Table of Contents
What is Asexual reproduction?
Asexual reproduction is a kind of reproduction that does not involve the union of female and male gametes or sex cells. Reproduction as major characteristics of living organisms involves the process whereby living organisms produce offspring and this process can be carried out sexually or asexually. Asexual reproduction is different from the sexual reproduction common among animals that involves the union of the male and female gametes.
Not all organisms are reproduced by two parents. Some of them like the komodo dragon are reproduced by just one parent which is the mother that reproduces by a type of asexual reproduction called parthenogenesis. Ever wondered how bacteria reproduce as one cant tell if there are female or male bacterium? The fact is bacteria have just one chromosome and don’t have an X or Y chromosome. Hence, they reproduce by the single parent producing a clone that is genetically identical to it using a type of asexual reproduction called binary fission.
In this kind of reproduction, the plant or animal can produce offspring that is a clone of the organism without a mate. Various organisms reproduce via asexual means of reproduction and such organisms include certain plants, some animals, bacteria, fungi, and archaea. There are many types of asexual reproduction that occur in organisms and they include parthenogenesis, apomixis, sporogenesis, fission, vegetative propagation, fragmentation, and budding. All genetic materials in asexual reproduction are passed to the next generation by a parent. Virtually all prokaryotes and certain eukaryotes use various kinds of asexual reproduction to bring forth offspring.
Reproducing asexually can be very rapid and is very advantageous for several organisms. This is because asexual organisms crowd out other organisms that reproduce more slowly. Take the bacteria, for instance, they are overpopulated because they can divide many times in an hour. Approximately 100 bacteria can multiply in few hours to produce millions of bacterial cells under ideal conditions. However, the reproduction of bacteria is kept in check by unfavorable conditions, predators, and limited resources.
Asexual reproduction types
- Binary fission
- Vegetative propagation
One of the asexual reproduction types is binary fission interchangeably called fission. This involves a parent dividing into one or more identical individual cells of equal sizes. The parent single cell divides to reproduce daughter cells and each of these daughter cells has the ability to grow to the original size of the parent cell.
This asexual reproduction type is the primary means of reproduction for prokaryotic organisms. Therefore, fission is common among organisms that are single-celled e.g archaea, bacteria, and protozoans such as amoeba, paramecium, and euglena. Also, fission can be seen in unicellular eukaryotic organisms like some fungi and protists. There are basic fundamental steps of binary fission in prokaryotic organisms which involves:
- The duplication of chromosome
- Segregation of chromosomes
- Formation of a septum in the middle of the cell
- Then, the production of two cells
During the process of binary fission, the parent organisms duplicate their genetic material and divide into two parts in the process of cytokinesis. After cytokinesis, the new organisms each receive a copy of the DNA or genetic material. However, there are different types of binary fission in certain protozoans based on how the cell divides (axis of cell separation). For example, the cells divide along any plane as seen in the binary fission in certain amoeba, making it an irregular type. Whereas, in euglena, the cell division can also be longitudinal and can be a transverse-type, as exemplified in Paramecium. In ceratium, binary fission can be an oblique type.
In organisms like tapeworms and scyphozoan jellyfish, regular transverse fission is referred to as strobilation. This normally gives rise to a chain of products of the fission called a strobilus. In tapeworms, the fission products are the proglottids while in scyphozoan jellyfish it is the ephyrae. The ephyrae as well as the proglottids all mature and separate from the end of the strobilus.
In fragmentation, the parent organism breaks into several fragments that have the ability to later develop into a new organism. This asexual reproduction type can be seen in starfish, sponges, annelid worms, fungi such as lichen and yeasts, some worms, vascular and nonvascular plants, as well as planarians.
A typical example of fragmentation can be seen in a new starfish that develops from a single ray or arm. In addition to the starfish, most lichens reproduce from fragmentation. Lichen is formed from a symbiotic association between a fungus and bacteria or algae. These organisms reproduce through fragmentation, therefore ensuring that the new individuals formed contain both symbionts.
Nevertheless, fragmentation in animals such as sponges, starfish, annelid worms, and planarians is not deliberate as factors such as anthropogenic activities, predation, and environmental factors may cause these animals to split into fragments. From a headless fragment, they develop into completely new organisms.
