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Springtails (class Collembola) form the largest of the three lineages of modern Hexapoda that are no longer considered , i.e. Protura, Diplura and Collembola. Although the three lineages are sometimes grouped together in a class called Entognatha because they have internal mouthparts, they do not appear to be any more closely related to one another than they are to insects, which have external mouthparts. There are more than 9000 species.
Springtails are omnivorous, free-living organisms that prefer moist conditions. They do not directly engage in the decomposition of organic matter, but contribute to it indirectly through the fragmentation of organic matter and the control of soil microbial communities. The word Collembola is from the Ancient Greek κόλλα meaning 'glue' and ἔμβολος meaning 'peg'; this name was given due to the existence of the collophore, which was previously thought to stick to surfaces to stabilize the creature.
Early DNA sequence studies suggested that Collembola represent a separate evolutionary line from the other Hexapoda, but others disagree; this seems to be caused by widely divergent patterns of molecular evolution among the . The adjustments of traditional taxonomic rank for springtails reflect the occasional incompatibility of traditional groupings with modern cladistics: when they were included with the Insect, they were ranked as an order; as part of the Entognatha, they are ranked as a subclass. If they are considered within Hexapoda, they are elevated to full class status.
Springtails also possess the ability to reduce their body size by as much as 30% through subsequent ecdyses (moulting) if temperatures rise high enough. The shrinkage is genetically controlled. Since warmer conditions increase metabolic rates and energy requirements in organisms, the reduction in body size is advantageous to their survival.
The Poduromorpha and Entomobryomorpha have an elongated body, while the Symphypleona and Neelipleona have a globular body. Collembola lack a tracheal respiration system, which forces them to respire through a porous cuticle, except for the two families Sminthuridae and Actaletidae, which exhibit a single pair of spiracles between the head and the thorax, leading to a rudimentary, although fully functional, tracheal system. The anatomical variance (life-form variation) present between different species partially depends on their vertical distribution across the various strata of terrestrial . Surface-dwellers are generally larger, have darker pigments, longer antennae and a functioning furcula. Sub-surface-dwellers are usually unpigmented, have elongated bodies, and reduced furcula. They can be categorized into four main forms according to vertical distribution: atmobiotic, epedaphic, hemiedaphic, and euedaphic. Atmobiotic species inhabit macrophytes and litter surface. They are generally 8-10 millimeters (about ⅓ in) in length, pigmented, have long limbs, and a full set of ocelli (photoreceptors). Epedaphic species inhabit upper litter layers and fallen logs. They are slightly smaller and have less pronounced pigments, as well as less developed limbs and ocelli than the atmobiotic species. Hemiedaphic species inhabit the lower litter layers of decomposing organic material. They are 1-2 millimeters (about 1/16 in) in length, have dispersed pigmentation, shortened limbs, and a reduced number of ocelli. Euedaphic species inhabit upper mineral layers known as the humus horizon (or humipedon). They are smaller than hemiedaphic species; have soft, elongated bodies; lack pigmentation and ocelli; and have reduced or absent furca. (2026). 9780124159556 ISBN 9780124159556
Poduromorphs are characterized by their elongated bodies and conspicuous segmentation: they have three thoracic segments, six abdominal segments, including a well-developed prothorax with tergite , while the first thoracic segment in Entomobryomorpha is clearly reduced and bears no chaetae.
The digestive tract of springtails consists of three main components: foregut, midgut, and hindgut. The midgut is surrounded by a network of muscles and lined with a monolayer of columnar or cuboidal cells. Its function is to mix and transport food from the lumen into the hindgut through contraction. Many species of Syntrophy bacteria, archaea, and Fungus are present in the lumen. These different digestive regions have varying pH to support specific enzymatic activities and microbial populations. The anterior portion of the midgut and hindgut is slightly acidic (with a pH of approximately 6.0) while the posterior midgut portion is slightly alkaline (with a pH of approximately 8.0). Between the midgut and hindgut is an alimentary canal called the Pylorus region, which is a muscular sphincter. Malpighian tubules are absent.
The term Neopleona is essentially synonymous with Symphypleona + Neelipleona. The Neelipleona was originally seen as a particularly advanced lineage of Symphypleona, based on the shared global body shape, but the global body of the Neelipleona is realized in a completely different way than in Symphypleona. Subsequently, the Neelipleona were considered as being derived from the Entomobryomorpha. Analysis of 18S and 28S rRNA DNA sequence data, though, suggests that they form the most ancient lineage of springtails, which would explain their peculiar apomorphy. This phylogenetic relationship was also confirmed using a phylogeny based on mtDNA and Phylogenomics.
The latest whole-genome phylogeny supporting four orders of Collembola:
Springtails are attested to since the Early Devonian. The fossil from , Rhyniella praecursor, is the oldest terrestrial arthropod, and was found in the famous Rhynie chert of Scotland. Given its morphology resembles extant species quite closely, the radiation of the Hexapoda can be situated in the Silurian, or more. Additional research concerning the Coprolite (fossilized feces) of ancient springtails allowed researchers to track their lineages back some 412 million years.
Fossil Collembola are rare. Instead, most are found in amber. Even these are rare and many amber deposits carry few or no Collembola. The best deposits are from the early Eocene of Canada and Europe, Miocene of Central America, and the mid-Cretaceous of Burma and Canada. They display some unexplained characteristics: first, all but one of the fossils from the Cretaceous belong to extinct genera, whereas none of the specimens from the Eocene or the Miocene are of extinct genera; second, the species from Burma are more similar to the modern fauna of Canada than are the Canadian Cretaceous specimens.
