Termite (Order: Isoptera) - Wiki
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[Photo] Coptotermes formosanus shiraki; Formosan subterranean termites(en:Termite), イエシロアリ(ja:シロアリ). Formosan subterranean termite soldiers (red colored heads) and workers (pale colored heads). Source: USDA, ARS, IS Photo Unit'file (http://www.ars.usda.gov/is/graphics/photos/oct98/k8204-7.htm), "Formosan subterranean termites are feeding on Sudan-red-stained filter paper. Tracking the termites stained with this dye allows researchers to estimate their foraging range and population numbers.". Author Photo by Scott Bauer.
Termites, sometimes known as white ants, are a group of social insects usually classified at the taxonomic rank of order Isoptera. (This has been challenged by recent research, see taxonomy below.) Termites usually prefer to feed on dead plant material, generally in the form of wood, leaf litter, or soil, and about 10% of the 4,000 odd species (about 2,600 taxonomically known) are economically significant as pests that can cause serious structural damage to buildings, crops or plantation forests. Termites are major detrivores, particularly in the subtropical and tropical regions, and their recycling of wood and other plant matter is of considerable ecological importance.
As social insects, termites live in colonies that, at maturity, number from several hundred to several million individuals. They are a prime example of decentralised, self-organised systems using swarm intelligence and use this cooperation to exploit food sources and environments that could not be available to any single insect acting alone. A typical colony contains nymphs (semi-mature young), workers, soldiers, and reproductive individuals of both genders, sometimes containing several egg-laying queens.
A female that has flown, mated and is producing eggs, is called a "Queen". Similarly, a male that has flown, mated and remains in proximity to a queen, is termed a "King". These anthropocentric terms have caused great misunderstanding of colony dynamics. Research using genetic techniques to determine relatedness of colony members is showing that the idea that colonies are headed by a monogamous royal pair is at least sometimes incorrect. Multiple pairs of reproductives within a colony are not uncommon, but for the families Rhinotermitidae and Termitidae, at least, sperm competition does not seem to occur (male genitalia are very simple and the sperm are anucleate), suggesting that only one male (king) generally mates within the colony.
At maturity, a primary queen can lay several thousand eggs a day. In physogastric species, the queen adds an extra set of ovaries with each moult, resulting in a greatly distended abdomen and increased fecundity. The distended abdomen increases her size in some species to as much as 10 centimetres, hundreds of times the original size, effectively immobilizing her. In times where these huge queens must be moved to a new chamber it requires a group effort to move her and hundreds of workers are required to push her. The queen is widely believed to be a primary source of pheromones useful in colony integration. As a reward for attending workers a juice is secreted from the queen's posterior for the workers to drink.
The king remains only slightly bigger than an average termite and continues to mate with the queen for life. This is very different from ant societies, which have colonies with only a queen which mates once with the male(s) and stores his gametes for life. Males in ant colonies die immediately after mating, unlike termite male alates, which become kings and live with the queen.
The alate caste, also referred to as the reproductive caste, are generally the only termites with well-developed eyes (although workers of some harvesting species do have well-developed compound eyes and in other species soldiers with eyes occasionally appear). Immature alates still going through incomplete metamorphosis form a sub-caste in certain species of termites, functioning as functional workers ('pseudergates') and also as potential supplementary reproductives. Supplementaries have the ability to replace a dead primary reproductive and in at least some species several are recruited once a primary queen is lost.
In areas with a distinct dry season, the alates leave the nest in large swarms after the first good soaking rain of the rainy season. They are relatively poor flyers and are blown downwind, shedding their wings as soon as they land, where they mate and attempt to form a nest in the damp earth.
Worker termites undertake the labours of foraging, food storage, brood, nest maintenance and some of the defense effort in certain species. Workers are the main caste in the colony for the digestion of cellulose in food. This is achieved in one of two ways. In all termite families except the Termitidae, there are flagellates (Protista) in the gut that assist in cellulose digestion. However, in the Termitidae, which account for approximately 60% of all termite species, the flagellates have been lost and this digestive role is taken up, in part, by a consortium of prokaryotic organisms. This simple story, which has been in Entomology textbooks for decades, is complicated by the finding that all studied termites can produce their own cellulase enzymes, and therefore can digest wood in the absence of their symbiotic microbes. Our knowledge of the relationships between the microbial and termite parts of their digestion is still rudimentary. What is true in all termite species, however, is that the workers feed the other members of the colony with substances derived from the digestion of plant material, either from the mouth or anus This process of feeding of one colony member by another is known as trophallaxis, and is one of the keys to the success of the group as it frees the parents from feeding the young, allowing for the group to grow much larger and ensuring that the gut symbionts are transferred from one generation to another.
