Pollination syndrome - AbsoluteAstronomy.com

Pollination syndromes are suites of flower

Flower

A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...

traits that have evolved in response to natural selection

Natural selection

Natural selection is the nonrandom process by which biologic traits become either more or less common in a population as a function of differential reproduction of their bearers. It is a key mechanism of evolution....

imposed by different pollen vectors, which can be abiotic (wind and water) or biotic, such as birds, bees, flies, and so forth. 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.

The "classical" pollination syndromes as they are currently defined (see below) were developed in the 19th Century by the Italian botanist Federico Delpino

Federico Delpino

Frederico Delpino was an Italian botanist who made very important observations on the pollination of flowers by insects...

. Although they have been useful in developing our understanding of plant-pollinator interactions, an uncritical acceptance of pollination syndromes as providing a framework for classifying these relationships is rather out of date.

Abiotic pollination syndromes

These do not attract animal pollinators. Nevertheless, they often have suites of shared traits.

Wind pollination (anemophily)

Flowers may be small and inconspicuous, green and not showy. They produce enormous numbers of relatively small pollen

Pollen

Pollen is a fine to coarse powder containing the microgametophytes of seed plants, which produce the male gametes . Pollen grains have a hard coat that protects the sperm cells during the process of their movement from the stamens to the pistil of flowering plants or from the male cone to the...

grains (hence wind-pollinated plants may be allergen

Allergen

An allergen is any substance that can cause an allergy. In technical terms, an allergen is a non-parasitic antigen capable of stimulating a type-I hypersensitivity reaction in atopic individuals....

s, but seldom are animal-pollinated plants allergenic). Their stigmas may be large and feathery to catch the pollen grains. Insects may visit them to collect pollen; in some cases these are ineffective pollinators and exert little natural selection on the flowers, but there are also examples of ambophilous flowers which are both wind and insect pollinated.
Anaemophilous or wind pollinated flowers should be usually small,inconspicuos.uattractive.They do not produce scent or nectar but the anther produce a large number of pollen grains,the stamens are long and protrude out of flower.

Water pollination (hydrophily)

Water-pollinated plants are aquatic

Aquatic plant

Aquatic plants are plants that have adapted to living in aquatic environments. They are also referred to as hydrophytes or aquatic macrophytes. These plants require special adaptations for living submerged in water, or at the water's surface. Aquatic plants can only grow in water or in soil that is...

and pollen is released into the water. Water currents therefore act as a pollen vector in a similar way to wind currents. Their flowers tend to be small and inconspicuous with lots of pollen grains and large, feathery stigmas to catch the pollen. However, this is relatively uncommon (only 2% of pollination is Hydrophily) and most aquatic plants are insect-pollinated, with flowers that emerge into the air.

Biotic pollination syndromes

Bee pollination (melittophily)

Bee

Bees are flying insects closely related to wasps and ants, and are known for their role in pollination and for producing honey and beeswax. Bees are a monophyletic lineage within the superfamily Apoidea, presently classified by the unranked taxon name Anthophila...

-pollinated flowers can be very variable in their size, shape and colouration. They can be open and bowl-shaped (radially symmetrical) or more complex and non-radially symmetric ("zygomorphic") such as many pea

Pea

A pea is most commonly the small spherical seed or the seed-pod of the pod fruit Pisum sativum. Each pod contains several peas. Peapods are botanically a fruit, since they contain seeds developed from the ovary of a flower. However, peas are considered to be a vegetable in cooking...

s, foxgloves, etc.

Some bee flowers tend to be yellow or blue, often with ultraviolet nectar guide

Nectar guide

Nectar guides are patterns seen in some species of flowers, guiding pollinators to their rewards. Rewards commonly take the form of nectar, pollen, or both, but various plants produce oil, resins, scents, or waxes...

s and scent. Nectar, pollen, or both are offered as rewards in varying amounts. The sugar in the nectar tends to be sucrose

Sucrose

Sucrose is the organic compound commonly known as table sugar and sometimes called saccharose. A white, odorless, crystalline powder with a sweet taste, it is best known for its role in human nutrition. The molecule is a disaccharide composed of glucose and fructose with the molecular formula...

-dominated.