In budding, organisms are reproduced from an outgrowth (or bud) that develops from an organism. This outgrowth or buds develops into a new individual and even though it is relatively smaller than the parent organism, it is genetically identical to it. This bud or outgrowth may grow attached to the parent organism or may break free (split off) eventually from the parent organism.
Examples of organisms that undergo budding are Brewer’s yeast, coral, hydra, certain bacteria (Caulobacter, Hyphomicrobium, and Stella spp), some acoel flatworms, and echinoderm larvae. In the yeast cell, the small bulb-like projection that comes out from it is called the bud.
Hydra in the process of budding uses regenerative cells for reproduction. As a result of repeated cell division at a specific site in the hydra, a bud develops as an outgrowth into a tiny individual. Then, as these buds fully mature, they detach from the parent body living as new independent individuals. In parasites like the Toxoplasma gondii, internal budding also known as endodyogeny favors them.
Vegetative reproduction also called vegetative propagation is a type of asexual reproduction that reproduces new individuals without the production of seeds or spores. Therefore, it is common in plants, and many plants are reproduced via this means of reproduction. Some plants like the strawberry plants are formed out of stolons or rhizomes, some are reproduced via tubers or bulbs, and some from shoots and suckers that grow along the lateral roots. Whatever way a plant reproduces without seeds or spores is literally a form of vegetative reproduction.
In this type of asexual reproduction, pollination does not occur and a new plant is produced from vegetative parts of the plant like the roots, stems, and leaves. Then, these vegetative parts form their own root system and grow into mature plants. Horticulturists use vegetative propagation to grow plants that are economically important. Furthermore, vegetative reproduction can be classified into two types such as:
- Natural vegetative propagation
- Artificial propagation
Natural Vegetative Propagation
This type of vegetative reproduction occurs naturally in plants without the interference of humans in the production and growth of the new plant. In natural vegetative propagation, the new plants may be reproduced from the stems, roots, and leaves of the parent plant.
Vegetative plant structures such as rhizomes, runners, tubers, and bulbs arise from the plant. Runners, for instance, grow horizontally above the ground and forms buds at the nodes. The tubers of plants are swollen modified roots and they give rise to new plants. Also, few plants have leaves that detach from the parent plant and give rise to new plants. Bulbs have leaves that store food and have these leaves attached to an underground stem. There is an apical bud at the center of the bulb that produces flowers and leaves. Then, the bulb develops shoots from the lateral buds.
Artificial Vegetative Propagation
This type of vegetative reproduction is not natural and is thereby done by humans in the lab or on the fields. Here are some common types of artificial vegetative propagation:
In tissue culture, in order to develop a new plant, the plant cells are cultured in the lab. This method is helpful as it increases the population of rare and endangered species of plants that may not be able to grow under natural conditions.
This method of artificial vegetative propagation involves cutting and planting a part of the plant, specifically a leaf or stem. Sometimes to even induce root development, these cuttings are treated with hormones and the new plant emerges from the adventitious roots that developed from the cutting.
In this artificial propagation, the stem or leaf of another plant is attached to the stem of a plant that is rooted in the ground. Then, over time the tissues of the rooted plant become integrated with the tissue of the graft and the graft develops as a single plant.
In the method of layering, the plant’s stem is bent to the ground and is covered with soil. Then, from the parts of the plant covered with soil, adventitious roots emerge and the attached stem with these developing roots is called the layer.
Any kind of asexual reproduction that doesn’t involve the male gamete is called Agamogenesis. Apomixis and parthenogenesis are such types of reproduction.
Parthenogenesis is a type of asexual reproduction whereby embryos grow and develop without fertilization. It naturally occurs in organisms such as nematodes, certain lizards like Komodo dragons, aphids, rotifers, many plants, and some other invertebrates.
Apomixis too is an asexual reproduction in plants that occurs without fertilization. It occurs in flowering plants where a seed is formed asexually from the maternal tissues of the ovule resulting in the development of an embryo without meiosis and fertilization.
Parthenogenesis is an asexual reproduction that involves offspring growing and developing from the female gamete without being fertilized by the male gamete. So many animals ranging from vertebrates to invertebrates use the process of parthenogenesis to reproduce. Aphids, nematodes, rotifers, etc are all examples of invertebrates that make use of parthenogenesis to bring forth new offsprings.
