Pollen theft

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Trigona bees chew through unopened flowers to access pollen Arapuas nas flores de babosa.jpg
Trigona bees chew through unopened flowers to access pollen
Trigona bees chew through unopened flowers to access pollen Trigona Bee Visiting Justicia - Flickr - treegrow (3).jpg
Trigona bees chew through unopened flowers to access pollen

Pollen theft, also known as pollen robbery or floral larceny, occurs when an animal actively eats or collects pollen from a plant species but provides little or no pollination in return. Pollen theft was named as a concept at least as early as the 1980, [1] and examples have been documented well before that. For example, native honey bees were documented 'stealing' large amounts of pollen from the large, bat-pollinated flowers of Parkia clappertoniana in Ghana in the 1950s. [2] Nevertheless, pollen theft has typically received far less research attention than nectar robbing, despite the more direct consequences on plant reproduction.

Contents

Pollen thieves

Few pollen-collecting animals are obligate pollen thieves. Rather pollen theft generally arises from a mismatch between the morphology or behaviour of a pollen collecting animal and the morphology or phenology of a flowering plant species. [3] The clearest examples of pollen theft are when pollen-collecting insects visit only the male (pollen-bearing) plants of dioecious species, and so never come into contact with female flowers. [4] However pollen theft can also arise if pollen-collectors visit only male-phase (pollen-bearing) flowers of dichogamous species, or are too small to contact stigmas while collecting pollen from species with large or highly herkogamous flowers. [5] Pollen thieves include beetles, [6] flies, [7] thrips, [8] and even a parakeet, [9] but the vast majority documented so far have been bees. [10] These include Trigona species, which often bite through anthers to access pollen, [11] Halictids, [12] bumble bees, [13] and, most commonly of all, honey bees. [10] Honey bees are thought to be particularly common pollen thieves as they are behaviourally flexible, often visiting flowers in 'unexpected' ways that avoid floral mechanisms for ensuring pollen deposition, [14] or because they have been introduced by humans for agriculture and so more frequently encounter plants that have not evolved in their presence. [15] [4]

Impact on plant ecology and evolution

Because pollen serves as both an attractant to pollinators and as the carrier of male gametes (i.e. is directly evolved in plant sexual reproduction), loss of pollen to pollen theft can reduce the reproductive success of both individual plants and entire plant populations. An experiment in South Africa found that native pollen thieves (bees) significantly increased pollen removal but decreased pollen receipt and seed set in populations of bird-pollinated Aloe maculata. [16] In Brazil, exotic honey bees reduced pollen in anthers by 99% and were negatively correlated with seed set in the dioecious species Clusia arrudae. [4] In Australia, exotic honey bees were unable to collect pollen from buzz-pollinated anthers of Melasotma affine , so instead stole pollen that had already been deposited on stigmas, halving seed set when they were they last visitor. [15] In another Australian example, honey bees had no effect on reproduction in Grevillea barklyana when bird pollinators were common, but reduced seed set by 50% when bird pollinators were rare by preventing delayed autonomous self-pollination (ie disrupting reproductive assurance).

Honey bee collects pollen from male-phase flowers of Aloe. Honey bees often act as pollen thieves on bird-pollinated aloes in South Africa. Bee with pollen on aloe (5860287315).jpg
Honey bee collects pollen from male-phase flowers of Aloe. Honey bees often act as pollen thieves on bird-pollinated aloes in South Africa.

Pollen theft may strongly affect floral evolution whenever some plant individuals are more vulnerable than others. Whlle it is hard to hindcast why any modern traits evolved, several could have been selected on by pollen theft. [16] These include mechanisms to hide pollen, such as buzz-pollination [17] or pollen release that requires a forceful trigger, [6] or chemical deterrents in pollen. [18] [19]

Related Research Articles

<span class="mw-page-title-main">Honey bee</span> Colonial flying insect of genus Apis

A honey bee is a eusocial flying insect within the genus Apis of the bee clade, all native to mainland Afro-Eurasia. After bees spread naturally throughout Africa and Eurasia, humans became responsible for the current cosmopolitan distribution of honey bees, introducing multiple subspecies into South America, North America, and Australia.

<span class="mw-page-title-main">Pollinator</span> Animal that moves pollen from the male anther of a flower to the female stigma

A pollinator is an animal that moves pollen from the male anther of a flower to the female stigma of a flower. This helps to bring about fertilization of the ovules in the flower by the male gametes from the pollen grains.

<span class="mw-page-title-main">Petal</span> Part of most types of flower

Petals are modified leaves that surround the reproductive parts of flowers. They are often brightly colored or unusually shaped to attract pollinators. All of the petals of a flower are collectively known as the corolla. Petals are usually accompanied by another set of modified leaves called sepals, that collectively form the calyx and lie just beneath the corolla. The calyx and the corolla together make up the perianth, the non-reproductive portion of a flower. When the petals and sepals of a flower are difficult to distinguish, they are collectively called tepals. Examples of plants in which the term tepal is appropriate include genera such as Aloe and Tulipa. Conversely, genera such as Rosa and Phaseolus have well-distinguished sepals and petals. When the undifferentiated tepals resemble petals, they are referred to as "petaloid", as in petaloid monocots, orders of monocots with brightly colored tepals. Since they include Liliales, an alternative name is lilioid monocots.

