Parthenogenesis – Examples, Types, and Significance

Parthenogenesis is a reproductive process in which a female can produce an embryo without prior fertilization of an egg with sperm. Some of the parthenogenesis examples include invertebrates such as ants, wasps, aphids, bees, etc. Parthenogenesis in plants is less common than in animals.

It can be natural in some species, for example, in some algae, nematodes, etc., or it can be induced in some species for example, in some fishes, amphibians, and mice using artificial means such as hormonal treatment, temperature manipulation, etc. In this article, we will study parthenogenesis meaning, mechanism, types, significance, and variations of Parthenogenesis.

What is Parthenogenesis?

Parthenogenesis Definition: Parthenogenesis is the process of reproduction without fertilization.

The word parthenogenesis is made up of two Greek words- “parthenos” meaning virgin and “genesis” meaning creation. Hence sometimes it is referred to as a “virgin creation”. The majority of animals need to breed to reproduce but some animals can produce offspring without mating and it is referred to as parthenogenesis.

This is why parthenogenesis can be defined as a process of natural asexual reproduction in which an embryo grows and develops from an unfertilized egg cell. The egg produced parthenogenetically can have either a haploid or a single set of dissimilar chromosomes or a diploid or paired set of chromosomes. Parthenogenesis may be rarely observed in higher vertebrates.

Examples of Parthenogenesis

Examples of parthenogenic organisms: are ants, mites, the zebra shark, water fleas, wasps, some bees, and other insects, etc.

Mechanism of Parthenogenesis

Parthenogenesis is a type of asexual reproduction. However, it can be considered more accurately as incomplete sexual reproduction because the offspring produced are developed from the gametes, and gametes are reproductive cells formed as a result of reduction division i.e. meiosis. It can occur mainly in the following two ways:

Automixis

It is a process in which reproductive cells are produced by meiosis. Due to meiotic division during egg cell development (oogenesis), the resulting daughter cells are divided unequally which results in the formation of one large egg cell called oocyte and smaller cells called polar bodies. The egg cell is haploid and becomes diploid by duplicating its chromosome or by fusing with the polar body.

The fusion of haploid egg cells with a polar body is known as automixis. The resulting offspring are produced by meiosis and, hence are not clones of the parent cell. This mechanism is mostly observed in sharks.

Apomixis

Apomixis is a process in which reproductive cells do not undergo meiosis and are multiplied by mitosis. Hence, the resulting offspring are identical copies/clones of their parents and are developed into diploid offspring. It is also known as apomictic parthenogenesis. This mechanism is most common in plants and in some aphids.

Parthenogenesis Types

Based on the ways by which parthenogenesis occurs, it has been classified into the following two types:

Natural Parthenogenesis

In some organisms or animals, when parthenogenesis occurs naturally, regularly, and continuously in their life cycles, then such parthenogenesis is known as natural parthenogenesis. There are two types of natural parthenogenesis:

• Complete Parthenogenesis: Some insects have no males and no sexual phase in their life cycles and to breed they solely depend upon self-reproduction. Such type of parthenogenesis is known as complete parthenogenesis or obligatory parthenogenesis. For example, Bdelloid Rotifers, Monogonont Rotifers, Caucasian Rock lizards, some species of earthworms, salamanders, etc. have this trait.
• Incomplete Parthenogenesis: In some insects during their life cycle they have alternate generations of sexual generation and parthenogenetic generation. In such cases, the diploid egg produces females whereas the unfertilized egg forms males. This type of parthenogenesis is known as incomplete or cyclic or partial parthenogenesis. Examples: honey bees, wasps, aphids, ticks, mites, etc.

Artificial Parthenogenesis

Under certain controlled conditions, the eggs, which always develop into young ones through fertilization, can develop into young individuals parthenogenetically. Such parthenogenesis is called artificial parthenogenesis. The artificial parthenogenesis can be induced by using various physical means and chemical means.

The physical means that induce parthenogenesis are:

• Temperature change may induce parthenogenesis in eggs. For example, if an egg is transferred from a place of 30°C to 0°- 10°C, parthenogenesis is triggered.
• Ultraviolet radiation can also trigger parthenogenesis.
• Electric shock is also capable of inducing parthenogenesis.
• Eggs when pricked with a needle, can develop parthenogenetically.

The chemical means that induce parthenogenesis. It has been found the following chemicals can induce parthenogenesis in organisms:

• Chloroform
• Urea and sugar
• Various chlorides, such as Ca⁺⁺, Mg⁺⁺ ,K⁺, Na⁺, etc.
• Strychnine
• Fat solvents
• Acids

Significance of Parthenogenesis

Parthenogenesis is common in lower plants and invertebrate animals and rarely found in higher vertebrates. Parthenogenesis is an interesting phenomenon among different reproduction processes. The following are the significance of parthenogenesis:

• Some animal species such as bees or a few species of fish do not have sex chromosomes. In this situation, parthenogenesis became the most important component of their reproduction.
• Parthenogenesis can be natural or it may be done artificially. Hence, it helps to ensure the right balance between male and female offspring in the population.
• It facilitates fast reproduction and population growth without involving fertilization.
• Parthenogenetically produced organisms have less variation or practically no variation. Such organisms thrive well because they are already well adapted to the specific environment.
• Parthenogenesis is a type of adaptive technique hence, it helps to protect the endangered species. Because it allows organisms to reproduce in improper environmental conditions.