There are diverse types of bees, however. Honeybees, bumblebee

Bumblebee

A bumble bee is any member of the bee genus Bombus, in the family Apidae. There are over 250 known species, existing primarily in the Northern Hemisphere although they are common in New Zealand and in the Australian state of Tasmania.Bumble bees are social insects that are characterised by black...

s, orchid bees, etc. are large groups that are quite distinctive in size, tongue

Tongue

The tongue is a muscular hydrostat on the floors of the mouths of most vertebrates which manipulates food for mastication. It is the primary organ of taste , as much of the upper surface of the tongue is covered in papillae and taste buds. It is sensitive and kept moist by saliva, and is richly...

length and behaviour (some solitary, some colonial). Thus generalization about bees is difficult. Some plants can only be pollinated by bees because their anthers release pollen internally, and it must be shaken out by buzz pollination

Buzz pollination

Sonication or buzz pollination is a technique used by some bees to release pollen which is more or less firmly held by the anthers, which makes pollination more efficient. The anther of buzz-pollinated species of plants is typically tubular, with an opening at only one end, and the pollen is inside...

(also known as "sonication"). Bees are the only animals that perform this behaviour. Bumblebees sonicate, but honeybees do not.

Bee pollination from mobile beehives is of great economic value for orchards such as apple

Apple

The apple is the pomaceous fruit of the apple tree, species Malus domestica in the rose family . It is one of the most widely cultivated tree fruits, and the most widely known of the many members of genus Malus that are used by humans. Apple grow on small, deciduous trees that blossom in the spring...

or almond

Almond

The almond , is a species of tree native to the Middle East and South Asia. Almond is also the name of the edible and widely cultivated seed of this tree...

Wasp pollination

Wasps are also responsible for the pollination of several plants species, being important pollen vectors and, in some cases, efficient pollinators even more than bees.

Butterfly pollination (psychophily)

Butterfly

A butterfly is a mainly day-flying insect of the order Lepidoptera, which includes the butterflies and moths. Like other holometabolous insects, the butterfly's life cycle consists of four parts: egg, larva, pupa and adult. Most species are diurnal. Butterflies have large, often brightly coloured...

-pollinated flowers tend to be large and showy, pink or lavender in colour, frequently have a landing area, and are usually scented. Since butterflies do not digest

Digestion

Digestion is the mechanical and chemical breakdown of food into smaller components that are more easily absorbed into a blood stream, for instance. Digestion is a form of catabolism: a breakdown of large food molecules to smaller ones....

pollen (with one exception), more nectar is offered than pollen. The flowers have simple nectar guides with the nectaries usually hidden in narrow tubes or spurs, reached by the long tongue of the butterflies.

Moth pollination (phalaenophily)

Among the more important moth

Moth

A moth is an insect closely related to the butterfly, both being of the order Lepidoptera. Moths form the majority of this order; there are thought to be 150,000 to 250,000 different species of moth , with thousands of species yet to be described...

pollinators are the hawk moths (Sphingidae

Sphingidae

Sphingidae is a family of moths , commonly known as hawk moths, sphinx moths and hornworms, that includes about 1,200 species . It is best represented in the tropics but there are species in every region . They are moderate to large in size and are distinguished among moths for their rapid,...

). Their behaviour is similar to hummingbird

Hummingbird

Hummingbirds are birds that comprise the family Trochilidae. They are among the smallest of birds, most species measuring in the 7.5–13 cm range. Indeed, the smallest extant bird species is a hummingbird, the 5-cm Bee Hummingbird. They can hover in mid-air by rapidly flapping their wings...

s: they hover in front of flowers with rapid wingbeats. Most are nocturnal or crepuscular

Crepuscular

Crepuscular animals are those that are active primarily during twilight, that is during dawn and dusk. The word is derived from the Latin word crepusculum, meaning "twilight." Crepuscular is, thus, in contrast with diurnal and nocturnal behavior. Crepuscular animals may also be active on a bright...

. So moth-pollinated flowers tend to be white, night-opening, large and showy with tubular corolla

Petal

Petals are modified leaves that surround the reproductive parts of flowers. They often are brightly colored or unusually shaped to attract pollinators. Together, all of the petals of a flower are called a corolla. Petals are usually accompanied by another set of special leaves called sepals lying...

s and a strong, sweet scent produced in the evening, night or early morning. A lot of nectar is produced to fuel the high metabolic rates needed to power their flight.

Other moths (Noctuids, Geometrids, Pyralids, for example) fly slowly and settle on the flower. They do not require as much nectar as the fast-flying hawk moths, and the flowers tend to be small (though they may be aggregated in heads).