<span class="mw-page-title-main">Pollination</span> Biological process occurring in plants

Pollination is the transfer of pollen from an anther of a plant to the stigma of a plant, later enabling fertilisation and the production of seeds, most often by an animal or by wind. Pollinating agents can be animals such as insects, for example beetles; birds, butterflies, and bats; water; wind; and even plants themselves. Pollinating animals travel from plant to plant carrying pollen on their bodies in a vital interaction that allows the transfer of genetic material critical to the reproductive system of most flowering plants. When self-pollination occurs within a closed flower. Pollination often occurs within a species. When pollination occurs between species, it can produce hybrid offspring in nature and in plant breeding work.

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

Buzz pollination or sonication is a technique used by some bees, such as solitary bees, to release pollen which is more or less firmly held by the anthers. The anthers of buzz-pollinated plant species are typically tubular, with an opening at only one end, and the pollen inside is smooth-grained and firmly attached. With self-fertile plants such as tomatoes, wind may be sufficient to shake loose the pollen through pores in the anther and accomplish pollination. Visits by bees may also shake loose some pollen, but more efficient pollination of those plants is accomplished by a few insect species who specialize in sonication or buzz pollination.

<span class="mw-page-title-main">Entomophily</span> Form of pollination by insects

Entomophily or insect pollination is a form of pollination whereby pollen of plants, especially but not only of flowering plants, is distributed by insects. Flowers pollinated by insects typically advertise themselves with bright colours, sometimes with conspicuous patterns leading to rewards of pollen and nectar; they may also have an attractive scent which in some cases mimics insect pheromones. Insect pollinators such as bees have adaptations for their role, such as lapping or sucking mouthparts to take in nectar, and in some species also pollen baskets on their hind legs. This required the coevolution of insects and flowering plants in the development of pollination behaviour by the insects and pollination mechanisms by the flowers, benefiting both groups. Both the size and the density of a population are known to affect pollination and subsequent reproductive performance.

<span class="mw-page-title-main">Zoophily</span> Pollination by animals

Zoophily, or zoogamy, is a form of pollination whereby pollen is transferred by animals, usually by invertebrates but in some cases vertebrates, particularly birds and bats, but also by other animals. Zoophilous species frequently have evolved mechanisms to make themselves more appealing to the particular type of pollinator, e.g. brightly colored or scented flowers, nectar, and appealing shapes and patterns. These plant-animal relationships are often mutually beneficial because of the food source provided in exchange for pollination.

<span class="mw-page-title-main">Nectar</span> Sugar-rich liquid produced by many flowering plants, that attracts pollinators and insects

Nectar is a sugar-rich liquid produced by plants in glands called nectaries or nectarines, either within the flowers with which it attracts pollinating animals, or by extrafloral nectaries, which provide a nutrient source to animal mutualists, which in turn provide herbivore protection. Common nectar-consuming pollinators include mosquitoes, hoverflies, wasps, bees, butterflies and moths, hummingbirds, honeyeaters and bats. Nectar plays a crucial role in the foraging economics and evolution of nectar-eating species; for example, nectar foraging behavior is largely responsible for the divergent evolution of the African honey bee, A. m. scutellata and the western honey bee.

<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.

<span class="mw-page-title-main">Nectarivore</span> Animal in which nectar is a main source of nutrition in their diet.

In zoology, a nectarivore is an animal which derives its energy and nutrient requirements from a diet consisting mainly or exclusively of the sugar-rich nectar produced by flowering plants.

<span class="mw-page-title-main">Ornithophily</span> Pollination by birds

Ornithophily or bird pollination is the pollination of flowering plants by birds. This sometimes coevolutionary association is derived from insect pollination (entomophily) and is particularly well developed in some parts of the world, especially in the tropics, Southern Africa, and on some island chains. The association involves several distinctive plant adaptations forming a "pollination syndrome". The plants typically have colourful, often red, flowers with long tubular structures holding ample nectar and orientations of the stamen and stigma that ensure contact with the pollinator. Birds involved in ornithophily tend to be specialist nectarivores with brushy tongues and long bills, that are either capable of hovering flight or light enough to perch on the flower structures.