Termite workers are generally blind due to undeveloped eyes. Despite this limitation they are able to create elaborate nests and tunnel systems using a combination of soil, chewed wood /cellulose, saliva and faeces. Some species have been known to create such durable walls that industrial machinery has been damaged in an attempt to break their tall mounds. Some African and Australian species have mounds more than 4 metres high. The nest is created and maintained by workers with many distinct features such as housing the brood, water collection through condensation, reproductive chambers, and tunnel networks that effectively provide air conditioning. A few species even practice agriculture, collecting plant matter to feed fungal gardens, upon which the colony then feeds.
The soldier caste has anatomical and behavioural specializations, primarily useful against ant attack. The proportion of soldiers within a colony varies both within and between species. Many soldiers have jaws so enlarged that they cannot feed themselves, but instead, like juveniles, are fed by workers. The pan-tropical sub family Nasutitermitinae (which should probably have the South American species separated) have soldiers with the ability to exude noxious liquids through either a horn-like nozzle (nasus) or simple hole in the head (fontanelle). Fontanelles which exude defensive secretions are also a feature of the family Rhinotermitidae. Many species are readily identified using the characteristics of the soldiers' heads, mandibles, or nasus. Among the drywood termites, a soldier's globular ("phragmotic") head can be used to block their narrow tunnels. Termite soldiers are usually blind, but in some families, soldiers developing from the reproductive line have at least partly functional eyes.
It's generally accepted that the specialization of the soldier caste is principally a defense against predation by ants. The wide range of jaw types and phragmotic heads provides methods which effectively block narrow termite tunnels against ant entry. A tunnel-blocking soldier can rebuff attacks from many ants. Usually more soldiers stand by behind the initial soldier so once the first one falls another soldier will take the place. In cases where the intrusion is coming from a breach that is larger than the soldier's head, defense requires special formations where soldiers form a phalanx-like formation around the breach blindly biting at intruders or shooting toxic glue from the nasus. This formation involves self sacrifice because once the workers have repaired the breach during fighting no return is provided, causing the death of all the defenders.
Termites undergo incomplete metamorphosis, with their freshly hatched young taking the form of tiny termites that grow without significant morphological changes. Some species of termite have been known to have small groups of extremely large soldiers (3*normal size). Though their value is unknown speculation indicates that they may function as an elite class that defends only the inner tunnels of the mound. Evidence for this is that, even when provoked, these large soldiers do not defend themselves but retreat deeper into the mound. Some termite taxa do not have any soldiers; perhaps the best known of these is the Apicotermitinae.
Termites are generally grouped according to their feeding behaviour. Thus the commonly used general groupings are: Subterranean, Soil-feeding, Drywood, Dampwood and Grass eating. Of these, subterraneans and drywoods are primarily responsible for damage to human structures.
All termites eat cellulose in its various forms as plant fiber. Cellulose is a rich energy source (think of the amount of energy released when wood is burned), but remains difficult to digest. Termites rely primarily upon symbiotic protozoa (metamonads) such as Trichonympha, and other microbes in their gut to digest the cellulose for them, absorbing the end products for their own use. Gut protozoa such as Trichonympha, in turn rely on symbiotic bacteria embedded on their surfaces to produce some of the necessary digestive enzymes. This relationship is one of the finest examples of mutualism among animals. Most so called "higher termites", especially in the Family Termitidae can produce their own cellulase enzymes. However, they still retain a rich gut fauna with bacteria dominant. Due to closely related bacterial species, it is strongly presumed that the termites' gut flora are descended from the gut flora of the ancestral wood-eating cockroachs, like those of the genus Cryptocercus.
Some species of termite practice fungiculture - they maintain a 'garden' of specialized fungi of genus Termitomyces, which are nourished by the excrement of the insects. When the fungi in turn are eaten, their spores pass undamaged through the intestines of the termites, to complete the cycle by germinating in the fresh faecal pellets.
