4 April,2014
Pollination can simply be described as a mechanism that involves the transfer of pollen contribute to the process of reproduction of plants. this process in plants reproduction entails ferterlization and reproduction (Barret). In scientific terms or biological terms, pollination can be described as the movement or transfer of pollen from one flower's anther to the stigma of same or other flower. This process or step is a pre-requisite for the ferterlization because it allows the fusion of the nuclei from one pollen grain with the nuclei of the ovule of the flower of other plant. The whole essence of the pollination is that it allows ferterlization to occur with subsequent development of seeds. In this process of pollination, some flowers tend to develop seeds based on the strategies involve in their pollination which is a type of self pollination when both the pollen and pistil are from the same plant (Carter). In the second type or strategies of pollination, pollens need to move from one plant to pistil in another plants via several forms of mechanisms. Those mechanisms involve in the movement of pollens also contribute to the evolution of different forms of generation (Randall et al.).
The increasing level of complexity that exist within the plant generation or organization can be attributed to the action of earliest pollinators which are plants that helps to transfer pollens. This evolution allows the changes we see in plants today to evolve simply because it wasn’t there before considering what is found in plants such as algal mats, bryophytes and ferns. There are several others that have now evolved into the gymnosperms and angiosperms we now see in the plant kingdom in recent times (Carter).
Types
Abiotic
There are different types of pollination. We have abiotic and biotic. Abiotic pollination is the type of pollinations that simply refers to type whereby pollination occurs without the involvement of organisms. This type of pollination only occurs in few flowering plants. Anemophily denotes the winds pollinations and this is the most common form of abiotic pollination. It is what is seen in grasses, most conifers, and most deciduous trees. Another form of abiotic pollination involving non-organism mode is the hydrophily pollination, which is the pollination by water (Friedman & Barrett). This pollination by water is that which occurs in aquatic plants. It happens by making aquatic plants to release their pollen into the surrounding water directly.
Biotic
The majority of the plant gets pollinated via biotic form of pollination. The type of biotic pollination, which tend to occur in gymnosperm are a form of incidental biotic pollination. In this scenario, the pollination just occur incidentally. However, there are several gymnosperm that gets their pollinators adapted mutually. The best of the order in this category is the order Cycadales which tend to be linked to the species of bee
tles. The coniferas are anemophilous in their forms of pollinations.
The common type is the biotic type which allows pollinations to be made by a living organism which help by carrying or moving the pollen grain from one part to another on a single plant or one plant to another. There are specific traits of plants that usually attract one type of pollinator or another and this is usually tagged the pollination syndrome. Globally, there are thousands of pollinators with specific plants they are used to or normally pollinate.
Another form of pollination is the Entomophily which simply described the form of pollination done by insects such as the bees,wasps and occasionally by ants, beetles, moth, butterflies, and flies (Thompson & Wilson). Insect pollinations as always, been one major form of pollination since ancient times. This group of biotic pollination has a major role to play in the evolution of the plants.
While in zoophily form of pollination, animals play a major role, hence this is usually tagged as being performed by vertebrates such as birds and bats, particularly, hummingbirds, Sunbirds, Spiderhunters, Honeyeaters, and fruit bats (Fleming & Kress). Those types of plants adapted to using bats or moths as pollinators typically have white petals and a strong scent, whereas plants that use birds as pollinators tend to develop red petals and rarely develop a scent (few birds rely on a sense of smell to find plant-based food). The human types of pollination is the anthropophily (Pollination by humans), and this type of pollination has been often artificial pollination used in hybridization techniques.
Flower constancy which is used to describe a situation where pollinators transfer pollen to specific plants are noted to be achieved by pollinators such as honeybees, bumblebees and butterflies. This is found to be beneficial to the specific pollinators because of the prevention of loss of pollen especially from interspecific flights.
The Evolution linked to pollination
Several changes had occurred relating to the fossil record. In terms of abiotic pollination and the existence of such type of pollination. Fern-like plants are those first linked to such fossil record and linked to the abiotic pollination, especially in the period of late Carboniferous period. During the Triassic period is when the gymnosperms actually showed evidence of relating to biotic forms of pollination. It is also important to note that most of the fossilized pollen grains tend to show features that is similar to the biotically dispersed pollen. There are some features located on the organism that acknowledge that they are once early pollinators. Such body parts are the gut content,wing structures and mouthpart. Another indicator that shows the relationship between the beetles and angiosperms in the earlier period (Cretaceous period) is the parallel radiations of angiosperms and insects into the late Cretaceous period. The nectaries evolution late into this period indicated the start of mutualism relationship between the hymenopterans and angiosperms.
The process of plant pollination
This process usually occurs in several ways. Humans have the potential of transferring plant pollen from a plant flower to another, but most of the pollination process that occur in plants usually occur without the contribution of human beings.This simply take up the other processes where such plants rely on non human methods which is either biotic or abiotic methods. This is especially via the wind and animal methods.
The process of pollination involving the animals such as bees, butterflies,moths, flies and hummingbirds is a form of accidental pollination simply because their aim or target for moving onto the plant is solely for the nectar, to get food or the sticky pollen. It is the process of getting those that led to the eventual movement of the pollen to other receptive site. The process occurs simply because while the animals are feeding on the nectar, the body accidentally rub against the stamens which contain the pollens, this then result in a situation where the body rub on the pollen. When they move to another site to another food or nectar, pollen on the skin then can rub off onto the new stigma with ease. It is important to note that plant’s pollinated by animals are usually brightly colored with the very strong attractive smell. While it is noted that plant that are pollinated by the wind are usually of long stamens and pistils and are easily dispersed from one plant to another. They are usually of dull color with unscented flowers and small petals that has no room for any insect to land.
