For other uses, see Reproduction (disambiguation).
Reproduction (or procreation or breeding) is the biological process by which new individual organisms – "offspring" – are produced from their "parents". Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction. There are two forms of reproduction: asexual and sexual.
In asexual reproduction, an organism can reproduce without the involvement of another organism. Asexual reproduction is not limited to single-celled organisms. The cloning of an organism is a form of asexual reproduction. By asexual reproduction, an organism creates a genetically similar or identical copy of itself. The evolution of sexual reproduction is a major puzzle for biologists. The two-fold cost of sexual reproduction is that only 50% of organisms reproduce and organisms only pass on 50% of their genes.
Sexual reproduction typically requires the sexual interaction of two specialized organisms, called gametes, which contain half the number of chromosomes of normal cells and are created by meiosis, with typically a male fertilizing a female of the same species to create a fertilized zygote. This produces offspring organisms whose genetic characteristics are derived from those of the two parental organisms.
Main article: Asexual reproduction
Asexual reproduction is a process by which organisms create genetically similar or identical copies of themselves without the contribution of genetic material from another organism. Bacteria divide asexually via binary fission; viruses take control of host cells to produce more viruses; Hydras (invertebrates of the orderHydroidea) and yeasts are able to reproduce by budding. These organisms often do not possess different sexes, and they are capable of "splitting" themselves into two or more copies of themselves. Most plants have the ability to reproduce asexually and the ant species Mycocepurus smithii is thought to reproduce entirely by asexual means.
Some species that are capable of reproducing asexually, like hydra, yeast (See Mating of yeasts) and jellyfish, may also reproduce sexually. For instance, most plants are capable of vegetative reproduction—reproduction without seeds or spores—but can also reproduce sexually. Likewise, bacteria may exchange genetic information by conjugation.
Other ways of asexual reproduction include parthenogenesis, fragmentation and spore formation that involves only mitosis. Parthenogenesis is the growth and development of embryo or seed without fertilization by a male. Parthenogenesis occurs naturally in some species, including lower plants (where it is called apomixis), invertebrates (e.g. water fleas, aphids, some bees and parasitic wasps), and vertebrates (e.g. some reptiles,fish, and, very rarely, birds and sharks). It is sometimes also used to describe reproduction modes in hermaphroditic species which can self-fertilize.
Main article: Sexual reproduction
See also: Human reproduction
Sexual reproduction is a biological process that creates a new organism by combining the genetic material of two organisms in a process that starts with meiosis, a specialized type of cell division. Each of two parent organisms contributes half of the offspring's genetic makeup by creating haploidgametes. Most organisms form two different types of gametes. In these anisogamous species, the two sexes are referred to as male (producing sperm or microspores) and female (producing ova or megaspores). In isogamous species, the gametes are similar or identical in form (isogametes), but may have separable properties and then may be given other different names (see isogamy). For example, in the green alga, Chlamydomonas reinhardtii, there are so-called "plus" and "minus" gametes. A few types of organisms, such as many fungi and the ciliateParamecium aurelia, have more than two "sexes", called syngens. Most animals (including humans) and plants reproduce sexually. Sexually reproducing organisms have different sets of genes for every trait (called alleles). Offspring inherit one allele for each trait from each parent. Thus, offspring have a combination of the parents' genes. It is believed that "the masking of deleterious alleles favors the evolution of a dominant diploid phase in organisms that alternate between haploid and diploid phases" where recombination occurs freely.
Bryophytes reproduce sexually, but the larger and commonly-seen organisms are haploid and produce gametes. The gametes fuse to form a zygote which develops into a sporangium, which in turn produces haploid spores. The diploid stage is relatively small and short-lived compared to the haploid stage, i.e. haploid dominance. The advantage of diploidy, heterosis, only exists in the diploid life generation. Bryophytes retain sexual reproduction despite the fact that the haploid stage does not benefit from heterosis. This may be an indication that the sexual reproduction has advantages other than heterosis, such as genetic recombination between members of the species, allowing the expression of a wider range of traits and thus making the population more able to survive environmental variation.
Main article: Allogamy
Allogamy is the fertilization of the combination of gametes from two parents, generally the ovum from one individual with the spermatozoa of another. (In isogamous species, the two gametes will not be defined as either sperm or ovum.)