Some vertebrates like certain birds, lizards, reptiles, sharks, and amphibians can also reproduce via parthenogenesis. Some of them reproduce via facultative parthenogenesis or obligate parthenogenesis. The organisms that reproduce facultatively via parthenogenesis have other means of reproduction and can also reproduce sexually aside from parthenogenesis. Whereas, the obligate parthenogenetic organism can only reproduce via parthenogenesis.
Types of Parthenogenesis
- Apomictic (apomixis) Parthenogenesis
- Automictic (automixis) Parthenogenesis
The process of parthenogenesis are of two types:
In this type of parthenogenesis, the egg cells that are produced by mitosis do not undergo meiosis. The eggs may attain maturity and directly develop into embryos with the new offspring as clones of the parthenogenetic parent.
Since the egg cells in apomixis parthenogenesis do not undergo meiotic division, they become a replicate of the parent cell when it divides. Hence, the offspring are usually a full clone of the mother, producing identical offspring that are similar genetically to the parent. Apomictic parthenogenesis is mostly found in plants.
In this type of parthenogenesis, the egg cells undergo meiosis and the mature egg cell without being fertilized by a sperm cell then develops into an embryo. This form of asexual reproduction is more complicated.
As the egg cell merges with the polar body to produce an embryo, the genes of the mother can shift to produce new alleles and this is why in automixis parthenogenesis the offspring is similar to the mother but is not a full clone. The resulting organism from this type of parthenogenesis gets two X chromosomes from the mother and therefore produces only female offspring. However, in rare cases, fertile males that have only one X chromosome can be produced. The males are fertile because their sperm cells contain only the X chromosome.
This is an asexual reproduction in plants that occurs without fertilization. It occurs in flowering plants where a seed is formed asexually from the maternal tissues of the ovule resulting in the development of an embryo without meiosis and fertilization.
Apogamy and Apospory in non-flowering plants
Apogamy is when the gametophyte of certain plants may reproduce a group of cells that grow to resemble a sporophyte but with a ploidy (the number of chromosomes occurring in the nucleus of a cell) level of a gametophyte. This phenomenon is seen in bryophytes, certain ferns, and lycopods.
Also, the sporophytes of plants like bryophytes, certain ferns, and lycopods are capable of forming gametophyte-looking offsprings but with the ploidy level of the sporophyte in a phenomenon known as apospory.
Agamospermy in flowering plants (angiosperms)
In flowering plants, agamospermy which is the production of seed from unfertilized ovules occurs through many different mechanisms. As a result, there are many different usages of terminology for apomixis in angiosperms. The phenomenon of Agamospermy occurs mainly in two types:
- Gametophytic apomixis
- Sporophytic apomixis
In this type of apomixis, the embryo develops from an unfertilized egg cell in a gametophyte that came from a cell that did not complete meiosis. There are two types of gametophytic apomixis:- apospory and diplospory. In apospory, the megagametophyte forms from the other cell of the nucellus whereas, in diplospory, the megagametophyte forms from a cell of the archesporium.
This type of apomixis is also called nucellar embryony or adventitious embryony where the embryo doesn’t form from a gametophyte but directly from the cells of the nucellus or of an integument.
This asexual reproduction type is known also as spore formation which involves spores. Spores are similar to seeds but are not seeds, they are dormant reproductive cells that serve as dispersal units. They are different from seeds in that they lack the embryo that is produced from the fusion of the female and male gamete.
Spores being thick-walled are highly resistant to several conditions like low humidity and high temperature which are unfavorable conditions. However, in suitable conditions, they germinate and reproduce new offspring. Typical examples of asexual organisms that reproduce via sporogenesis are vascular plants and fungi. Mushroom is an example of a fungus that propagates via spores.
Asexual reproduction examples
- Bacteria undergo binary fission
- Slime molds reproduce via sporogenesis
- Mud worms or blackworms reproduce via fragmentation
- New Mexico whiptail lizards reproduce via parthenogenesis
- Hydras use budding as a means of reproduction
- Sugarcane is grown via vegetative reproduction
Bacteria undergo binary fission
One of the asexual reproduction examples can be seen in bacteria that reproduce via binary fission. In fission, the parent bacterial cell first creates a copy of the DNA molecule to produce two identical clone cells. The DNA duplication is followed by chromosome segregation whereby the DNA is pulled apart towards the opposite poles of the cell dividing. Then, cytokinesis occurs where the cell constricts at the equatorial lane and separates the cellular contents into 2 new cells.