Fly pollination (myophily and sapromyophily)

The classical syndromes recognise two types of fly pollination: myophily and sapromyophily. Some flies feed on nectar and pollen as adults (particularly bee flies (Bombyliidae), hoverflies

Hoverfly

Hoverflies, sometimes called flower flies or syrphid flies, make up the insect family Syrphidae. As their common name suggests, they are often seen hovering or nectaring at flowers; the adults of many species feed mainly on nectar and pollen, while the larvae eat a wide range of foods...

(Syrphidae), etc.). Those regularly visit flowers. On the other hand, male fruit flies

Tephritidae

Tephritidae is one of two fly families referred to as "fruit flies", the other family being Drosophilidae. Tephritidae does not include the biological model organisms of the genus Drosophila , which is often called the "common fruit fly". There are nearly 5,000 described species of tephritid...

(Tephritidae) are attracted to and feed on specific floral attractant, which acts as fly's sex pheromone precursor or booster, of some wild orchids (Bulbophyllum species - with highly moveable lip) that do not produce nectar. These are the myophiles. Sapromyophiles, on the other hand, normally visit dead animals or dung

Feces

Feces, faeces, or fæces is a waste product from an animal's digestive tract expelled through the anus or cloaca during defecation.-Etymology:...

. They are attracted to flowers that mimic these odoriferous items. They obtain no reward and would quickly leave, but the plant may have traps to slow them down. These plants have a strong, unpleasant odor, and are brown or orange in color. They are not as common as myophilous plants. Myophilous plants do not tend to have a strong scent, and tend to be purple, violet, blue, and white, open dishes, or tubes. Although they have traditionally been considered to be ineffective and unreliable pollinators, their sheer numbers and the presence of some flies throughout the year make them important pollinators for many plants.

Flies tend to be important pollinators in high-altitude

Altitude

Altitude or height is defined based on the context in which it is used . As a general definition, altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The reference datum also often varies according to the context...

and high-latitude

Latitude

In geography, the latitude of a location on the Earth is the angular distance of that location south or north of the Equator. The latitude is an angle, and is usually measured in degrees . The equator has a latitude of 0°, the North pole has a latitude of 90° north , and the South pole has a...

systems, where they are numerous and other insect groups may be lacking.

Bird pollination (ornithophily)

Although hummingbirds are the most familiar nectar-feeding bird

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s for North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

ns, there are analogous species in other parts of the world: sunbird

Sunbird

The sunbirds and spiderhunters are a family, Nectariniidae, of very small passerine birds. There are 132 species in 15 genera. The family is distributed throughout Africa, southern Asia and just reaches northern Australia. Most sunbirds feed largely on nectar, but also take insects and spiders,...

s, honeyeater

Honeyeater

The honeyeaters are a large and diverse family of small to medium sized birds most common in Australia and New Guinea, but also found in New Zealand, the Pacific islands as far east as Samoa and Tonga, and the islands to the north and west of New Guinea known as Wallacea...

s, flowerpecker

Flowerpecker

The flowerpeckers are a family, Dicaeidae , of passerine birds. The family comprises two genera, Prionochilus and Dicaeum, with 44 species in total. The family has sometimes been included in an enlarged sunbird family Nectariniidae. The berrypeckers of the family Melanocharitidae and the painted...

s, honeycreeper

Honeycreeper

The typical honeycreepers are small birds in the tanager family. They are found in the tropical New World from Mexico south to Brazil.They occur in the forest canopy, and, as the name implies, they are specialist nectar feeders with long curved bills....

s, bananaquit

Bananaquit

The Bananaquit is a species of passerine bird of uncertain relation. It is tentatively placed in the tanager family, but classified as incertae sedis by other authorities such as the American Ornithologists' Union. Its classification is debated, and it is often placed in its own family: Coerebidae...

s, flowerpiercer

Diglossa (bird)

Diglossa is a genus of flowerpiercers in the family Thraupidae. Sometimes classified in the bunting and American sparrow family Emberizidae, more recent studies have shown it to belong in the Thraupidae...

s, lories and lorikeets. Hummingbirds are the oldest group, with the greatest degree of specialization on nectar. Flowers attractive to hummingbirds that can hover in front of the flower tend to be large red or orange tubes with a lot of dilute nectar, secreted during the day. Since birds do not have a strong response to scent, they tend to be odorless. Perching birds need a substantial landing platform, so sunbirds, honeyeaters, and the like are less associated with tubular flowers.