Main article: Autogamy
Self-fertilization, also known as autogamy, occurs in hermaphroditic organisms where the two gametes fused in fertilization come from the same individual, e.g., many vascular plants, some foraminiferans, some ciliates. The term "autogamy" is sometimes substituted for autogamous pollination (not necessarily leading to successful fertilization) and describes self-pollination within the same flower, distinguished from geitonogamous pollination, transfer of pollen to a different flower on the same flowering plant, or within a single monoeciousGymnosperm plant.
Mitosis and meiosis
Mitosis and meiosis are types of cell division. Mitosis occurs in somatic cells, while meiosis occurs in gametes.
Mitosis The resultant number of cells in mitosis is twice the number of original cells. The number of chromosomes in the offspring cells is the same as that of the parent cell.
Meiosis The resultant number of cells is four times the number of original cells. This results in cells with half the number of chromosomes present in the parent cell. A diploid cell duplicates itself, then undergoes two divisions (tetraploid to diploid to haploid), in the process forming four haploid cells. This process occurs in two phases, meiosis I and meiosis II.
In recent decades, developmental biologists have been researching and developing techniques to facilitate same-sex reproduction. The obvious approaches, subject to a growing amount of activity, are female sperm and male eggs, with female sperm closer to being a reality for humans, given that Japanese scientists have already created female sperm for chickens. "However, the ratio of produced W chromosome-bearing (W-bearing) spermatozoa fell substantially below expectations. It is therefore concluded that most of the W-bearing PGC could not differentiate into spermatozoa because of restricted spermatogenesis." In 2004, by altering the function of a few genes involved with imprinting, other Japanese scientists combined two mouse eggs to produce daughter mice.
Further information: Modes of reproduction
There are a wide range of reproductive strategies employed by different species. Some animals, such as the human and northern gannet, do not reach sexual maturity for many years after birth and even then produce few offspring. Others reproduce quickly; but, under normal circumstances, most offspring do not survive to adulthood. For example, a rabbit (mature after 8 months) can produce 10–30 offspring per year, and a fruit fly (mature after 10–14 days) can produce up to 900 offspring per year. These two main strategies are known as K-selection (few offspring) and r-selection (many offspring). Which strategy is favoured by evolution depends on a variety of circumstances. Animals with few offspring can devote more resources to the nurturing and protection of each individual offspring, thus reducing the need for many offspring. On the other hand, animals with many offspring may devote fewer resources to each individual offspring; for these types of animals it is common for many offspring to die soon after birth, but enough individuals typically survive to maintain the population. Some organisms such as honey bees and fruit flies retain sperm in a process called sperm storage thereby increasing the duration of their fertility.
Main article: Semelparity and iteroparity
- Polycyclic animals reproduce intermittently throughout their lives.
- Semelparous organisms reproduce only once in their lifetime, such as annual plants (including all grain crops), and certain species of salmon, spider, bamboo and century plant. Often, they die shortly after reproduction. This is often associated with r-strategists.
- Iteroparous organisms produce offspring in successive (e.g. annual or seasonal) cycles, such as perennial plants. Iteroparous animals survive over multiple seasons (or periodic condition changes). This is more associated with K-strategists.
Asexual vs. sexual reproduction
Organisms that reproduce through asexual reproduction tend to grow in number exponentially. However, because they rely on mutation for variations in their DNA, all members of the species have similar vulnerabilities. Organisms that reproduce sexually yield a smaller number of offspring, but the large amount of variation in their genes makes them less susceptible to disease.
Many organisms can reproduce sexually as well as asexually. Aphids, slime molds, sea anemones, some species of starfish (by fragmentation), and many plants are examples. When environmental factors are favorable, asexual reproduction is employed to exploit suitable conditions for survival such as an abundant food supply, adequate shelter, favorable climate, disease, optimum pH or a proper mix of other lifestyle requirements. Populations of these organisms increase exponentially via asexual reproductive strategies to take full advantage of the rich supply resources.