Termites build nests to house their colonies, in growing trees, inside fallen trees, underground, and in above-ground mounds which they construct, commonly called "anthills" in Africa and Australia, despite the technical incorrectness of that name. In tropical savannas the mounds may be very large, with an extreme of 9 metres (30 ft) high in the case of large conical mounds constructed by some Macrotermes species in well-wooded areas in Africa, though 2???3 m would be typical for the largest mounds in most savannas. The shape ranges form somewhat amorphous domes or cones usually covered in grass and/or woody shrubs, to sculptured hard earth mounds, or a mixture of the two.
The sculptured mounds sometimes have elaborate and distinctive forms, such as those of the compass termite (Amitermes meridionalis & A. laurensis) which build tall wedge-shaped mounds with the long axis oriented approximately north-south. This orientation has been experimentally shown to help in thermoregulation.
The column of hot air rising in the above ground mounds helps drive air circulation currents inside the subterranean network. The structure of these mounds can be quite complex. The temperature control is essential for those species that cultivate fungal gardens and even for those that don't, much effort and energy is spent maintaining the brood within a narrow temperature range, often only plus or minus one degree C over a day.
In some parts of the African savanna a high density of above-ground mounds dominates the landscape. For instance in some parts of the Busanga Plain area of Zambia, small mounds of about 1 m diameter with a density of about 100 per hectare can be seen on grassland between larger tree- and bush-covered mounds about 25 m in diameter with a density around 1 per hectare, and both show up well on high-resolution satellite images taken in the wet season.
Recent DNA evidence has supported the nearly 120 year-old hypothesis, originally based on morphology, that termites are most closely related to the species of wood-eating cockroaches (genus Cryptocercus). Most recently this has led some authors to propose that termites be reclassified as a single family, Termitidae, within the order Blattodea, which contains cockroaches. However, most researchers advocate the less drastic measure of retaining the termites as Isoptera but as a group subordinate to true roaches, preserving the internal classification of termites.
As of 1996, about 2,800 are recognized, classified in seven families:
Termopsidae (5 genera, 20 species)
Hodotermitidae (3 genera, 19 species)
Mastotermitidae (1 species, Mastotermes darwiniensis)
Kalotermitidae (22 genera, 419 species)
Rhinotermitidae (14 genera, 343 species)
Prorhinoterminae Quennedey & Deligne, 1975
Stylotermitinae Holmgren, K & N, 1917
Serritermitidae (1 species, Serritermes serrifer)
Termitidae (236 genera, 1958 species)
Macrotermitinae (14 genera, 349 species)
Nasutitermitinae (91 genera, 663 species)
Amitermitinae (17 genera, 295 species)
Apicotermitinae (43 genera, 202 species)
Cubitermitinae (28 genera, 161 species)
Termitinae (43 genera, 288 species)
The most current classification of termites is summarized by Engel & Krishna (2004).
Termites as a source of power
One of the US Department of Energy's most enduring goals is to replace fossil fuels with renewable sources of cleaner energy, such as hydrogen produced from plant biomass fermentation. Termites may help reach this goal through metagenomics.
Termites are capable of producing up to two liters of hydrogen from fermenting a single sheet of paper, making them one of the planet's most efficient bioreactors. Termites achieve this high degree of efficiency by exploiting the metabolic capabilities of about 200 different species of microbes that inhabit their hindguts.
Hydrogen is normally created by using electricity to remove hydrogen molecules from water or natural gas, but the electricity is most often generated using fossil fuels that emit carbon pollutants. The microbial community in the termite gut efficiently manufactures large quantities of clean hydrogen. By sequencing the termite's microbial community, it may be possible to get a better understanding of these biochemical pathways.
Termites eat wood, but cannot extract energy from the complex lignocellulose polymers within it. These polymers are broken down into simple sugars by fermenting bacteria in the termite's gut, using enzymes that produce hydrogen as a byproduct. A second wave of bacteria uses the simple sugars and hydrogen to make the acetate the termite requires for energy. If it can be figured out which enzymes are used to create hydrogen, and which genes produce them, this process could be scaled up with bioreactors to generate hydrogen from woody biomass, such as poplar, in commercial quantities.
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