Bat pollination (chiropterophily)

Bat

Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, glide rather than fly,...

-pollinated flowers tend to be large and showy, white or light coloured, open at night and have strong odours. They are often large and bell

Bell (instrument)

A bell is a simple sound-making device. The bell is a percussion instrument and an idiophone. Its form is usually a hollow, cup-shaped object, which resonates upon being struck...

-shaped. Bats drink the nectar, and these plants typically offer nectar for extended periods of time. Sight, smell, and echo-location

Animal echolocation

Echolocation, also called biosonar, is the biological sonar used by several kinds of animals.Echolocating animals emit calls out to the environment and listen to the echoes of those calls that return from various objects near them. They use these echoes to locate and identify the objects...

are used to initially find the flowers, and excellent spatial memory is used to visit them repeatedly. In fact, bats can identify nectar-producing flowers using echolocation. In the New World

New World

The New World is one of the names used for the Western Hemisphere, specifically America and sometimes Oceania . The term originated in the late 15th century, when America had been recently discovered by European explorers, expanding the geographical horizon of the people of the European middle...

, bat pollinated flowers often have sulfur

Sulfur

Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

-scented compounds, but this does not carry to other parts of the world. Bat-pollinated plants have bigger pollen than their relatives.

Beetle pollination (cantharophily)

Beetle

Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...

-pollinated flowers are usually large, greenish or off-white in color and heavily scented. Scents may be spicy, fruity, or similar to decaying organic material. Most beetle-pollinated flowers are flattened or dish shaped, with pollen easily accessible, although they may include traps to keep the beetle longer. The plant's ovaries are usually well protected from the biting mouthparts of their pollinators. Beetles may be particularly important in some parts of the world such as semi-arid areas of southern Africa

Southern Africa

Southern Africa is the southernmost region of the African continent, variably defined by geography or geopolitics. Within the region are numerous territories, including the Republic of South Africa ; nowadays, the simpler term South Africa is generally reserved for the country in English.-UN...

and southern California

Southern California

Southern California is a megaregion, or megapolitan area, in the southern area of the U.S. state of California. Large urban areas include Greater Los Angeles and Greater San Diego. The urban area stretches along the coast from Ventura through the Southland and Inland Empire to San Diego...

and the montane grasslands of KwaZulu-Natal

KwaZulu-Natal

KwaZulu-Natal is a province of South Africa. Prior to 1994, the territory now known as KwaZulu-Natal was made up of the province of Natal and the homeland of KwaZulu....

in South Africa

South Africa

The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...

Biology

Pollination syndromes reflect convergent evolution

Convergent evolution

Convergent evolution describes the acquisition of the same biological trait in unrelated lineages.The wing is a classic example of convergent evolution in action. Although their last common ancestor did not have wings, both birds and bats do, and are capable of powered flight. The wings are...

towards forms (phenotype

Phenotype

A phenotype is an organism's observable characteristics or traits: such as its morphology, development, biochemical or physiological properties, behavior, and products of behavior...

s) that limit the number of species of pollinator

Pollinator

A pollinator is the biotic agent that moves pollen from the male anthers of a flower to the female stigma of a flower to accomplish fertilization or syngamy of the female gamete in the ovule of the flower by the male gamete from the pollen grain...

s visiting the plant. They increase the functional specialization of the plant with regard to pollination, though this may not affect the ecological specialization (i.e. the number of species of pollinators within that functional group). They are responses to common selection pressures exerted by shared pollinators or abiotic pollen vectors, which generate correlations among traits. That is, if two distantly related plant species are both pollinated by nocturnal moths, for example, their flowers will converge on a form which is recognised by the moths (e.g. pale colour, sweet scent, nectar released at the base of a long tube, night-flowering).

Advantages of specialization

Efficiency of pollination: the rewards given to pollinators (commonly nectar or pollen or both, but sometimes oil, scents, resins, or wax) may be costly to produce. Nectar can be cheap, but pollen is generally expensive as it is relatively high in nitrogen compounds. Plants have evolved to obtain the maximum pollen transfer for the minimum reward. Different pollinators, because of their size, shape, or behaviour, have different efficiencies of transfer of pollen. And the floral traits affect efficiency of transfer: columbine
Aquilegia
Aquilegia is a genus of about 60-70 species of perennial plants that are found in meadows, woodlands, and at higher altitudes throughout the Northern Hemisphere, known for the spurred petals of their flowers.-Etymology:The genus name Aquilegia is derived from the Latin word for eagle , because...

flowers were experimentally altered and presented to hawkmoths, and flower orientation, shape, and colour were found to affect visitation rates or pollen removal.