When food sources have been depleted, the climate becomes hostile, or individual survival is jeopardized by some other adverse change in living conditions, these organisms switch to sexual forms of reproduction. Sexual reproduction ensures a mixing of the gene pool of the species. The variations found in offspring of sexual reproduction allow some individuals to be better suited for survival and provide a mechanism for selective adaptation to occur. The meiosis stage of the sexual cycle also allows especially effective repair of DNA damages (see Meiosis and Bernstein et al.). In addition, sexual reproduction usually results in the formation of a life stage that is able to endure the conditions that threaten the offspring of an asexual parent. Thus, seeds, spores, eggs, pupae, cysts or other "over-wintering" stages of sexual reproduction ensure the survival during unfavorable times and the organism can "wait out" adverse situations until a swing back to suitability occurs.
The existence of life without reproduction is the subject of some speculation. The biological study of how the origin of life produced reproducing organisms from non-reproducing elements is called abiogenesis. Whether or not there were several independent abiogenetic events, biologists believe that the last universal ancestor to all present life on Earth lived about 3.5 billion years ago.
Scientists have speculated about the possibility of creating life non-reproductively in the laboratory. Several scientists have succeeded in producing simple viruses from entirely non-living materials. However, viruses are often regarded as not alive. Being nothing more than a bit of RNA or DNA in a protein capsule, they have no metabolism and can only replicate with the assistance of a hijacked cell's metabolic machinery.
The production of a truly living organism (e.g. a simple bacterium) with no ancestors would be a much more complex task, but may well be possible to some degree according to current biological knowledge. A synthetic genome has been transferred into an existing bacterium where it replaced the native DNA, resulting in the artificial production of a new M. mycoides organism.
There is some debate within the scientific community over whether this cell can be considered completely synthetic on the grounds that the chemically synthesized genome was an almost 1:1 copy of a naturally occurring genome and, the recipient cell was a naturally occurring bacterium. The Craig Venter Institute maintains the term "synthetic bacterial cell" but they also clarify "...we do not consider this to be "creating life from scratch" but rather we are creating new life out of already existing life using synthetic DNA". Venter plans to patent his experimental cells, stating that "they are pretty clearly human inventions". Its creators suggests that building 'synthetic life' would allow researchers to learn about life by building it, rather than by tearing it apart. They also propose to stretch the boundaries between life and machines until the two overlap to yield "truly programmable organisms". Researchers involved stated that the creation of "true synthetic biochemical life" is relatively close in reach with current technology and cheap compared to the effort needed to place man on the Moon.
Sexual reproduction has many drawbacks, since it requires far more energy than asexual reproduction and diverts the organisms from other pursuits, and there is some argument about why so many species use it. George C. Williams used lottery tickets as an analogy in one explanation for the widespread use of sexual reproduction. He argued that asexual reproduction, which produces little or no genetic variety in offspring, was like buying many tickets that all have the same number, limiting the chance of "winning" - that is, producing surviving offspring. Sexual reproduction, he argued, was like purchasing fewer tickets but with a greater variety of numbers and therefore a greater chance of success. The point of this analogy is that since asexual reproduction does not produce genetic variations, there is little ability to quickly adapt to a changing environment. The lottery principle is less accepted these days because of evidence that asexual reproduction is more prevalent in unstable environments, the opposite of what it predicts.
- Tobler, M. & Schlupp, I. (2005) Parasites in sexual and asexual mollies (Poecilia, Poeciliidae, Teleostei): a case for the Red Queen? Biol. Lett. 1 (2): 166-168.
- Zimmer, Carl. Parasite Rex: Inside the Bizarre World of Nature's Most Dangerous Creatures, New York: Touchstone, 2001.
- "Allogamy, cross-fertilization, cross-pollination, hybridization". GardenWeb Glossary of Botanical Terms (2.1 ed.). 2002.
- "Allogamy". Stedman's Online Medical Dictionary (27 ed.). 2004.
- ^Ridley M (2004) Evolution, 3rd edition. Blackwell Publishing, p. 314.
- ^John Maynard SmithThe Evolution of Sex 1978.
- ^Halliday, Tim R.; Adler, Kraig (eds.) (1986). Reptiles & Amphibians. Torstar Books. p. 101. ISBN 0-920269-81-8.
- ^Savage, Thomas F. (September 12, 2005). "A Guide to the Recognition of Parthenogenesis in Incubated Turkey Eggs". Oregon State University. Archived from the original on November 15, 2006. Retrieved 2006-10-11.