The process of binary fission in bacteria is similar to mitosis in eukaryotic organisms just that there is no spindle apparatus involved in this one. Moreso, the duration of binary fission in bacteria varies between bacterial species. For instance, E.coli can reproduce approximately every 20 minutes at 37 degrees Celcius.
Slime molds reproduce via sporogenesis
One of the examples of asexual reproduction is sporogenesis in slime molds. The plasmodium slime mold in food scarcity and under unfavorable conditions can produce sporangia that contain spores. The sporangia are stalked reproductive fruiting bodies and the cells undergo meiosis at the sporangia’s apical portion. Meiosis results in the haploid spores that are dispersed by the force of the wind.
However, the spore germinates during favorable conditions (like conducive temperature and moisture levels) and releases a haploid cell. Then, the haploid takes part in the sexual phase of the lifecycle of the plasmodium slime mold.
Also, the cellular slime molds in their life cycle undergo sexual and asexual phases. During favorable conditions, they come together and form a pseudoplasmodium because the cells remain distinct. Each of the cells has a nucleus of its own. A real plasmodium in slime molds on the other hand is a single mass of cytoplasm that is not divided by membranes and contains many nuclei.
The cellular slime molds, as well as the plasmodium slime molds both, produce sporangia (fruiting bodies). In the colony, some of the cellular slime molds form the stalk while others form the sporangium that produces the haploid spores and releases them. Each of these spores eventually germinates into individual cells that resemble amoeba.
Mud worms or blackworms reproduce via fragmentation
Another example of asexual reproduction is fragmentation in blackworms. Blackworms like the earthworm possess both male and female sex organs. However, sexual reproduction is not common amongst them as they rather reproduce via fragmentation.
They simply break apart in fragments and each fragment develops into a new worm as it grows a new head and tail. This regrowth from the fragments is known as regeneration and can be seen in some animals like starfish.
New Mexico whiptail lizards reproduce via parthenogenesis
The New Mexico whiptails (Aspidoscelis neomexicanus) are asexual animals that reproduce by parthenogenesis. These lizards are all females and reproduce by doubling the chromosomal number twice in order to have two sets of chromosomes (diploidy).
Initially, they produce 8 copies of each chromosome and give rise to 4 daughter cells after two rounds of cell division. Thus, each daughter cell gets two sets of chromosomes instead of just one set. These lizards still exhibit mating behavior even though they don’t need a male mate. They display a pseudocopulation behavior where a female whiptail mounts another female whiptail which seems to promote ovulation in these organisms.
Unlike other asexual animals that reproduce genetic clones, these lizards still have the ability to produce genetically diverse offspring. This is because they exhibit facultative parthenogenesis, thus can reproduce by another means of reproduction aside from parthenogenesis. The new Mexico whiptails even have a hybridization event that involves the female mating with the males of another species.
Hydras use budding as a means of asexual reproduction
Budding used by hydra is one of the asexual reproduction examples. Hydra reproduces asexually by budding when there is an abundance of food. The buds emerge from the body wall of the hydra and develop into miniature adults. Then, When they mature, they break away from the parent hydra. A new bud can form every two days as far as the hydra is well fed.
However, some hydra reproduces sexually when the conditions are unfavorable and harsh like before winter or in scarcity of food. There are swellings in the body wall during such conditions that develop into either testes or ovaries. However, some Hydra species are hermaphrodites and can produce the testes as well as the ovaries at the same time. e.g Hydra circumcincta and Hydra viridissima.
Free swimming gametes are then released into the water by the testes to fertilize the egg in the ovary of another hydra. When the egg gets fertilized, it secrets a tough outer coating. Once the adult hydra dies as a result of cold or starvation, the eggs fall to the bottom of the water body awaiting favorable conditions. Once they are met with better conditions, they hatch into nymph hydra.
Sugarcane is grown via vegetative reproduction
Sugar cane reproduces via asexual reproduction by using part of the stem called setts or cuttings. The setts of the plant have to contain at least one node for the reproduction of new plants to occur.