<span class="mw-page-title-main">Palynivore</span> Group of herbivorous animals

In zoology, a palynivore /pəˈlɪnəvɔːɹ/, meaning "pollen eater" is an herbivorous animal which selectively eats the nutrient-rich pollen produced by angiosperms and gymnosperms. Most true palynivores are insects or mites. The category in its strictest application includes most bees, and a few kinds of wasps, as pollen is often the only solid food consumed by all life stages in these insects. However, the category can be extended to include more diverse species. For example, palynivorous mites and thrips typically feed on the liquid content of the pollen grains without actually consuming the exine, or the solid portion of the grain. Additionally, the list is expanded greatly if one takes into consideration species where either the larval or adult stage feeds on pollen, but not both. There are other wasps which are in this category, as well as many beetles, flies, butterflies, and moths. One such example of a bee species that only consumes pollen in its larval stage is the Apis mellifera carnica. There is a vast array of insects that will feed opportunistically on pollen, as will various birds, orb-weaving spiders and other nectarivores.

<span class="mw-page-title-main">Pollination syndrome</span> Flower traits that attract pollinators

Pollination syndromes are suites of flower traits that have evolved in response to natural selection imposed by different pollen vectors, which can be abiotic or biotic, such as birds, bees, flies, and so forth through a process called pollinator-mediated selection. These traits include flower shape, size, colour, odour, reward type and amount, nectar composition, timing of flowering, etc. For example, tubular red flowers with copious nectar often attract birds; foul smelling flowers attract carrion flies or beetles, etc.

<span class="mw-page-title-main">Nectar robbing</span> Foraging behavior

Nectar robbing is a foraging behavior utilized by some organisms that feed on floral nectar, carried out by feeding from holes bitten in flowers, rather than by entering through the flowers' natural openings. "Nectar robbers" usually feed in this way, avoiding contact with the floral reproductive structures, and therefore do not facilitate plant reproduction via pollination. Because many species that act as pollinators also act as nectar robbers, nectar robbing is considered to be a form of exploitation of plant-pollinator mutualism. While there is variation in the dependency on nectar for robber species, most species rob facultatively.

<span class="mw-page-title-main">Western honey bee</span> European honey bee

The western honey bee or European honey bee is the most common of the 7–12 species of honey bees worldwide. The genus name Apis is Latin for "bee", and mellifera is the Latin for "honey-bearing" or "honey carrying", referring to the species' production of honey.

<span class="mw-page-title-main">Flower constancy</span> Tendency to visit certain flower species

Flower constancy or pollinator constancy is the tendency of individual pollinators to exclusively visit certain flower species or morphs within a species, bypassing other available flower species that could potentially contain more nectar. This type of foraging behavior puts selective pressures on floral traits in a process called pollinator-mediated selection. Flower constancy is different from other types of insect specialization such as innate preferences for certain colors or flower types, or the tendency of pollinators to visit the most rewarding and abundant flowers.

<i>Trigona fuscipennis</i> Species of bee

Trigona fuscipennis is a stingless bee species that originates in Mexico but is also found in Central and South America. They are an advanced eusocial group of bees and play a key role as pollinators in wet rainforests. The species has many common names, including mapaitero, sanharó, abelha-brava, xnuk, k'uris-kab, enreda, corta-cabelo, currunchos, zagaño, and enredapelos.

<span class="mw-page-title-main">Monocotyledon reproduction</span> Flowering plant reproduction system

The monocots are one of the two major groups of flowering plants, the other being the dicots. In order to reproduce they utilize various strategies such as employing forms of asexual reproduction, restricting which individuals they are sexually compatible with, or influencing how they are pollinated. Nearly all reproductive strategies that evolved in the dicots have independently evolved in monocots as well. Despite these similarities and their close relatedness, monocots and dicots have distinct traits in their reproductive biologies.

<span class="mw-page-title-main">UV coloration in flowers</span> Natural phenomenon

UV coloration is a natural phenomenon that leads to unique interactions between organisms that have evolved the ability to perceive these wavelengths of light. It serves as one method to attract pollinators to the flower along with scent, shape, and nectar quality. Flowers are known for their range of visible colors that humans can see with their eyes and observe an array of different shades and patterns. The naked eye cannot see the ultraviolet coloration many flowers employ to bring attention to themselves. By either reflecting or absorbing UV light waves, flowers are able to communicate with pollinators. This allows plants that may require an animal pollinator to stand out from other flowers or distinguish where their flowers are in a muddied background of other plant parts. For the plant, it is important to share and receive pollen so they can reproduce, maintain their ecological role, and guide the evolutionary history of the population.

<i>Chalepogenus</i>

The genus Chalepogenus, consisting of 21 species of solitary oil-collecting apid bees, demonstrates oligolecty by foraging on oil-producing flowers from the families Calceolariaceae, Iridaceae and Solanaceae. These oil-flowers are abundant in South America, where Chalepogenus is endemic. In contrast to honey bees, Chalepogenus species do not collect nectar; instead, they gather floral oil for various purposes, including provisioning their larvae, constructing nests, and sustaining foraging adult bees. Although oil collection has been reported to be performed by females only, both males and females have specialised oil-collecting structures.

References

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