- ^"Female Sharks Can Reproduce Alone, Researchers Find", Washington Post, Wednesday, May 23, 2007; Page A02
- ^T. M. Sonneborn. Mating Types in Paramecium Aurelia: Diverse Conditions for Mating in Different Stocks; Occurrence, Number and Interrelations of the Types. Proceedings of the American Philosophical Society, Vol. 79, No. 3 (Sep. 30, 1938), pp. 411-434. American Philosophical Society. JSTOR 984858.
- ^S. P. Otto and D. B. Goldstein. "Recombination and the Evolution of Diploidy". Genetics. Vol 131 (1992): 745-751.
- ^Bernstein H, Hopf FA, Michod RE. (1987) The molecular basis of the evolution of sex. Adv Genet.24:323-370. Review. PMID 3324702
- ^Eckert, C.G. (2000). "Contributions of autogamy and geitonogamy to self-fertilization in a mass-flowering, clonal plant". Ecology. 81 (2): 532–542. doi:10.1890/0012-9658(2000)081[0532:coaagt]2.0.co;2.
- ^"Timeline of same-sex procreation scientific developments". samesexprocreation.com.
- ^"Differentiation of female chicken primordial germ cells into spermatozoa in male gonads". 39 (3). June 1997: 267–71. doi:10.1046/j.1440-169X.1997.t01-2-00002.x. PMID 9227893.
- ^"Japanese scientists produce mice without using sperm". Washington Post. Sarasota Herald-Tribune. April 22, 2004.
- ^Bernstein H., Bernstein C. and Michod R.E. (2011). Meiosis as an Evolutionary Adaptation for DNA Repair. Chapter 19: 357-382 in DNA Repair, Inna Kruman (Ed.), InTech (publisher) ISBN 978-953-307-697-3. Available online from intechopen.com
- ^Chemical synthesis of poliovirus cDNA: generation of infectious virus in the absence of natural template
Scientists Create Artificial Virus
- ^Gibson, D.; Glass, J.; Lartigue, C.; Noskov, V.; Chuang, R.; Algire, M.; Benders, G.; Montague, M.; Ma, L.; Moodie, M. M.; Merryman, C.; Vashee, S.; Krishnakumar, R.; Assad-Garcia, N.; Andrews-Pfannkoch, C.; Denisova, E. A.; Young, L.; Qi, Z. -Q.; Segall-Shapiro, T. H.; Calvey, C. H.; Parmar, P. P.; Hutchison Ca, C. A.; Smith, H. O.; Venter, J. C. (2010). "Creation of a Bacterial Cell Controlled by a Chemically Synthesized Genome". Science. 329 (5987): 52–56. Bibcode:2010Sci...329...52G. doi:10.1126/science.1190719. PMID 20488990.
- ^ abRobert Lee Hotz (May 21, 2010). "Scientists Create First Synthetic Cell". The Wall Street Journal. Retrieved April 13, 2012.
- ^Craig Venter Institute. "FAQ". Retrieved 2011-04-24.
- ^W. Wayte Gibbs (May 2004). "Synthetic Life". Scientific American.
- ^"NOVA: Artificial life". Retrieved 2007-01-19.
- ^Williams G C. 1975. Sex and Evolution. Princeton (NJ): Princeton University Press.
Asexual Reproduction Definition
Asexual reproduction occurs when an organism makes more of itself without exchanging genetic information with another organism through sex.
In sexually reproducing organisms, the genomes of two parents are combined to create offspring with unique genetic profiles. This is beneficial to the population because genetically diverse populations have a higher chance of withstanding survival challenges such as disease and environmental changes.
Asexually reproducing organisms can suffer a dangerous lack of diversity – but they can also reproduce faster than sexually reproducing organisms, and a single individual can found a new population without the need for a mate.
Some organisms that practice asexual reproduction can exchange genetic information to promote diversity using forms of horizontal gene transfer such as bacteria who use plasmids to pass around small bits of DNA. However this method results in fewer unique genotypes than sexual reproduction.
Some species of plants, animals, and fungi are capable of both sexual and asexual reproduction, depending on the demands of the environment.
Asexual reproduction is practiced by most single-celled organisms including bacteria, archaebacteria, and protists. It is also practiced by some plants, animals, and fungi.
Evolution and animal life
Advantages of Asexual Reproduction
Important advantages of asexual reproduction include:
1. Rapid population growth. This is especially useful for species whose survival strategy is to reproduce very fast.
Many species of bacteria, for example, can completely rebuild a population from just a single mutant individual in a matter of days if most members are wiped out by a virus.
