Allogamy

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Allogamy or cross-fertilization is the fertilization of an ovum from one individual with the spermatozoa of another. [1] [2] By contrast, autogamy is the term used for self-fertilization. [1] In humans, the fertilization event is an instance of allogamy. Self-fertilization occurs in hermaphroditic organisms where the two gametes fused in fertilization come from the same individual. [3] This is common in plants (see Sexual reproduction in plants) and certain protozoans. [4] [5]

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In plants, allogamy is used specifically to mean the use of pollen from one plant to fertilize the flower of another plant and usually synonymous with the term "cross-fertilization" or "cross-pollination" (outcrossing). [4] The latter term can be used more specifically to mean pollen exchange between different plant strains or even different plant species (where the term cross-hybridization can be used) rather than simply between different individuals. [6]

Allogamy is achieved through the use of external pollinating factors. The process of allogamy involves two types of external pollinating agents, known as abiotic agents and biotic agents. The abiotic agents are water and wind. The biotic agents are insects and animals, which include bees, butterflies, snails, and birds. Wind pollination is referred to as anemophily, and water pollination is referred to as hydrophilly. Insect pollination is referred to as entomophily, bird pollination is referred to as omithophily, and snail pollination is referred to as malacophily. [7]

Allogamy can lead to homozygosity. After reaching homozygosity, the species develop homozygous balance and fail to exhibit inbreeding depression. Mechanisms that promote self-pollination include homogamy, bisexuality, cleistogamy, the position of anthers, and chasmogamy. [8]

Allogamy promotes genetic diversity and reduces the risk of inbreeding depression. The persistent prevalence of allogamy throughout different species implies that this strategy provides selective advantages concerning adaptation to changing environments and sustaining fitness. [9]

Parasites having complex life cycles can pass through alternate stages of allogamous and autogamous reproduction, and the description of a hitherto unknown allogamous stage can be a significant finding with implications for human disease. [10]

Avoidance of inbreeding depression

Allogamy ordinarily involves cross-fertilization between unrelated individuals leading to the masking of deleterious recessive alleles in progeny. [11] [12] By contrast, close inbreeding, including self-fertilization in plants and automictic parthenogenesis in hymenoptera, tends to lead to the harmful expression of deleterious recessive alleles (inbreeding depression). [13]

In dioecious plants, the stigma may receive pollen from several different potential donors. As multiple pollen tubes from the different donors grow through the stigma to reach the ovary, the receiving maternal plant may carry out pollen selection favoring pollen from less related donor plants. [14] Thus post-pollination selection may occur in order to promote allogamy and avoid inbreeding depression. Also, seeds may be aborted selectively depending on donor–recipient relatedness. [14]

See also

Related Research Articles

<span class="mw-page-title-main">Reproduction</span> Biological process by which new organisms are generated from one or more parent organisms

Reproduction is the biological process by which new individual organisms – "offspring" – are produced from their "parent" or parents. There are two forms of reproduction: asexual and sexual.

<span class="mw-page-title-main">Inbreeding</span> Reproduction by closely related organisms

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 recessive traits resulting from incestuous sexual relationships and consanguinity. Animals avoid inbreeding only rarely.

<span class="mw-page-title-main">Self-pollination</span> Form of

Self-pollination is a form of pollination in which pollen from one plant arrives at the stigma of a flower or at the ovule of the same plant. The term cross-pollination is used for the opposite case, where pollen from one plant moves to a different plant.

<span class="mw-page-title-main">Plant reproductive morphology</span> Parts of plant enabling sexual reproduction

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 temporal (dichogamy) separation.

Dioecy is a characteristic of certain species that have distinct unisexual individuals, each producing either male or female gametes, either directly or indirectly. Dioecious reproduction is biparental reproduction. Dioecy has costs, since only the female part of 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.

<span class="mw-page-title-main">Sequential hermaphroditism</span> Sex change as part of the normal life cycle of a species

Sequential hermaphroditism is one of the two types of hermaphroditism, the other type being simultaneous hermaphroditism. It occurs when the organism's sex changes at some point in its life. A sequential hermaphrodite produces eggs and sperm at different stages in life. Sequential hermaphroditism occurs in many fish, gastropods, and plants. Species that can undergo these changes do so as a normal event within their reproductive cycle, usually cued by either social structure or the achievement of a certain age or size. In some species of fish, sequential hermaphroditism is much more common than simultaneous hermaphroditism.

