Sexual Reproduction in Animals - Embibe
  • Written By Sumana_C
  • Last Modified 27-06-2022
  • Written By Sumana_C
  • Last Modified 27-06-2022

Sexual Reproduction in Animals: Detailed Explanation

Sexual Reproduction in Animals: Students must know about sexual reproduction in Animals, both asexual and sexual reproduction, as some animals produce offspring through sexual reproduction. In contrast, others produce offspring through asexual reproduction. These methods have both disadvantages and advantages.

On the other hand, a large number of offspring can be produced asexually quickly. So these two are the most significant advantages asexually reproducing organisms have. These two advantages are not found in sexually producing organisms. If it is a predictable or stable environment, the most effective means of reproduction is asexual reproduction. That is because all the offspring will be adapted to that particular environment. On the other hand, if it is an unpredictable and unstable environment, asexual reproduction will be disadvantaged for species because offspring will be genetically identical and may not be adapted to different conditions.

Sexual Reproduction in Animals: Asexual Reproduction

Asexual reproduction produces genetically identical offspring to the parent. That is because all these offspring produced by asexual reproduction are the clones of the parent. An individual can produce offspring asexually. Asexual reproduction happens in prokaryotic microorganisms, especially archaea and bacteria, and many eukaryotic, single-celled, and multi-celled organisms. Animals can reproduce asexually in several ways. However, the details of which vary from one species to another.

Sexual Reproduction in Animals: Fission

Some invertebrate multicellular creatures engage in fission, commonly known as binary fission. It resembles the binary fission process that occurs in single-celled prokaryotic organisms in several aspects. When an organism appears to split into two parts and, if necessary, regenerates the missing parts of each new organism, the phenomenon is referred to as fission.

For instance, some turbellarian flatworm species, sometimes known as planarians, like Dugesia dorotocephala, can split their bodies into head and tail sections, and each of the two new individuals can subsequently regenerate the missing half. The genus Holothuria’s sea anemones (Cnidaria) of the genus Anthopleura and sea cucumbers (Echinodermata) will split into two halves across the oral-aboral axis. After that, it will regenerate the other half in each resulting individual.

Budding

Budding is an asexual reproduction form that happens because of the outgrowth of a body part that leads to the separation of the “bud” from the original organism. As a result, two individuals originate, one smaller than the other. Budding appears commonly in invertebrate animals like corals and hydras. A bud forms in hydras that develop into an adult and break away from the main body.

Hydra reproduces asexually basically through budding. An adult hydra’s tubular body develops into a bud, sprouting a mouth and tentacles before separating from its parent. The brand-new hydra is fully formed and will choose a place to attach itself. Some corals, like the Lophelia pertusa in this image, have the ability to budding. This depicts a hydra with a body resembling a stalk and tentacles extending from the top. A smaller hydra is sprouting from the stalk’s side.

Fragmentation

An individual gets broken up into pieces during fragmentation, and then they are rebuilt. A distinct individual will reappear from each section of the animal if it can be divided into pieces and the pieces are large enough. Fragmentation can happen accidentally, as a result of predator damage, or as a result of natural reproduction. Fragmentation-based reproduction can be seen in sponges, some cnidarians, turbellarians, echinoderms, and annelids.

In some sea stars, a damaged arm and a fragment of the central disc can be used to create a new individual. This sea star is in the process of developing a full sea star from a severed arm. Fisheries workers have been known to cut sea stars in half and throw them back into the water to destroy the creatures consuming their clam or oyster beds. The two portions can each regenerate a new half, which is unfortunate for the workers because there will be twice as many sea-stars to eat the oysters and clams.

Parthenogenesis

Parthenogenesis is an asexual reproduction form in which an egg becomes an individual without being fertilized. That particular offspring can be either diploid or haploid, and it depends on the process in the species. Parthenogenesis happens in invertebrates like rotifers, water fleas, aphids, ants, stick insects, bees, and wasps. Ants, wasps, and bees use parthenogenesis to produce haploid males, known as drones. The diploid females, queens, and workers resulting from a fertilized egg.

Some vertebrate animals like amphibians, reptiles, and fish also reproduce through parthenogenesis. We can find parthenogenesis in species where the sexes were separated in terrestrial or marine zoos. If females are separated from males, two female Komodo dragons, a blacktop shark and a hammerhead shark, produce parthenogenic young. It is possible that the asexual reproduction observed occurred due to distinctive circumstances. Otherwise, it will not occur.

Sexual Reproduction in Animals

Two people’s reproductive cells are combined to create genetically distinct kids through sexual reproduction. Having separate sexes or both sexes in one individual, for example, can change the characteristics of the individuals that create the two types of gametes. Sex determination, the process through which a person’s sex identity develops, can also differ. During sexual reproduction, the genetic material of two individuals is combined to create genetically unique offspring that are distinct from their parents.

Sexually reproducing individuals are believed to be more fit due to the genetic diversity of their progeny since more of them may survive and reproduce in an unpredictably changing environment. Males and females must be kept in separate populations for a species to reproduce sexually and have distinct sexes.

Hermaphroditism

Animals with one individual possessing both male and female reproductive systems are said to be hermaphrodites. Hermaphrodite invertebrates include snails, earthworms, slugs, tapeworms, and others. Although hermaphrodites can self-fertilise, they usually mate with a member of their species to fertilise and produce offspring together. Animals with little or no movement, like barnacles and clams, are more likely to self-fertilise. Because self-fertilisation is an extreme form of inbreeding and typically results in less fit offspring, many animals have specialised systems to avoid it.