Pollinator Constancy
Flower constancy
Flower constancy or pollinator constancy is defined as the tendency of individual pollinators to exclusively visit certain flower species or morphs within a species, bypassing other available flower species that could potentially be more rewarding...

: to efficiently transfer pollen, it is best for the plant if the pollinator focuses on one species of plant, ignoring other species. Otherwise, pollen may be dropped uselessly on the stigmas of other species. Animals, of course, do not aim to pollinate, they aim to collect food as fast as they can. However, many pollinator species exhibit constancy, passing up available flowers to focus on one plant species. Why should animals specialize on a plant species, rather than move to the next flower of any species? Although pollinator constancy was recognized by Aristotle
Aristotle
Aristotle was a Greek philosopher and polymath, a student of Plato and teacher of Alexander the Great. His writings cover many subjects, including physics, metaphysics, poetry, theater, music, logic, rhetoric, linguistics, politics, government, ethics, biology, and zoology...

, the benefits to animals are not yet fully understood. The most common hypothesis is that pollinators must learn to handle particular types of flowers, and they have limited capacity to learn different types. They can only efficiently gather rewards from one type of flower.

Pollinator constancy: these honeybees selectively visit flowers from only one species, as can be seen by the colour of the pollen in their baskets:

Advantages of generalization

Pollinators fluctuate in abundance and activity independently of their plants, and any one species may fail to pollinate a plant in a particular year. Thus a plant may be at an advantage if it attracts several species or types of pollinators, ensuring pollen transfer every year. Plants do, in many species, have the back-up option of self-pollination

Self-pollination

Self-pollination is a form of pollination that can occur when a flower has both stamen and a carpel in which the cultivar or species is self fertile and the stamens and the sticky stigma of the carpel contact each other in order to accomplish pollination...

, if they are not self-incompatible.

Criticisms of the syndromes

Whilst it is clear that pollination syndromes can be observed in nature, there has been much debate amongst scientists as to how frequent they are and to what extent we can use the classical syndromes to classify plant-pollinator interactions. Although some species of plants are visited only by one type of animal (i.e. they are functionally specialized), many plant species are visited by very different pollinators. For example, a flower may be pollinated by bees, butterflies, and birds. Strict specialization of plants relying on one species of pollinator is relatively rare, probably because it can result in variable reproductive success across years as pollinator populations vary significantly. In such cases, plants should generalize on a wide range of pollinators, and such ecological generalization is frequently found in nature. A study in Tasmania found the syndromes did not usefully predict the pollinators.

This debate has led to a critical re-evaluation of the syndromes, which suggests that on average about one third of the flowering plants can be classified into the classical syndromes. This reflects the fact that nature is much less predictable and straightforward than 19th Century biologists originally thought. Pollination syndromes can be thought of as extremes of a continuum of greater or lesser specialization or generalization onto particular functional groups of pollinators that exert similar selective pressures” and the frequency with which flowers conform to the expectations of the pollination syndromes is relatively rare. In addition, new types of plant-pollinator interaction, involving "unusual" pollinating animals are regularly being discovered, such as specialized pollination by spider hunting wasps (Pompilidae) and fruit chafers (Cetoniidae) in the eastern grasslands of South Africa. These plants do not fit into the classical syndromes, though they may show evidence of convergent evolution in their own right.

An analysis of flower traits and visitation in 49 species in the plant genus Penstemon
Penstemon
Penstemon , Beard-tongue, is a large genus of North American and East Asian plants traditionally placed in the Scrophulariaceae family. Due to new genetic research, it has now been placed in the vastly expanded family Plantaginaceae...

found that it was possible to separate bird- and bee- pollinated species quite well, but only by using floral traits which were not considered in the classical accounts of syndromes, such as the details of anther opening. Although a recent review concluded that there is “overwhelming evidence that functional groups exert different selection pressures on floral traits”, the sheer complexity and subtlety of plant-pollinator interactions (and the growing recognition that non-pollinating organisms such as seed predators can affect the evolution of flower traits) means that this debate is likely to continue for some time.