<span class="mw-page-title-main">Anemophily</span> Wind pollination

Anemophily or wind pollination is a form of pollination whereby pollen is distributed by wind. Almost all gymnosperms are anemophilous, as are many plants in the order Poales, including grasses, sedges, and rushes. Other common anemophilous plants are oaks, pecans, pistachios, sweet chestnuts, alders and members of the family Juglandaceae. Approximately 12% of plants across the globe are pollinated by anemophily, including cereal crops like rice and corn and other prominent crop plants like wheat, rye, barley, and oats. In addition, many pines, spruces, and firs are wind-pollinated.

Geitonogamy is a type of self-pollination. Geitonogamous pollination is sometimes distinguished from the fertilizations that can result from it, geitonogamy. If a plant is self-incompatible, geitonogamy can reduce seed production.

<i>Ciona</i> Genus of tunicate

Ciona is a genus of sea squirts in the family Cionidae.

<span class="mw-page-title-main">Flower</span> Reproductive structure in flowering plants

A flower, also known as a bloom or blossom, is the reproductive structure found in flowering plants. Flowers consist of a combination of vegetative organs – sepals that enclose and protect the developing flower, petals that attract pollinators, and reproductive organs that produce gametophytes, which in flowering plants produce gametes. The male gametophytes, which produce sperm, are enclosed within pollen grains produced in the anthers. The female gametophytes are contained within the ovules produced in the carpels.

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.

<span class="mw-page-title-main">Chasmogamy</span> Flowers with exposed reproductive parts

Chasmogamy is the type of plant reproduction in which the flowers open up, enabling cross-pollination. This is in contrast to cleistogamy, in which the flowers stay closed and self-pollinate.

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 and natural and sexual selection, in order to prevent breeding among related individuals. 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 such mechanisms.

Inbreeding in fish is the mating of closely related individuals, leading to an increase in homozygosity. Repeated inbreeding generally leads to morphological abnormalities and a reduction in fitness in the offspring. In the wild, fish have a number of ways to avoid inbreeding, both before and after copulation.

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.

<span class="mw-page-title-main">Mixed mating systems</span> Plants which reproduce in multiple ways

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 G. Baker and referred to as Baker's "law" or "rule". Baker's law predicts that reproductive assurance affects establishment of plants in many contexts, including spread by weedy plants and following long-distance dispersal, such as occurs during island colonization. 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.

Gametophytic selection is the selection of one haploid pollen grain over another through the means of pollen competition, and that resulting sporophytic generations are positively affected by this competition. Evidence for the positive effects of gametophytic selection on the sporophyte generation has been observed in several flowering plant species, but there are is still some debate as to the biological significance of gametophytic selection.

References

  1. 1 2 Martin, Elizabeth; Hine, Robert (2015-09-17), Martin, Elizabeth; Hine, Robert (eds.), "fertilization", A Dictionary of Biology, Oxford University Press, doi:10.1093/acref/9780198714378.001.0001, ISBN   978-0-19-871437-8 , retrieved 2022-03-16
  2. ↑ "cross-fertilization". www.britannica.com. Encyclopaedia Britannica. Retrieved 2022-03-16.
  3. ↑ 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.
  4. 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.
  5. ↑ 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
  6. ↑ 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.
  7. ↑ Panawala, Lakna (2017). "Difference Between Allogamy and Xenogamy".
  8. ↑ "Crop Improvement: Mode of Pollination".
  9. ↑ Ariane, Mendes (2024). "Mating System Analysis and Genetic Diversity of Parkia Multijuga Benth. One Native Tree Species of the Amazon". Forests. 15 (1): 172. doi: 10.3390/f15010172 . ProQuest   2918759358.
  10. ↑ 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.
  11. ↑ Bernstein H, Hopf FA, Michod RE (1987). "The Molecular Basis of the Evolution of Sex". Molecular Genetics of Development. Advances in Genetics. Vol. 24. pp. 323–70. doi:10.1016/S0065-2660(08)60012-7. ISBN   9780120176243. PMID   3324702.
  12. ↑ Michod, R.E. (1994). "Eros and Evolution: A Natural Philosophy of Sex" Addison-Wesley Publishing Company, Reading, Massachusetts. ISBN   978-0201442328
  13. ↑ 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.
  14. 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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