2. No mate is needed to found a new population.
This is useful for species whose members may find themselves isolated, such as fungi that grow from wind-blown spores, plants that rely on pollinators for sexual reproduction, and animals inhabiting environments with low population density.
3. Lower resource investment. Asexual reproduction, which can often be accomplished just by having part of the parent organism split off and take on a life of its own, takes fewer resources than nurturing a new baby organism.
Many plants and sea creatures, for example, can simply cut a part of themselves off from the parent organism and have that part survive on its own.
Only offspring that are genetically identical to the parent can be produced in this way: nurturing the creation of a new organism whose tissue is different from the parents’ tissue takes more time, energy, and resources.
This ability to simply split in two is one reason why asexual reproduction is faster than sexual reproduction.
Disadvantages of Asexual Reproduction
The biggest disadvantage of asexual reproduction is lack of diversity. Because members of an asexually reproducing population are genetically identical except for rare mutants, they are all susceptible to the same diseases, nutrition deficits, and other types of environmental hardships.
The Irish Potato Famine was one example of the down side of asexual reproduction: Ireland’s potatoes, which had mainly reproduced through asexual reproduction, were all vulnerable when a potato-killing plague swept the island. As a result, almost all crops failed, and many people starved.
The near-extinction of the Gros-Michel banana is another example – one of two major cultivars of bananas, it became impossible to grow commercially in the 20th century after the emergence of a disease to which it was genetically vulnerable.
On the other hand, many species of bacteria actually take advantage of their high mutation rate to create some genetic diversity while using asexual reproduction to grow their colonies very rapidly. Bacteria have a higher rate of errors in copying genetic sequences, which sometimes leads to the creation of useful new traits even in the absence of sexual reproduction.
Types of Asexual Reproduction
There are many different ways to reproduce asexually. These include:
1. Binary fission. This method, in which a cell simply copies its DNA and then splits in two, giving a copy of its DNA to each “daughter cell,” is used by bacteria and archaebacteria.
2. Budding. Some organisms split off a small part of themselves to grow into a new organism. This is practiced by many plants and sea creatures, and some single-celled eukaryotes such as yeast.
3. Vegetative propagation. Much like budding, this process involves a plant growing a new shoot which is capable of becoming a whole new organism. Strawberries are an example of plants that reproduce using “runners,” which grow outward from a parent plant and later become separate, independent plants.
4. Sporogenesis. Sporogenesis is the production of reproductive cells, called spores, which can grow into a new organism.
Spores often use similar strategies to those of seeds. But unlike seeds, spores can be created without fertilization by a sexual partner. Spores are also more likely to spread autonomously, such as via wind, than to rely on other organisms such as animal carriers to spread.
5. Fragmentation. In fragmentation, a “parent” organism is split into multiple parts, each of which grows to become a complete, independent “offspring” organism. This process resembles budding and vegetative propagation, but with some differences.
For one, fragmentation may not be voluntary on the part of the “parent” organism. Earthworms and many plants and sea creatures are capable of regenerating whole organisms from fragments following injuries that split them into multiple pieces.
When fragmentation does occur voluntarily, the same parent organism may split into many roughly equal parts in order to form many offspring. This is different from the processes of budding and vegetative propagation, where an organism grows new parts which are small compared to the parent and which are intended to become offspring organisms.
6. Agamenogenesis. Agamenogenesis is the reproduction of normally sexual organisms without the need for fertilization. There are several ways in which this can happen.
In parthenogenesis, an unfertilized egg begins to develop into a new organism, which by necessity possesses only genes from its mother.
This occurs in a few species of all-female animals, and in females of some animal species when there are no males present to fertilize eggs.
In apomoxis, a normally sexually reproducing plant reproduces asexually, producing offspring that are identical to the parent plant, due to lack of availability of a male plant to fertilize female gametes.
In nucellar embryony, an embryo is formed from a parents’ own tissue without meiosis or the use of reproductive cells. This is primarily known to occur in citrus fruit, which may produce seeds in this way in the absence of male fertilization.
Examples of Asexual Reproduction
All bacteria reproduce through asexual reproduction, by splitting into two “daughter” cells that are genetically identical to their parents.
