The 8 types of reproduction and their characteristics

Natural selection bases its evolutionary mechanism on a specific key concept: all living beings have as their goal first and foremost. reproducing itself, since leaving a genetic imprint on future generations is always more important than the life of the individual.

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

These initial concepts make it clear to us 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 they are the types of reproduction of living beingsWell, we assure you that some evolutionary strategies will surprise you.

• Related article: "The 4 types of sex cells"

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 parents, in order to perpetuate his lineage in time. We are facing a primal phenomenon, so much so that, until now, there is no living being in 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, the sexual selection (a variant of natural selection) drives competition between individuals of the same species to achieve the chimera of any living being: leave your genetic imprint on later generations.

Next we will see the different types of reproduction divided into two blocks (sexual and asexual), with concrete examples and their evolutionary implications. Let's go there.

1. 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" reproduction, since in general does not require specialized cells (gametes). In most cases, one stem cell gives rise to two or more daughter cells. As simple as that. Next, we present the different events comprised within asexual reproduction.

1.1 Binary fission

Beings as primal as bacteria and archaea carry it out. In this case, the DNA of the progenitor cell is duplicated and its cytoplasm divides, in order to give rise to two equal daughter cells.

1.2 Budding

We are facing a concept 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 parent organism which, over time necessary and growth, give rise to autonomous entities that can separate from the parental organism (or remain attached to he). An example of this is the species Hydra oligactis, a hydrozoan a few millimeters long with tentacles.

1.3 Sporulation

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

1.4 Fragmentation

We are facing a fascinating case, then the parent can be divided into segments and, from these, autonomous descendants emerge. These body excisions can occur by accident (architomy) or spontaneously (paratomy). Planarians and various starfish exhibit this type of reproduction, for example.

1.5 Polyembryony

We enter 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 reproduction mechanism that we are going to see that does require sexual cells (even if it is a partially asexual method of reproduction).

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

1.6 Parthenogenesis

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

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2. Sexual reproduction

Sexual reproduction necessarily implies syngamy, that is, 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 another from the father's sperm (n). The key to sexual reproduction is, therefore, the genetic variability of the offspring.

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

2.1 Isogamy

The two gametes that unite to give rise to the zygote are exactly the same in structure, size, and internal physiology.. For this reason, a distinction cannot be made between "female gamete" and "male gamete". It is typical of some plants, fungi and protozoa.

2.2 Anisogamy

It is the 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 fertilization process.

• You may be interested in: "The theory of biological evolution: what it is and what it explains"

Differential keys at the evolutionary level

Beyond a classification criterion, we are going to allow ourselves to close this space with a series of biological ramblings that, of course, are of utmost importance to know the reason for the variability of reproductive strategies in the Land.

Asexual reproduction is certainly simpler than sexual reproduction: it is quick and simpleas specialized sex cells do not have to be produced (in most cases). On the other hand, a single individual can give rise to fully functional offspring, that is, it does not require energy expenditure to find and court another conspecific. Of course, it would make sense for all living things to opt for it, right?

Although the origin of sex cannot be experimentally proven and explained is extremely complex, the maintenance of the same in the evolution of living beings can be explained, in part, by the need to adaptation. Sexual selection is clearly biased, as individuals who reproduce are the fittest and, therefore, they will contribute their advantageous characteristics to the following generations.

Thus, a series of characters that have arisen as independent mutations in various living beings can end up merging into one after several generations through 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.

Besides all this, sexual reproduction allows for enormous genetic variation at the individual level, promoting greater adaptability to various environmental changes at the population level.

As clear as all this may seem, explaining long-term maintenance of sex is a real puzzle. This is because, despite the genetic benefits that this entails, the generations of individuals asexuals grow much faster and can also have genetic mutations (although there is no recombination). This, in a theoretical framework, would make asexual reproduction always "win" from a resource optimization point of view.

Furthermore, if asexual reproduction were really deleterious due to the lack of genetic variability that this entails, why do there continue to be species that have practiced it for thousands of years, which have not been extinct? Of course, giving an inalienable answer on this issue is, today, an impossible task.

Summary

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

Bibliographic references:

• García Leal, A. (2006). Ideological biases in theories about the evolution of sex. Autonomous University of Barcelona,.
• Sexual reproduction, ECUred. Picked up on October 31 at https://www.ecured.cu/Reproducci%C3%B3n_sexual#:~:text=En%20la%20reproducci%C3%B3n%20sexual%20se, a% 20new% 20c% C3% A9lula% 20 called% 20zygote.
• Theme: reproduction. AUTONOMOUS UNIVERSITY OF THE STATE OF HIDALGO. Picked up on October 31 at https://www.uaeh.edu.mx/docencia/P_Presentaciones/prepa_ixtlahuaco/2017/biologia.pdf
• Types of reproduction, webcolegios.com. Picked up on October 31 at https://www.webcolegios.com/file/cfaf60.pdf