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Reproduction is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or 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.
Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders and other consequences that may arise from expression of deleterious or recessive traits resulting from incestuous sexual relationships and consanguinity. Animals avoid incest only rarely.
Self-pollination is a form of pollination in which pollen from the same plant arrives at the stigma of a flower or at the ovule. There are two types of self-pollination: in autogamy, pollen is transferred to the stigma of the same flower; in geitonogamy, pollen is transferred from the anther of one flower to the stigma of another flower on the same flowering plant, or from microsporangium to ovule within a single (monoecious) gymnosperm. Some plants have mechanisms that ensure autogamy, such as flowers that do not open (cleistogamy), or stamens that move to come into contact with the stigma. The term selfing that is often used as a synonym, is not limited to self-pollination, but also applies to other types of self-fertilization.
Plant reproductive morphology is the study of the physical form and structure of those parts of plants directly or indirectly concerned with sexual reproduction.
Self-incompatibility (SI) is a general name for several genetic mechanisms that prevent self-fertilization in sexually reproducing organisms, and thus encourage outcrossing and allogamy. It is contrasted with separation of sexes among individuals (dioecy), and their various modes of spatial (herkogamy) and temporally (dichogamy) separation.
Dioecy is a characteristic of a species, meaning that it has distinct individual organisms (unisexual) that produce male or female gametes, either directly or indirectly. Dioecious reproduction is biparental reproduction. Dioecy has costs, since only about half the population directly produces offspring. It is one method for excluding self-fertilization and promoting allogamy (outcrossing), and thus tends to reduce the expression of recessive deleterious mutations present in a population. Plants have several other methods of preventing self-fertilization including, for example, dichogamy, herkogamy, and self-incompatibility.
Sequential hermaphroditism is a type of hermaphroditism that occurs in many fish, gastropods, and plants. Sequential hermaphroditism occurs when the individual changes its sex at some point in its life. In particular, a sequential hermaphrodite produces eggs and sperm at different stages in life. Species that can undergo these changes from one sex to another do so as a normal event within their reproductive cycle that is usually cued by either social structure or the achievement of a certain age or size.
Genetic load is the difference between the fitness of an average genotype in a population and the fitness of some reference genotype, which may be either the best present in a population, or may be the theoretically optimal genotype. The average individual taken from a population with a low genetic load will generally, when grown in the same conditions, have more surviving offspring than the average individual from a population with a high genetic load. Genetic load can also be seen as reduced fitness at the population level compared to what the population would have if all individuals had the reference high-fitness genotype. High genetic load may put a population in danger of extinction.
Inbreeding depression is the reduced biological fitness which has the potential to result from inbreeding. Biological fitness refers to an organism's ability to survive and perpetuate its genetic material. Inbreeding depression is often the result of a population bottleneck. In general, the higher the genetic variation or gene pool within a breeding population, the less likely it is to suffer from inbreeding depression, though inbreeding and outbreeding depression can simultaneously occur.
Silene latifolia subsp. alba, the white campion is a dioecious flowering plant in the family Caryophyllaceae, native to most of Europe, Western Asia and Northern Africa. It is a herbaceous annual, occasionally biennial or a short-lived perennial plant, growing to between 40–80 centimetres tall. It is also known in the US as bladder campion but should not be confused with Silene vulgaris, which is more generally called bladder campion.
Ciona is a genus of sea squirts in the family Cionidae.
Out-crossing or out-breeding is the technique of crossing between different breeds. This is the practice of introducing distantly related genetic material into a breeding line, thereby increasing genetic diversity.
Environmental sex determination is the establishment of sex by a non-genetic cue, such as nutrient availability, experienced within a discrete period after fertilization. Environmental factors which often influence sex determination during development or sexual maturation include light intensity and photoperiod, temperature, nutrient availability, and pheromones emitted by surrounding plants or animals. This is in contrast to genotypic sex determination, which establishes sex at fertilization by genetic factors such as sex chromosomes. Under true environmental sex determination, once sex is determined, it is fixed and cannot be switched again. Environmental sex determination is different from some forms of sequential hermaphroditism in which the sex is determined flexibly after fertilization throughout the organism’s life.
Androdioecy is a reproductive system characterized by the coexistence of males and hermaphrodites. Androdioecy is rare in comparison with the other major reproductive systems: dioecy, gynodioecy and hermaphroditism. In animals, androdioecy has been considered a stepping stone in the transition from dioecy to hermaphroditism, and vice versa.
Inbreeding avoidance, or the inbreeding avoidance hypothesis, is a concept in evolutionary biology that refers to the prevention of the deleterious effects of inbreeding. Animals only rarely exhibit inbreeding avoidance. The inbreeding avoidance hypothesis posits that certain mechanisms develop within a species, or within a given population of a species, as a result of assortative mating, natural and sexual selection in order to prevent breeding among related individuals in that species or population. Although inbreeding may impose certain evolutionary costs, inbreeding avoidance, which limits the number of potential mates for a given individual, can inflict opportunity costs. Therefore, a balance exists between inbreeding and inbreeding avoidance. This balance determines whether inbreeding mechanisms develop and the specific nature of said mechanisms.
Exposure of zebrafish to a chemical environmental agent, analogous to that caused by anthropogenic pollution, amplified the effects of inbreeding on key reproductive traits. Embryo viability was significantly reduced in inbred exposed fish and there was a tendency for inbred males to sire fewer offspring.