Some bacteria can undergo horizontal gene transfer – in which genetic material is passed “horizontally” from one organism to another, instead of “vertically” from parent to child. Because they have only one cell, bacteria are able to change their genetic material as mature organisms.
The process of genetic exchange between bacterial cells is sometimes referred to as “sex,” although it is performed to change the genotype of a mature bacterium, not as a means of reproduction.
Bacteria can afford to use this survival strategy because their extremely rapid reproduction makes harmful genetic mutations – such as copying errors or horizontal gene transfer gone wrong – inconsequential to the whole population. As long as a few individuals survive mutation and calamity, those individuals will be able to rebuild the bacterial population quickly.
This strategy of “reproduce fast, mutate often” is a major reason why bacteria are so quick to develop antibiotic resistance. They have also been seen to “invent” whole new biochemistries in the lab, such as one species of bacteria that spontaneously acquired the ability to perform anaerobic respiration.
This strategy would not work well for an organism that invests highly in the survival of individuals, such as multicellular organisms.
Slime molds are a fascinating organism that sometimes behave like a multicellular organism, and sometimes behave like a colony of single-celled organisms.
Unlike animals, plants, and fungi, the cells in a slime mold are not bound together in a fixed shape and dependent on each other for survival. The cells that make up a slime mold are capable of living individually and may spread or separate when food is abundant, much like individuals in a colony of bacteria.
But slime mold cells are eukaryotic, and can display a high degree of cooperation to the point of creating a temporary extracellular matrix and a “body” which may become large and complex. Slime molds whose cells are working cooperatively can be mistaken for fungi, and can perform locomotion.
Slime molds can produce spores much like a fungus, and they can also reproduce through fragmentation. Environmental causes or injury may cause a slime mold to disperse into many parts, and units as small as a single cell may grow into a whole new slime mold colony/organism.
New Mexico Whiptail Lizards
This species of lizard was created by the hybridization of two neighboring species. Genetic incompatibility between the hybrid parents made it impossible for healthy males to be born: however, the female hybrids were capable of parthenogenesis, making them a reproductively independent population.
All New Mexico whiptail lizards are female. New members of the species can be created through hybridization of the parent species, or through parthenogenesis by female New Mexico whiptails.
Possibly as a remnant of their sexually reproducing past, New Mexico whiptail lizards do have a “mating” behavior which they must go through to reproduce. Members of this species are “mated with” by other members, and the lizard playing the female role will go onto lay eggs.
It is thought that the mating behavior stimulates ovulation, which can then result in a parthenogenic pregnancy. The lizard playing the “male” role in the courtship does not lay eggs.
Related Biology Terms
- Gamete – Sexual reproductive cells, which contain half of the parent organism’s genetic material.
- Reproductive strategy – A strategy that describes how a given population uses its resources to produce offspring.
- Sexual Reproduction – A means of reproduction in which the genetic material of two parents is combined to produce offspring with a unique genetic profile.
1. Which of the following is NOT an advantage of asexual reproduction?
A. Rapid reproduction.
B. High genetic diversity.
C. No need for a mate.
D. Low resource investment in offspring.
Answer to Question #1
B is correct. High genetic diversity is a characteristic of sexual reproduction, whereas low genetic diversity is a characteristic of asexual reproduction.
2. Which of the following events was NOT caused by low genetic diversity due to asexual reproduction?
A. The Irish Potato Famine
B. The disappearance of the Gros-Michel banana
C. The Black Death in England
D. A and B
Answer to Question #2
The Gros-Michel banana was not so lucky when it was hit by Panama Disease, and almost all specimens of the plant, which were genetically identical due to asexual reproduction, were killed. The same problem of asexual reproduction resulted in the deaths of most potato crops due to fungal infection, and subsequently in mass starvation, in the Irish Potato Famine.
3. Which of the following is NOT true of asexual reproduction?
A. Some organisms can only perform asexual reproduction because their genetics does not allow for the existence of healthy males.
B. Some organisms can perform both sexual and asexual reproduction.
C. It is used by a variety of organisms, including all bacteria and some plants, animals,and fungi.
D. It is used only by single-celled organisms.
Answer to Question #3
D is correct. Asexual reproduction is the only means of reproduction for prokaryotes, but some eukaryotes, including many plants, many sea creatures, and some land animals are also capable of reproducing asexually.