or remain attached to it). An example of this is the species Hydra oligactis, a hydrozoan of a few millimeters with tentacles.

1.3 Sporulation

Typical of some fungi and bacteria. In these cases, spores are generated (either unicellular or multicellular) which can be released into the environment and which, inside, contain the genetic information necessary to give rise to a new individual.

1.4 Fragmentation

This is a fascinating case, because the progenitor can be divided into segments and, from these, autonomous offspring can arise. These body splits can occur by accident (architomy) or spontaneously (paratomy). Planarians and various sea stars, for example, show this type of reproduction.

1.5 Polyembryony

We are entering more complex terrain, and therefore, from now on, we will observe these types of reproduction in groups of vertebrates, among other living beings. Polyembryony is the first mechanism of reproduction that we are going to see that does require sex cells (although it is a partially asexual method of reproduction).

In this case, two or more embryos develop from a single zygote.. Strictly speaking, this process requires a sexual component (since the zygote is produced by the fertilization of an egg), but, later on, it divides asexually. Univitelline twins in humans are a clear example of this process.

1.6 Parthenogenesis

Parthenogenesis is the ultimate form of asexual reproduction, in which an egg gives rise to an egg cell. an egg cell gives rise to a fully functional living being without the need for prior fertilization.. Species such as the lizard Cnemidophorus neomexicanus are composed solely of parthenogenetic females, as they do not require males to give rise to offspring.

Sexual reproduction

Sexual reproduction necessarily involves syngamy, i.e., the fusion of male and female gametes to produce a zygote.from which an embryo will develop.

Unlike the opposite case, in this phenomenon the progeny is a result of the combination of the genetic information of the father and the mother, since a diploid cell has a double number of chromosomes (2n), where one comes from the mother's egg (n) and the other from the father's sperm (n). The key to sexual reproduction is therefore the genetic variability of the offspring.

In general, sexual reproduction is not usually distinguished in the same way as the asexual variant, but depending on the morphological characteristics of the gametes, we can appreciate two different variants. We will tell you about them below.

2.1 Isogamy

The two gametes that unite to form the zygote are exactly the same in structure, size and internal physiology.. For this reason, no distinction can be made between "female gamete" and "male gamete". It is typical of some plants, fungi and protozoa.

2.2 Anisogamy

Typical and most widespread sexual reproduction. There are two gametes of different shape and size (an egg and a sperm) that will give rise to the zygote through the process of fertilization.

Differential keys at the evolutionary level

Beyond a classificatory criterion, we will allow ourselves to close this space with a series of biological digressions that, of course, are of utmost importance to understand the reason for the variability of reproductive strategies on Earth.

Asexual reproduction is certainly simpler than sexual reproduction: it is fast and simple, since no reproductive strategies have to be produced.It is quick and simple, since specialized sex cells do not have to be produced (in most cases). On the other hand, a single individual can eventually give rise to fully functional offspring, i.e., it requires no energy expenditure to find and court another conspecific. Of course, it would make sense that all living things would opt for it, wouldn't it?

Although it cannot be experimentally proven and explaining the origin of sex is extremely complex, the maintenance of sex in the evolution of living things can be explained, in part, by the need for adaptation. Sexual selection is clearly biased, since the individuals that reproduce are the fittest and, therefore, will contribute their fitness. and, therefore, will contribute their advantageous characteristics to the following generations.

Thus, a series of characters that have arisen as independent mutations in different living beings can end up being united in a single one after several generations by means of this mechanism. Of course, the intrinsic objective of this process is to increase the biological fitness of the species, accumulating beneficial mutations and discarding deleterious ones.

In addition to all this, sexual reproduction allows for enormous genetic variation at the individual level, which promotes greater adaptability to various environmental changes at the population level. to various environmental changes at the population level.

As clear as all this may seem, explaining the maintenance of sex in the long term is a real puzzle. This is because, despite the genetic benefits involved, generations of asexual individuals grow much faster and may also exhibit genetic mutations (although recombination does not occur). This, in a theoretical framework, would make asexual reproduction always "win" from a resource optimization point of view.

Moreover, if asexual reproduction were really deleterious because of the lack of genetic variability it entails, why do species that have been practicing it for thousands of years still exist and have not become extinct? Of course, to give an inalienable answer to this question is, at present, an impossible task.

Summary

As we have seen in these lines, reproduction encloses an exciting world of terms, considerations and evolutionary hypotheses that dazzle from professional ethologists to the general population. Sex and offspring are the very engine of life.Therefore, all living beings adapt and act accordingly to this primal need throughout their life cycles.

Bibliographical references:

• García Leal, A. (2006). Ideological biases in theories about the evolution of sex. Universidad Autònoma de Barcelona.
• Sexual reproduction, ECUred. Retrieved October 31 from https://www.ecured.cu/Reproducci%C3%B3n_sexual#:~:text=In%20the%20reproduction%20sexual%20reproduction%20is,a%20new%20new%20c%C3%A9lula%20called%20zygote%20zygote.
• Topic: reproduction. UNIVERSIDAD AUTÓNOMA DEL ESTADO DE HIDALGO. Retrieved October 31 from https://www.uaeh.edu.mx/docencia/P_Presentaciones/prepa_ixtlahuaco/2017/biologia.pdf.
• Types of reproduction, webcolegios.com. Retrieved October 31 from https://www.webcolegios.com/file/cfaf60.pdf.