Evolution of plant
Pollination and evolution as always, being related considering the effect of pollination on evolution and how various plants had evolved to adapt with the needs of the available pollinators. It is important for us to understand that the first fossil record for abiotic pollination is from fern-like plants in the late Carboniferous period. This simply described how long abiotic pollination has been in existence and the changes that later ensue to give room for the biotic pollinators.
Gymnosperms also show some level of evidence for the occurrence of biotic pollination as early as the Triassic period although no specific plant was indicated to be pollinated directly by by such pollinators. However, many fossilized pollen grains from different plants show characteristic level that are similar to the biotically dispersed pollens we see today.
Pollination strategies
The two major types of pollination strategies are the cross pollination and self-pollination. There are positive cross pollinations where their resultant combination of genes which occur during pollination and then produces offspring. The major effect of that genetic combination is that the newly formed offspring are better adapted to their environment than the parents.
In case of the negative cross pollination, there is the resultant formation of an offspring which is formed by a combination of genes that are less adapted to their environment when compared with their parent’s environmental adaptation.
The aspect of the self pollination is that which is characterized by the presence of the matured stamen and style of flowers that are usually synchronized. The proteins on the stigma and styles are types that also must be compatible. The proteins in the pollen also need to be compatible for effective pollination.
Flowering time
There are several other factors that influence the flowering times. This is usually based on the natural selection process, but respond to some external factors such as temperature, light intensity, presence of pollinators and environmental signal. The implication of this response is that when there are no pollinators, there is no need for flowering.
Theories of flower evolution
Several flower evolution theories have been proposed. Two of those theories are listed below. The anthophye theory, and mostly male theory. The Anthophyte theory is a flowering theory that is based on the observation of the Gnetales (a group of gymnosperms with flower like ovule). This group of flowers has partially developed a structure like a vessel which resembles that found in the angiosperms and megasporangium being covered the 3 envelopes that also resembles the ovary structure of the angiosperm flowers. Many studies conducted, however, have not shown any definite similarities or evidence showing Gnetales relates to the angiosperms but there are several showing they are not related.
Regarding the Mostly Male Theory, there is more of a genetic basis for the theory. The proponents of the theory simply described it that gymnospersm are with two similar copies of gene LFY while the angiosperms are made with only one. The theory descriptions show that the implication for the presence of single copy of gene is simply a loss of one copy which is described by the molecular clock analysis. The loss occurs during the same time the flower fossils became abundant suggesting a form of evolutionary process during that period. From the deductions of the theory, loss which led to one gene copy is what led to flower that were more male with its ovules being expressed ectopically. This ovules also inherited the character of attracting pollinators and somewhat later period in the evolutionary process, there is the integration of some of the ovules into the core part of the flower.
Shape considerations
The pollination strategies influence how the flower has to be designed. This goes away like a form of adaptation or evolution to accommodate the vector. This change in the flower, then result in prevention of pollen and nectar robbers from stealing the rewards. The shape that is being formed by the flowers can also make it more attractive. Flowers that are being pollinated by hovering pollinators tend to hang down and have long styles and filaments while those that are pollinated by hungry beetles are the type of flowers that need to provide lots of structural food that will attract and feed (and yet protect the ovules!). A beetle-pollinated flower is also the type that needs to create an easy entrance for the beetles which have more of clumsy flight.
In case of non-hovering insects and birds, there is a need for perches or landing platforms on any plants they want to pollinate. Those parts of the flower must posses the sizes and shapes of the flower parts that are good for their landing and their alignments are critical to assure pollination when the vector does visit. It is also found out that flowers with long nectar spur help protects the reward from robbers while giving the opportunities to those that actually needs it i.e. yet allows reward for the actual vector.
Adaptations of Flowers for Given Pollinators
It is also very important to understand that the type of flower structural adaptation usually depends more on the type of pollinator and what is needed to attract such pollinators. Different pollinators have their adaptations too in relations to the flower they usually pollinate or the form of nectar they are after. For instance, if we consider the Bees, it can be seen that Bees usually don't see red, but do see blue, yellow and ultraviolet colors (Michigan State University). The implication of this is that the flowers they are after will be of such colors. The scent coming from the flowers is also a form of delicate sweet scent that can be perceived by the Bees. The nectar is usually at the end point of the floral tube and it possesses a structural make up which allows the pollinators tongue to fit easily.
In cases of butterflies that are diurnal, there is a good vision, but weaker sense of smell. These flowers that are being pollinated by butterflies are usually of brightly red colored, but odorless hence structured in a cluster form and a suitable landing pattern or form. Those flowers have evolved to allow the pollinators to move around on the flower. Compositae family are some of the members of the family that are being pollinated by butterflies. The evolutionary facts about group of flowers is that which relates to the formation of small flowers that are arranged in a flat top head pattern and clusters for better adaptation and pollination.
In terms of the Moth which are nocturnal pollinators, are linked with the evolutionary changes of those plants is that which relates to the fact that it does not make any sense to waste energy in the production of nectars or attractant during the day period without having nothing to use such attractants for.
There is a great interaction between plant pollinator interactions and the floral diversity. This underlies the major diversity in the angiosperm. The key floral trait play a major role in pollinator attraction. The pollinators mediate selection of floral traits that allows effective selection and adaptions. The selection imposed by different pollinators create a major influence on the response of the plants.
Work Cited
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Carter, Stein. J. Pollination and plant families. http://biology.clc.uc.edu/courses/bio106/pollinat.htm.
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Friedman,Janice & Barrett, Spencer. Wind of change: new insights on the ecology and evolution of pollination and mating in wind-pollinated plants. Annals of Botany. Oxford University Press. June 2009. Web. 6 April, 2014. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2701749/
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