Autogamy, or self-fertilization, refers to the fusion of two gametes that come from one individual. Autogamy is predominantly observed in the form of self-pollination, a reproductive mechanism employed by many flowering plants. However, species of protists have also been observed using autogamy as a means of reproduction. Flowering plants engage in autogamy regularly, while the protists that engage in autogamy only do so in stressful environments.
A mixed mating system, also known as “variable inbreeding” a characteristic of many hermaphroditic seed plants, where more than one means of mating is used. Mixed mating usually refers to the production of a mixture of self-fertilized (selfed) and outbred (outcrossed) seeds. Plant mating systems influence the distribution of genetic variation within and among populations, by affecting the propensity of individuals to self-fertilize or cross-fertilize . Mixed mating systems are generally characterized by the frequency of selfing vs. outcrossing, but may include the production of asexual seeds through agamospermy. The trade offs for each strategy depend on ecological conditions, pollinator abundance and herbivory and parasite load. Mating systems are not permanent within species; they can vary with environmental factors, and through domestication when plants are bred for commercial agriculture.
Reproductive assurance occurs as plants have mechanisms to assure full seed set through selfing when outcross pollen is limiting. It is assumed that self-pollination is beneficial, in spite of potential fitness costs, when there is insufficient pollinator services or outcross pollen from other individuals to accomplish full seed set.. This phenomenon has been observed since the 19th century, when Darwin observed that self-pollination was common in some plants. Constant pollen limitation may cause the evolution of automatic selfing, also known as autogamy. This occurs in plants such as weeds, and is a form of reproductive assurance. As plants pursue reproductive assurance through self-fertilization, there is an increase in homozygosity, and inbreeding depression, due to genetic load, which results in reduced fitness of selfed offspring. Solely outcrossing plants may not be successful colonizers of new regions due to lack of other plants to outcross with, so colonizing species are expected to have mechanisms of reproductive assurance - an idea first proposed by Herbert Baker and referred to as Baker's Law. Baker’s Law predicts that reproductive assurance should be common in weedy plants that persist by colonizing new sites. As plants evolve towards increase self-fertilization, energy is redirected to seed production rather than characteristics that increased outcrossing, such as floral attractants, which is a condition known as the selfing syndrome.
Cryptic self-incompatibility (CSI) is the botanical expression that's used to describe a weakened self-incompatibility (SI) system. CSI is one expression of a mixed mating system in flowering plants. Both SI and CSI are traits that increase the frequency of fertilization of ovules by outcross pollen, as opposed to self-pollen.
References
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- ↑ "cross-fertilization". www.britannica.com. Encyclopaedia Britannica. Retrieved 2022-03-16.
- ↑ Jarne, Philippe; Finot, Luc; Delay, Bernard; Thaler, Louis (1991). "Self-Fertilization Versus Cross-Fertilization in the Hermaphroditic Freshwater Snail Bulinus globosus". Evolution. 45 (5): 1136–1146. doi:10.2307/2409721. ISSN 0014-3820. JSTOR 2409721. PMID 28564176.
- 1 2 Lloyd, David G.; Schoen, Daniel J. (1992). "Self- and Cross-Fertilization in Plants. I. Functional Dimensions". International Journal of Plant Sciences. 153 (3): 358–369. doi:10.1086/297040. ISSN 1058-5893. JSTOR 2995676. S2CID 85344103.
- ↑ Mikami, Kazuyuki (2000), Tarín, Juan J.; Cano, Antonio (eds.), "Fertilization in Protozoa", Fertilization in Protozoa and Metazoan Animals: Cellular and Molecular Aspects, Berlin, Heidelberg: Springer, pp. 1–25, doi:10.1007/978-3-642-58301-8_1, ISBN 978-3-642-58301-8 , retrieved 2022-03-16
- ↑ Arriola, Paul E.; Ellstrand, Norman C. (1997). "Fitness of Interspecific Hybrids in the Genus Sorghum: Persistence of Crop Genes in Wild Populations". Ecological Applications. 7 (2): 512–518. doi:10.2307/2269516. ISSN 1051-0761. JSTOR 2269516.
- ↑ Baird, Wm. Vance; Riopel, James L. (1986). "Life History Studies of Conopholis americana (Orobanchaceae)". The American Midland Naturalist. 116 (1): 140–151. doi:10.2307/2425946. ISSN 0003-0031. JSTOR 2425946.
- ↑ Bernstein H, Hopf FA, Michod RE (1987). "The molecular basis of the evolution of sex". Adv. Genet. Advances in Genetics. 24: 323–70. doi:10.1016/S0065-2660(08)60012-7. ISBN 9780120176243.
- ↑ Michod, R.E. (1994). "Eros and Evolution: A Natural Philosophy of Sex" Addison-Wesley Publishing Company, Reading, Massachusetts. ISBN 978-0201442328
- ↑ Willis, John H. (1993). "Partial self-fertilization and inbreeding depression in two populations of Mimulus guttatus". Heredity. 71 (2): 145–154. doi:10.1038/hdy.1993.118. ISSN 1365-2540. S2CID 1461571.
- 1 2 Teixeira S, Foerster K, Bernasconi G (2009). "Evidence for inbreeding depression and post-pollination selection against inbreeding in the dioecious plant Silene latifolia". Heredity (Edinb). 102 (2): 101–12. doi: 10.1038/hdy.2008.86 . PMID 18698334.
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