What is Self Fertilisation?
The uniting of male and female gametes and/or nuclei from the same haploid, diploid, or polyploid organism is known as selfing or self-fertilisation. It's a case of excessive inbreeding. From unicellular creatures to the most complex hermaphroditic plants and animals, selfing is common (especially invertebrates). Selfing can happen in unicellular organisms like Protozoa when two individuals (or their cell nuclei) that were formed from a previous mitotic division of the same individual interbreed.
Selfing plants account for about 10-15% of all blooming plants. Some hermaphrodite animals reproduce by self-fertilization on a regular basis. Selfing is more prevalent in adverse environmental conditions or the absence of a partner in other species; in such species, selfing is more common in bad environmental conditions or the absence of a mate.
Self-Fertilization in Plants
Selfing is a term that is frequently used as a synonym for self-pollination, although it also refers to various types of self-fertilization in plants and animals.
Self-pollination occurs when pollen from the same plant lands on the stigma of a flower (in blooming plants) or the ovule (in non-flowering plants) (in gymnosperms). 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 in autogamy; 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 Flowers that do not open (cleistogamy) or stamens that move to come into touch with the stigma are examples of autogamy processes in plants.
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Occurrence: Few plants pollinate themselves without the help of pollen carriers (such as wind or insects). The mechanism is most commonly seen in legumes like peanuts. The blooms of another legume, soybeans, bloom during the day and stay open to insect cross-pollination. If this isn't done, the flowers will self-pollinate as they close. Orchids, peas, sunflowers, and tridax are just a few of the plants that may self-pollinate. The majority of self-pollinating plants have small, inconspicuous blooms that release pollen straight onto the stigma before the bud opens. Self-pollinated plants use less energy to produce pollinator attractants and can thrive in environments where the insects and other animals that would visit them are sparse or non-existent, such as the Arctic or at high altitudes.
Self-pollination reduces the number of offspring available and may reduce plant vigour. Self-pollination, on the other hand, has the potential to benefit plants by allowing them to extend beyond the range of acceptable pollinators or generate offspring in locations where pollinator populations have been substantially reduced or are naturally changeable.
Types of Self-Pollinating Plants
Unless there is a mechanism to prevent it, both hermaphrodite and monoecious species have the potential for self-pollination and self-fertilization. Eighty percent of flowering plants are hermaphroditic, which means they have both sexes in the same flower, whereas only 5% are monoecious. As a result, the remaining 15% would be dioecious (each plant unisexual). Orchids and sunflowers are two examples of self-pollinating plants. Self-pollination and cross-pollination are both possible for dandelions.
Advantages: Self-pollinating flowers provide a number of advantages. For starters, if a genotype is well-suited to a certain habitat, self-pollination aids in the maintenance of this characteristic in the species. Because it is not reliant on pollinating agents, self-pollination can occur when bees and wind are unavailable. When the number of flowers is limited or they are spaced widely, self-pollination or cross-pollination can be beneficial. Pollen grains are not transported from one flower to another during self-pollination. As a result, there is less pollen waste. Self-pollinating plants also do not require external pollinators.
Disadvantages: Self-pollination has a number of drawbacks, including a lack of variation that prevents adaptability to changing environmental conditions or disease attack. Self-pollination can promote inbreeding depression because of the expression of detrimental recessive mutations, or diminished species health due to the breeding of closely related specimens. This is why many flowers with the capacity to self-pollinate have a built-in mechanism to prevent it, or at the very least make it a second choice. Genetic recombination cannot erase genetic abnormalities in self-pollinating plants, and children can only avoid acquiring the harmful traits through a fortuitous mutation in a gamete.
Self-Fertilization in Animals
Hermaphroditism is a condition in which a single animal possesses both male and female reproductive systems. Hermaphroditic invertebrates include earthworms, slugs, tapeworms, and snails. Hermaphrodites can self-fertilize, but they usually mate with another member of their species, fertilising and creating offspring together. Barnacles and clams, for example, are more likely to self-fertilize because they have limited movement or are not motile. Because self-fertilization is an extreme form of inbreeding that usually results in less fit offspring, many species have measures in place to avoid it.
