One of the essential features of living beings is the ability to reproduce, to produce new beings with characteristics similar to their own. The strategies used by living beings to consummate the mission of reproduction are varied. Sexual Reproduction in Animals is a complex process of hormonal changes that lead to the mating of male and female with a single purpose: to perpetuate the species.
Sexual Reproduction in Animals
Animals, as individual creatures, appear and disappear, but the species of which it is a part remains, all by virtue of reproduction, one of the basic functions of living beings. The process of replication of living beings, called reproduction, is one of their most important characteristics. It forms new organisms, which can replace those that have deteriorated or died.
As part of the animal kingdom we can differentiate two reproductive strategies, asexual reproduction and sexual reproduction, which is the most widespread among animals. Compared to asexual reproduction, sexual reproduction has some disadvantages, among which stand out: a higher energy consumption in the search and dispute to find a mate, a slower reproduction speed and a smaller number of descendants, among others.
Sexual reproduction is the characteristic reproductive strategy of animals, despite the fact that some of them can reproduce exceptionally through an asexual strategy. Therefore, in this article we will dedicate ourselves to explaining what the sexual reproduction of animals consists of.
Features
Sexual reproduction is the reproductive tactic practiced by numerous animals and plants to give rise to new individuals that make the species endure. The particularities that determine this kind of reproduction are diverse. In animals, reproduction can vary according to the complexity that living beings develop. From unicellular beings to invertebrate animals and later to vertebrates, asexual reproduction is extinguished until only sexual reproduction remains.
While only sexual reproduction is maintained, a more complex behavior is also developed in order to achieve reproduction. This behavior involves mating ceremonies in the form of fights, songs, skills, etc. that will cause certain individuals to reproduce and others not, and they will not necessarily be the strongest.
As a first point, in sexual reproduction there are two entities involved, a female and a male, in contrast to asexual reproduction, which is only one. Both males and females have organs that we know as gonads that generate gametes. These gametes become the sex cells, ovules in females, produced by the ovaries, and sperm produced by the testicles in males.
When an egg and a sperm fuse, they give rise to a zygote. This alliance is called fertilization. Fertilization can be produced inside or outside the animal, depending on the species, in such a way that there is external fertilization in which males and females expel their gametes into the aqueous medium to be fertilized and internal fertilization, in which sperm they get the ovum inside the female.
After fertilization, the formed zygote will be made up of 50% maternal DNA and 50% paternal DNA, that is, the offspring that will be produced through sexual reproduction will have genetic material from both parents.
Steps
Sexual reproduction in animals is made up of several phases, beginning with gametogenesis. This process lies in the conformation and development of the female and male gametes inside the female and male gonads respectively.
Starting from germ cells and through a type of cell division known as meiosis, both males and females form their gametes. The rate of formation and maturation of the gametes will depend on various factors but, primarily, on the species and sex of the subject to be engendered.
After gametogenesis, the mechanism by which fertilization is produced is copulation. Controlled by hormones, individuals of childbearing age will seek the company of the opposite sex for mating and, after courtship, copulation will take place in animals that have internal fertilization. Species with external fertilization will release the gametes into the environment to be fertilized.
After fertilization occurs the last stage of sexual reproduction, fertilization, which is based on a succession of molecular changes that allow the fusion of the nucleus of the egg with the nucleus of the sperm.
Types of Sexual Reproduction
The kinds of sexual reproduction that exist in animals are associated with the size of the gametes that are going to fuse in fertilization, among them they differ: isogamy, anisogamy and oogamy.
- Isogamy is the union of two gametes of similar size, it is not possible to distinguish visually which is the male or female gamete. Both can be mobile or immobile. This is considered the first kind of sexual reproduction that made its appearance in evolutionary history and is characteristic of chlamydomonas (unicellular algae) and monocystis, a protist. It does not manifest in animals.
- Anisogamy is the union of gametes of different sizes. There are distinctions between male and female gametes, and the two can be motile or immotile. It arises later in evolution than isogamy. It manifests itself in fungi, higher invertebrates and other animals.
- Oogamy is the union of a huge, nonmotile female gamete with tiny, motile male gametes. It is the last kind of reproduction that arises in evolution. It is common in higher algae, ferns, gymnosperms and species such as vertebrates.
Examples
There are numerous examples of sexual reproduction as animal species are known.
- Mammals such as dogs, primates, whales or humans have sexual reproduction with internal fertilization and oogamy, they are also viviparous animals, so the development of the embryo will take place in the womb.
- Birds, although they release eggs like all oviparous animals, also follow this sexual reproductive tactic with oogamy.
- Reptiles, amphibians and fish also reproduce sexually, although some species follow an asexual strategy at certain stages of their existence. While some are oviparous, others are ovoviviparous, most of them have external fertilization and many others internal.
- Arthropods are a large and diverse group of animals, so in this group we will get both internal and external fertilization and cases of oogamy and anisogamy. A few of them reproduce asexually.
Keep in mind that there are hermaphrodite animals, with female and male reproductive organs at the same time, but they can only behave as female or male at the time of mating. Self-fertilization does not take place.
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