The cutting or setts has to have at least a node because it is these nodes that form primary roots when the setts are placed and covered in the ground. Also, the bud primordium on the sett gives rise to the new stem. Ratoon is the name given to the first stalk of sugar cane that comes up each year. In some types of Sugar cane, seeds can be used for reproduction. However, making use of the cuttings of the sugarcane plant is a much more common method.
Asexual reproduction in animals
Reproducing asexually results in genetically identical offspring and requires only one parent animal. The parent organism does not need to find a mate and therefore no combination of genetic information from another organism is involved. Asexual reproduction in animals can increase population rapidly. The disadvantage to reproducing asexually is that the population of the organism is only best adapted for a specific habitat. Thus all members of the population are prone to the same predators and diseases.
- Komodo dragons
- Whiptail lizards
- Python snakes
- Marbled crayfish
- Amazon Molly Fish
- Water Fleas
Asexual reproduction in plants
Several plants reproduce sexually and asexually. When it comes to asexual reproduction in plants, part of the parent plants are used in order for a new plant to emerge. This can be done artificially by several methods and techniques designed by man. The new plant that emerges is usually identical to the parent plant from which the part used was taken. Asexual plants thrive well in stable environments compared to plants produced sexually.
Types of asexual reproduction in plants
- Natural methods of asexual reproduction
- Artificial method of asexual reproduction
The natural methods of asexual reproduction comprise of ways plants take on to propagate themselves. It involves asexual reproduction occurring naturally in plants without the interference of humans in the production and growth of the new plant.
Some plants grow continuously from buds on their stem surface e.g onion, ginger, dahlia, and gladioli, etc. In some plants, the adventitious roots or runners naturally reproduce new plants like in the sweet potato. The new plants may be reproduced naturally from the stems, roots, and leaves of the parent plant.
Vegetative plant structures such as rhizomes, runners, tubers, and bulbs arise from the plant. Runners, for instance, grow horizontally above the ground and forms buds at the nodes. Tubers are swollen modified roots and they give rise to new plants. Also, few plants have leaves that detach from the parent plant and give rise to new plants.
Bulbs have leaves that store food and have these leaves attached to an underground stem. There is an apical bud at the center of the bulb that produces flowers and leaves. The bulb then develops shoots from the lateral buds.
The artificial methods of asexual reproduction in plants don’t occur naturally. This involves methods of reproduction that are influenced by humans in the lab or on the fields. Here are some common types of artificial vegetative propagation:
- Tissue culture
This is an artificial method of asexual propagation in plants where the stem or leaf of another plant is attached to the stem of a plant that is rooted in the ground. Over time, the tissues of the rooted plant become integrated with the tissue of the graft and the graft develops as a single plant. The grafted stem is called the scion while the root is referred to as the stock.
This method of artificial asexual reproduction involves cutting and planting a part of the plant, specifically a leaf or stem. Sometimes to even induce root development, these cuttings are treated with hormones and the new plant emerges from the adventitious roots that develop from the cutting.
This is an artificial method whereby a portion of the stem is bent and buried in the soil to form a new plant. In the method of layering, the plant’s stem is bent to the ground and is covered with soil for adventitious roots to emerge. The attached stem with these developing roots is called the layer. In this method, it is preferable to use young stems that can easily bend without any injury. Plants like jasmine and paper flowers (bougainvillea) are grown using this method.
Micropropagation is an artificial method of reproduction where new plants are developed from culturing plant cells in the lab. This method is also known as plant tissue culture and is helpful because it increases the population of rare and endangered species of plants are may not be able to grow under natural conditions.
Examples of Asexual Plants
- Garlic, gladiolus, and crocuses (Crocus) use corm to reproduce asexually.
- Bulbs (scally bulbs) are used in lilies for asexual reproduction.
- The tunicate bulb is used in daffodils for asexual propagation.
- Adventitious roots can give rise to new plants like in the case of ivy.
- Some plants like the parsnip can propagate from the taproot.
- Potatoes and dahlia are stem tubers that reproduce by using underground tubers.
- The rhizome is an organ of asexual reproduction as its growing tips can separate as new plants such as in iris, ginger, nettles, and couch grass.
- The stolon also known as a runner are prostrate aerial stems that are used for asexual reproduction in plants like strawberry, some ferns, and numerous grasses.
- Adventitious buds can form on damaged stems, old roots, or roots that are near the surface of the ground. These buds can then develop into stems and leaves.
