Come, today we will read about Sexual Reproduction in Flowering Plants. Sexual selection is described as natural selection arising through a preference by one sex for certain characteristics in individuals of the other sex . Sexual selection is a common concept in animal evolution , but as with plants , it is often overlooked because many plants are bisexual . Flowering plants show many characteristics that are often selected for sexually. For example, flower symmetry, nectar production, floral structure, and inflorescence are just a few of the many secondary sexual characteristics carried out by sexual selection. Sexual dimorphism and reproductive organs can also be affected by sexual selection in flowering plants. [1]Therefore, sexual selection is a major driving feature of flower development. Let’s begin our topic of sexual reproduction in flowering plants
Mechanisms of sexual selection
There are two main mechanisms of sexual selection in flowering plants, one is inter-sexual competition and the other is the choice of female mates. Inter-sexual selection is responsible for floral development and diversification. Interracial selection with the help of pollinators has also produced some of the most notable examples of exaggerated traits among bisexual plants. Similarly, sexual dimorphism has probably been involved in the evolution of sexual dimorphism in the floral traits of dimorphic plants , and possibly also in the development of secondary sexual dimorphism through genetic correlations with floral traits. Sexual selection through female preference is probably a more difficult concept to apply to plants. There is evidence that the female (or the female function of the hermaphrodite) is particularly likable during fertilization. [2]These two mechanisms are the main driving forces of sexual selection in flowering plants.
Symmetry and Structure
Flower symmetry often acts by sexual selection. Flower characters are often subject to strong directional selection from pollinators, and this can disrupt developmental homeostasis in flowers that can develop into a large fraction of fluctuating heterozygosity. Fluctuational heterogeneity in floral traits can lead to sexual selection in plants if pollinators view symmetric flowers in a mixed manner. Several studies have shown that pollinators preferentially visit flowers in a more symmetrical floral pattern, and many are believed to explain why this pollination preference exists. First, the preference may exist because of positive reinforcement. From experience, pollinators can learn that asymmetrical flowers offer fewer rewards than symmetrical flowers. Second, sensitive sensory biases towards pollinators may cause them to select symmetrical flowers. This pollinator preference can lead to symmetrical flowers that are fertilized more often. This increase in fertilization frequency increases the amount of seeds produced, and consequently symmetrical,
Sexual dimorphism
There are many examples of sexual dimorphism in flowering plants . Sexual dimorphic differences include bud abortion, flower size, number of flowers per plant, floral longevity, nutrient content of flowers, nectar production, phenology and periodicity of flowers, floral aroma, floral defense against herbivores, and total flower count. , Contains various inflorescence features including daily display. shape, and inflorescence architecture. In animal-pollinated species, these differences affect the meeting of pollinators, competition for mates, and the development of sexual dimorphism. [4]However, there are restrictions on animal-pollinated species, as too much divergence can interfere with mating success if pollinators are more attracted to one sex than the other, or if sexes attract different pollinators. Such constraints are absent from wind-pollinated plants, and the contrasting biophysical requirements for pollen dispersal and pollen capture have led to striking cases of sexual dimorphism in plant architecture and flower production in some species. [4] Some typical examples of sexual dimorphism in flowering plants are given below.
Inflorescence
Inflorescences can be acted upon in a number of ways by sexual selection , and this usually involves arrangement, number, and size. [5] For example, in plants male inflorescences often produce more flowers than females. Furthermore, pollen export, and eventual paternity, often increases with the number of flowers, even for plants with bisexual flowers. Maintaining older flowers without pollinator rewards can increase pollinator visitation rates and increase pollen removal. Studies suggest that selection has been made for increased pollen distribution, achieved through greater inflorescence size, and it seems that male–male competition is usually part of that selection pressure.
Corolla
The corolla are the petals of the flower, and also undergo sexual selection. Traits such as color, size, shape and symmetry often counteract sexually selected pressure. An example is that male flowers are often larger than female flowers, at least in some species. Although this is probably achieved through resource allocation mechanisms, it is unlikely that resource allocation, from a lower cost of Androecium compared to gynoecium in males, to a greater expenditure on the corolla, is a general and complete explanation of the size difference. Some corolla enlargement may occur through selection on correlated traits such as pollen production. However, it is likely that male competition often contributes directly to the development of larger male corollas, especially where pollen availability is not limited.
Nectar production
Nectar production is different for each flowering plant, and there are many different selective forces acting on it. There is no specific evolutionary force that drives nectar production, but it is believed that sexual selection plays a major role. Studies have supported the idea that sexual selection is a possible explanation for at least some species with sex-biased nectar production. For example, gender-biased expression of nectar is often accompanied by similarly biased expression of other floral characteristics. A typical example comes from the flowers of Impatiens capensis ,And how they show longevity of the more beneficial male phase. In other species, petals may notably be observed to wilt during the less beneficial female phase or change color as they move to the less beneficial female phase. Much of the evidence for sexually selected nectar production depends on the specific behaviors of pollinators. If sexual selection currently maintains sex-biased nectar production, then pollinators should be able to differentiate between male and female stage flowers. They should also visit flowers preferably of more beneficial stage. For species that discriminate among pollinators, increased rewards may result in increased mating success, which would allow nectar to be a sexually selected trait.
Reproductive organs
Androecium often faces pressure from sexual selection. This is especially evident when pollen is produced; There can be multiple sources of sexual selection depending on the way pollen is presented to the pollen carriers. Since pollen is packaged in units that ensure that many pollen grains travel together in pollen grains , polyids, viscine threads, etc., the pollen donor blocks access by other males to the stigma and associated ovules.may be able to monopolize, unless selection is also made. The stigma is in favor of compensating for the increase. Furthermore, when pollen germination depends on some minimum number of pollen grains to overcome the stigma barrier, which is a mechanism that enhances male competition, there is a need for larger pollen dispersal units or some other pollen-delivery mechanism. may be selected for. If visits to pollen grains are few, selection is made to pack the pollen in such a way that all can be removed at once. When repeated pollinator visits are typical, there may be selection for different temporal patterns of pollen presentation and different modes of pollen delivery. Variation in stamen length affects pollen dispersal and potential male reproductive success both within and between flowers. Increasing the chance of parenthood by distributing pollen between pollinators can take different routes in different systems,[5] Jiangalso affected by sexual selection. Each part, from the ovary, sty, stigma and carpel, may face pressure from sexual selection. In ovule packaging, the intensity of pollen competition depends on the number of pollen grains relative to the number of ovules. Although many factors may contribute to determining ovule number, one way to increase the level of pollen competition for females is to reduce ovule number while maintaining stigma size. The development of functional syncope (assuming no other attendant changes) is probably a simultaneous increase in the number of oocytes accessible from a stigma, to reduce the intensity of pollen competition, and the concentration of pollen deposition on the same stigma. which is to increase pollen competition. Further increase in pollen competition Increased pollen distribution (through changes in pollination, increased attractiveness of flower display, or through rewards), a decrease in ovule number or stigma size, a change in the temporal pattern of stigma receptivity, or a change in stigma. In the competitive environment of Karpel.