FAQs on Self Fertilization
1. What is self-fertilization and how does it occur?
Self-fertilization, also known as selfing, is a mode of reproduction where the male and female gametes from the same individual fuse to form a zygote. It is an extreme form of inbreeding. This process is common in many organisms, including unicellular life forms, hermaphroditic animals (especially invertebrates), and a significant portion of flowering plants.
2. What are some common examples of self-fertilization in the plant kingdom?
Many plants have developed mechanisms to facilitate self-fertilization. Common examples include:
- Peas and Peanuts: These legumes often self-pollinate before their flowers even open, ensuring fertilization without external pollinators.
- Soybeans: While their flowers open to allow for cross-pollination by insects, they will self-pollinate as they close if cross-pollination has not occurred.
- Orchids and Sunflowers: Many species within these families are capable of self-pollination.
Some plants ensure self-fertilization through cleistogamy, where flowers do not open at all.
3. What is the main difference between self-fertilization and cross-fertilization?
The primary difference lies in the source of the gametes involved:
- Self-Fertilization: Involves the fusion of male and female gametes that originate from the same parent organism.
- Cross-Fertilization: Involves the fusion of gametes from two different parent organisms.
This fundamental difference means that cross-fertilization introduces new genetic combinations, increasing genetic diversity, while self-fertilization preserves the genetic makeup of a single parent.
4. Why does self-fertilization typically lead to a decrease in genetic diversity?
Self-fertilization reduces genetic diversity because the offspring inherit all their genetic material from a single parent. There is no introduction of new alleles or genetic combinations from another individual. Over successive generations, this process increases homozygosity (having two identical alleles for a particular gene), which can expose and fix deleterious recessive traits, a phenomenon known as inbreeding depression. The lack of variation makes the population more vulnerable to environmental changes and diseases.
5. What are the key advantages and disadvantages of self-fertilization for a species?
Self-fertilization offers a mix of benefits and drawbacks:
- Advantages: It is highly efficient as it does not depend on external pollinators (like wind or insects). It helps preserve well-adapted genotypes in a stable environment and allows isolated individuals to reproduce.
- Disadvantages: The main drawback is the lack of genetic variation, which limits a species' ability to adapt to changing conditions. It can also lead to inbreeding depression, reducing the overall health and vigour of the species over time.
6. How do some organisms prevent self-fertilization even if they are hermaphrodites?
Many hermaphroditic organisms have evolved mechanisms to avoid self-fertilization and promote genetic exchange. For example:
- Earthworms: They practice dichogamy, where the male and female reproductive organs mature at different times, making self-fertilization impossible.
- Snails: Land snails engage in reciprocal copulation, where they exchange bundles of sperm (spermatophores) with a partner.
- Plants: Many flowering plants use a genetic mechanism called self-incompatibility, where the pistil can recognize and reject pollen from the same plant.
7. Is self-fertilization possible in humans or other complex vertebrates?
No, self-fertilization is biologically impossible in humans and other complex vertebrates. These species are typically dioecious, meaning each individual has either male or female reproductive organs, but not both. Reproduction requires two separate individuals to contribute gametes (sperm and egg), a process known as cross-fertilization.
8. What is the difference between autogamy and geitonogamy in plants?
Both are types of self-pollination, but they differ in the specific process:
- Autogamy: This is when pollen from the anther of a flower is transferred to the stigma of the very same flower. It is functionally and genetically true self-pollination.
- Geitonogamy: This is when pollen from the anther of one flower is transferred to the stigma of another flower on the same plant. While it is ecologically a form of cross-pollination (as it may involve a pollinator), it is genetically identical to autogamy because the gametes come from the same parent plant.
9. Under what environmental conditions might self-fertilization be more advantageous than cross-fertilization?
Self-fertilization becomes a superior strategy under specific conditions. It is highly advantageous in stable environments where the parent's genetic makeup is already well-suited for survival. It also serves as a crucial survival mechanism in areas where pollinators are scarce or unreliable, such as in arctic regions, at high altitudes, or on isolated islands. By ensuring reproduction without a partner, it guarantees the continuation of the species when opportunities for cross-fertilization are limited.