- Some plants are propagated asexually via their suckers such as in dandelion, elm, Rosa, and rubus.
- The leaves of plants like Bryophyllum and kalanchoe have small buds. The buds grow on the margins of the leaves and detach from the plant to grow into new independent plants. Also, new independent plants may grow when the leaves touch the soil.
- The underground bulbs of plants divide into more bulbs to reproduce new plants like onions, narcissus, hyacinth, and tulips.
- Asexual reproduction in some flowering plants involves the production of seeds without fertilization. This reproduction type is called apomixis and seed is formed asexually from the maternal tissues of the ovule resulting in the development of an embryo without meiosis and fertilization. This is common in plants like bryophytes, certain ferns, and lycopods.
These plants propagate themselves by using an asexual means of reproduction. Asexual reproduction in plants doesn’t need the usual sexual processes of flower production, sorting for means of seed dispersal or attracting pollinators.
Asexual reproduction in humans
Not only do plants and animals have means of asexual reproduction, but humans also have. It is known that humans reproduce sexually as the most advanced and evolved class of the animal kingdom. However, the means of reproduction in humans that is close enough to asexual reproduction is seen in the case of in-vitro fertilization.
Asexual reproduction in humans is done without the immediate use of the fertilized female sex cells by the male sex cell. It is carried out by fusing a few parts of the sperm cell, embryo, egg, or natural genes in order to create a new human fetus. Then, depending on the medical procedures, this fetus undergoes further maturation and development. This asexual means of reproduction is usually an option in the case of infertility and is carried out using assisted reproductive treatment like IVF (Invitro fertilization).
Furthermore, there is a natural asexual reproduction known as monozygotic twinning that occurs in the woman’s body. It has been used in the IVF cycles for decades and is like a kind of human cloning. Moreso, the cloning by somatic cell nuclear transfer is another type of asexual reproduction in humans that is done artificially as part of IVF.
Additionally, in the field of medicine, there is a breakthrough in the latest advancement of asexual reproduction known as 3-parent-embryo. This involves the utilization of several techniques like mitochondrial transfer which is another type of cloning. The concept surrounding this means of asexual reproduction in humans is that 3 parents can be used to produce a single embryo. The mitochondria found in the female egg, in case of any defect are replaced by the mitochondria from the third party.
Advantages of asexual reproduction
- Asexual reproduction does not require a mating partner.
- The process of reproducing asexually is rapid and relatively more straightforward compared to sexual reproduction.
- Asexual organisms can reproduce many offsprings of their own kind without mating.
- Through asexual reproduction, a large number of organisms can be produced in very little time.
- In this kind of reproduction, positive genetic influences can be easily passed on to successive generations.
- Asexual reproduction takes less energy and time.
- It can occur in several environments and asexual organisms have more advantages in colonizing a habitat faster than sexual organisms.
- Plants that are reproduced asexually reach maturity faster and are sturdier than seedlings from sexual reproduction.
Disadvantages of asexual reproduction
- Lack of diversity
- Difficulty adapting to changes in the environment
Lack of diversity
Asexual reproduction can cause a lack of diversity because the offsprings produced are genetically identical to the parent which makes them more prone to the same nutrient deficiencies and diseases as the parent.
The diversity of these organisms are usually limited because only one organism is involved. Asexual organisms cloning themselves is eventually a disadvantage in the long run because it leads to low genetic variation.
This is not so for organisms that reproduce sexually because, during meiosis, they incorporate recombination and segregation. Also, in sexual organisms, there is a fusion of sex cells with unique genetic materials. Asexuals skip meiotic events and do not go through these processes and this could mean less genetic diversity.
Difficulty adapting to changes in the environment
Asexual organisms are unable to adapt to the changing environment as a single abiotic change can eliminate the entire species. In asexuals, the clone inherits the same genetic material from the lone parent. They are both similarly susceptible to a sudden disturbance in their environment because they have the same characteristics and genes. For instance, in a case of a virulent disease, they both may lack the genes that could be resistant to the disease. Hence, they are at risk of being eliminated from the environment.
Sexual reproduction gives rise to species that possess genes that make them a better fit for a new environment and this factor is very crucial. Sexual organisms achieve higher diversity through gamete fusion, crossing over, and independent assortment. Whereas, purely asexual parents can get new genes through mutation.
Video explaining asexual reproduction