Sexual Reproduction in Animals: Sex Determination

Mammalian sex is specified genetically by the combination of X and Y chromosomes. Heterozygous individuals (XY) are male, while individuals homozygous for X (XX) are female. The presence of a Y chromosome results in the development of male characteristics in mammals, while its absence causes female characteristics. The XY system can also be found in some plants and insects.

Bird sex determination depends on the combination of W and Z chromosomes. Males are produced when Z is homozygous (ZZ), while females are produced when Z is heterozygous (ZW). Because the female in birds is the sex with the distinct sex chromosomes, it is essential to note that this system is the reverse of the mammalian system. Similar to the Y chromosome in animals, the W chromosome appears crucial in defining an individual’s sex. The ZW system is used by several fish, crustaceans, insects (including butterflies and moths), and reptiles.

There are also ways for determining chromosomal sex that is more complex. One population of swordtail fish, for instance, contains three sex chromosomes.

The environment, instead of genetics, influences some creatures’ sex. For instance, the temperature during the middle third of egg development affects the ability to determine the sex in alligators, certain turtles, and tuataras. Environmental sex determination, or temperature-dependent sex determination, is the term used to describe this. In several turtle species, males are produced when eggs are incubated at cooler temperatures, whereas females are produced when eggs are incubated at warmer temperatures. Some crocodiles and turtles produce males in moderate temperatures, while females are produced in warm and chilly conditions.

The environment, instead of genetics, influences some creatures’ sex. For instance, the temperature during the middle third of egg development affects the ability to determine the sex in alligators, certain turtles, and tuataras. Environmental sex determination, or temperature-dependent sex determination, is the term used to describe this. In several turtle species, males are produced when eggs are incubated at cooler temperatures, whereas females are produced when eggs are incubated at warmer temperatures. Some crocodiles and turtles produce males in moderate temperatures, while females are produced in warm and chilly conditions.

Fertilisation

Fertilisation is the process of a sperm and an egg joining together. This can happen either inside the female’s body (internal fertilisation) or outside (external fertilisation). The former is demonstrated by humans, whilst the latter is done through frog reproduction.

External Fertilisation

In aquatic conditions where both eggs and sperm are dispersed into the water, external fertilisation typically takes place. Fertilisation occurs after the sperm contacts the egg. The majority of external fertilisation occurs during the spawning phase, when one or more females release their eggs and one or more males discharge sperm simultaneously in the same location.

Environmental cues like water temperature or the amount of daylight may cause the spawning to occur. Almost all fish spawn, along with mollusks (like oysters), squid, echinoderms, and crustaceans (like crabs and shrimp) (such as sea urchins and sea cucumbers). Also, spawning is frogs, corals, mayflies, and mosquitoes.

Internal Fertilisation

Although certain aquatic species also employ this technique, terrestrial animals use internal fertilisation the majority of the time. When mating, the male may directly inject sperm into the female, which may result in internal fertilisation. It can also happen when a man releases sperm into the environment, typically in a protective structure, which a woman picks up and deposits in her reproductive system. After internal fertilisation, children can be created in three different ways. In oviparity, fertilised eggs are placed outside the female’s body where they develop and receive nutrition from the egg yolk.

It occurs in some reptiles, some bony fish, a few cartilaginous fish, a few mammals, all birds, and some amphibians. Most insects and non-avian reptiles deliver leathery eggs, while some turtles and birds produce eggs that have high concentrations of calcium carbonate in the shell. It makes them hard. Chicken eggs are the finest example of a hard shell. The eggs of the egg-laying mammals like echidna and the platypus are leathery.

In ovoviparity, the female keeps the fertilised eggs, and the yolk of the egg provides the embryo with nutrition. The female either deposits the eggs just before they hatch or retains them in her body until they do so. Until they hatch, the eggs are protected through this process. Some sharks, lizards, some snakes (garter snake Thamnophis sirtalis), some vipers, some bony fish (such as the platyfish Xiphophorus maculatus), and some invertebrate creatures also exhibit this trait (Madagascar hissing cockroach Gromphadorhina portentosa).

The young are born alive in viviparity. They are born in various stages of maturity and receive their nutrition from the female. Most mammals, some cartilaginous fish, and a few reptiles exhibit this.

Sexual Reproduction in Animals: Section Summary

Sexual reproduction occurs when the genetic material from two individuals is mixed to produce genetically diverse children, as opposed to asexual reproduction, which occurs when one individual produces genetically identical offspring. Animals can reproduce asexually by parthenogenesis, budding, fission, and fragmentation. Fertilisation can take either inside the body or outside it during sexual reproduction.

A species may have distinct or combined sexes; when combined, the sexes may express themselves at various life cycle stages. Different chromosomal systems or environmental elements like temperature can determine a person’s sex.

A process known as fertilisation begins sexual reproduction when sperm and an egg are combined. This can happen inside or outside of female bodies. Different animals use different methods of fertilisation. Some species release the egg and sperm into the environment. Others keep the egg inside the female body and take the sperm in before expelling the developing embryo with a shell. Still, other species keep the developing child inside the body for the duration of the gestation.

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