Parthenogenesis in Animals

In animals, parthenogenesis occurs spontaneously or as a natural form of asexual reproduction. It is very common in the animal kingdom. Animals can have either apomictic parthenogenesis or automictic parthenogenesis. Animals that are produced by apomictic parthenogenesis are usually full clones of their mothers. While animals produced via automictic parthenogenesis are not clones of their mothers.

Examples of parthenogenesis in animals are birds, snakes, sharks, lizards, fish reptiles, etc. Birds, snakes, sharks, and lizards have strict parthenogenesis whereas, fish, and reptiles have incomplete parthenogenesis. Some species of sharks, for example, blacktip & hammerhead sharks and also Komodo Dragon usually reproduce sexually but occasionally they reproduce asexually by parthenogenesis.

Parthenogenesis in Insects

Parthenogenesis is found in several species of insects as well. The Indian or Laboratory stick insect is the most common and well-known example of parthenogenesis in insects. Some other examples of insects that show parthenogenesis are mites, wasps, water fleas, ants, etc. Some insects exhibit obligate parthenogenesis (reproduce only by parthenogenesis) and some exhibit facultative parthenogenesis (switch between sexual reproduction and parthenogenesis). Parthernogenesis in honey bee is also a common example of parthenogenesis in insects.

Parthenogenesis in Plants

Parthenogenesis is not limited to animals & insects only. It can also occur naturally in plants. Plants such as algae, mosses, some ferns, and rarely higher flowering plants also possess this trait. It is usually found in plants as a combination of endospore formation and apomeiosis. Together it is referred to as clonal seed production. Different mechanisms, such as apospory, diplospory, apogamy, etc, are involved in plant parthenogenesis where they produce either true or partial clones of the maternal genome.

What Variations are Seen in Parthenogenesis?

Several variations have been observed in parthenogenesis. In some species such as in aphids and water fleas, there is an alternation of generations of offspring produced from fertilized eggs and generations of offspring produced from unfertilized eggs. Such variation in parthenogenesis is called heterogony or cyclic parthenogenesis. There is another type of variation known as pseudogamy or sperm-dependent parthenogenesis. In this type of variation, the sperm is utilized only to stimulate the initial development of the egg, the genetic material of sperm is not used. This type of variation has been seen in the life cycle of a few mites, salamanders, flatworms, etc.

Conclusion – Parthenogenesis

Parthenogenesis is a process of reproduction of organisms without fertilization. Usually, reproduction requires mating of males and females but parthenogenesis is a form of reproduction that does not require males. However, most organisms that exhibit parthenogenesis also utilize sexual behavior or sexual reproduction. Lots of diversity is found in nature for the adaptation of organisms and parthenogenesis is a part of that wide diversity. It helps in the continuation of the lineage of organisms. It can occur naturally or can be triggered artificially both in animals and plants.

FAQs on Parthenogenesis

Can Parthenogenesis Occurs in Humans?

Parthenogenesis is not possible in humans. Parthenogenesis in humans depends on several factors- oocyte, meiosis, genetic imprinting, etc. and if it occurs it will produce tumors such as ovarian teratoma.

Why Parthenogenesis is also called’ Virgin Birth’?

Parthenogenesis is also called ‘virgin birth’ because it involves unfertilized eggs for the production of individuals. It is derived from two Greek words ‘parthenos’ means virgin and ‘genesis’ which means creation.

Does Parthenogenesis produce only Female Offspring?

Parthenogenesis can produce both male and female offspring. In the case of the fertilized eggs female offspring are produced and if eggs remain unfertilized then male offspring are produced.

Can Females Reproduce without Males?

Yes, it is possible and the process by which females reproduce without males is known as parthenogenesis. It is mostly observed in lower plants and invertebrates.

What is the Difference Between Parthenogenesis and Parthenocarpy?

The major difference between parthenogenesis and parthenocarpy is that in parthenogenesis an individual is produced from an unfertilized egg and it occurs in animals and lower plants. Whereas, parthenocarpy leads to the development of fruits without seeds.

What is Parthenogenesis Asexual Reproduction?

Parthenogenesis is an asexual reproductive process where offspring develop from unfertilized eggs, commonly observed in certain insects, reptiles, fish, and occasionally in plants.

What is Parthenogenesis Meaning?

Parthenogenesis refers to the reproduction process in which offspring develop from unfertilized eggs, observed in various organisms including insects, reptiles, fish, and occasionally in plants.

Is Parthenogenesis in Humans Possible?

No, parthogenesis is not possible in humans naturally and is currently considered biologically impossible without external manipulation of genetic material.

What is Parthogenesis in Honey Bees?

Parthenogenesis in honey bees refers to the development of drones (male bees) from unfertilized eggs laid by the queen bee. This process allows for the production of male offspring without the need for fertilization by a male drone.