There are now about 8,000 described species of Collembola. However, to the light of ongoing developments in molecular methods and the rise of cryptic species unveiled by DNA barcoding within morphologically-described species, it has been speculated that the global species richness of Collembola could be at least an order of magnitude greater than a previous estimate of 50,000 species.
Cave-dwelling springtails are a food source for and Opiliones in the same environment, such as the endangered harvestman Texella reyesi.
Predators also include various Geophilomorpha.
Jumping, using the furcula as a spring, is the most common way to avoid predation, but jump escape cannot be performed easily in concealed environments such as litter, and more especially soil layers. To protect themselves against predators, some species without jumping abilities have evolved chemical defenses.
In sheer numbers, they are reputed to be one of the most abundant of all macroscopic animals, with estimates of 100,000 individuals per square meter of ground, essentially everywhere on Earth where soil and related habitats (moss cushions, fallen wood, grass tufts, ant and termite nests) occur. Only , , and are likely to have global populations of similar magnitude, and each of those groups except mites is more inclusive. Though taxonomic rank cannot be used for absolute comparisons, it is notable that nematodes are a phylum and crustaceans a subphylum. Most springtails are small and difficult to see by casual observation, but some springtails, like snow fleas, are readily observed on warm winter days when it is active and its dark color contrasts sharply with a background of snow.
In addition, a few species routinely climb trees and form a dominant component of canopy fauna, where they may be collected by beating or insecticide fogging. In temperate regions, a few species (e.g. Anurophorus laricis, Entomobrya albocincta, Xenylla xavieri, Hypogastrura arborea) are almost exclusively arboreal. In tropical regions a single square meter of canopy habitat can support many species of Collembola.
The main ecological factor driving the local distribution of species is the vertical stratification of the ecosystem: in woodland a continuous change in species assemblages can be observed from tree canopies to ground vegetation then to plant litter down to deeper . This is a complex factor embracing both nutritional and physiological requirements, together with behavioural trends, dispersal limitation and probable species interactions. Some species have been shown to exhibit negative or positive gravitropism, which adds a behavioural dimension to this still poorly understood vertical segregation. Experiments with peat samples turned upside down showed two types of responses to disturbance of this vertical gradient, called stayers and movers.
As a group, springtails are highly sensitive to desiccation, because of their tegumentary respiration, although some species with thin, permeable have been shown to resist severe drought by regulating the osmotic pressure of their body fluid. The gregarious behaviour of Collembola, mostly driven by the attractive power of pheromones excreted by adults, gives more chance to every juvenile or adult individual to find suitable, better protected places, where desiccation could be avoided and reproduction and survival rate rates (thereby fitness) could be kept at an optimum. Sensitivity to drought varies from species to species and increases during ecdysis. Given that springtails moulting repeatedly during their entire life (an ancestral character in Hexapoda) they spend much time in concealed micro-sites where they can find protection against desiccation and predation during ecdysis, an advantage reinforced by Synchronization moulting. The high humidity of many Cave also favours springtails and there are numerous cave adapted species, including one, Plutomurus ortobalaganensis living down the Krubera Cave.
The horizontal distribution of springtail species is affected by environmental factors which act at the landscape scale, such as soil acidity, moisture and light. Requirements for pH can be reconstructed experimentally. Altitudinal changes in species distribution can be at least partly explained by increased acidity at higher elevation. Moisture requirements, among other ecological and behavioural factors, explain why some species cannot live aboveground, or retreat in the soil during dry seasons, but also why some epigeal springtails are always found in the vicinity of Pond and Lake, such as the hygrophilous Isotomurus palustris. Adaptation features, such as the presence of a fan-like wettable mucro, allow some species to move at the surface of water in Fresh water and Marine life environments. Podura aquatica, a unique representative of the family Poduridae (and one of the first springtails to have been described by Carl Linnaeus), spends its entire life at the surface of water, its wettable eggs dropping in water until the non-wettable first instar hatches then surfaces. A few genera are capable of being submerged, and after molting young springtails lose their water repellent properties and are able to survive submerged under water.
In a variegated landscape, made of a patchwork of closed (woodland) and open (, ) environments, most soil-dwelling species are not specialized and can be found everywhere, but most epigeal and litter-dwelling species are attracted to a particular environment, either forested or not. As a consequence of dispersal limitation, landuse change, when too rapid, may cause the local disappearance of slow-moving, specialist species, a phenomenon the measure of which has been called colonisation credit.
Springtails sometimes find their way inside human . However, most Pesticide are not effective against them and moisture-removal strategies are the best line of defense to combat Infestation.
Various sources and publications have suggested that some springtails may parasite humans, but this is entirely inconsistent with their biology, and no such phenomenon has ever been scientifically confirmed, though it has been documented that the scales or hairs from springtails can cause irritation when rubbed onto the skin. They may sometimes be abundant indoors in damp places such as Bathroom and Basement, and incidentally found on one's person. More often, claims of persistent human skin infection by springtails may indicate a neurological problem, such as delusional parasitosis, a psychological rather than entomological problem. Researchers themselves may be subject to psychological phenomena. For example, a publication in 2004 claiming that springtails had been found in skin samples was later determined to be a case of pareidolia; that is, no springtail specimens were actually recovered, but the researchers had digitally enhanced photos of sample debris to create images resembling small arthropod heads, which then were claimed to be springtail remnants. However, Steve Hopkin reports one instance of an entomologist Pooter an Isotoma species and in the process accidentally inhaling some of their eggs, which hatched in his nasal cavity and made him quite ill until they were flushed out.
In 1952, China accused the United States military of spreading bacteria-laden insects and other objects during the Korean War by dropping them from P-51 fighters above rebel villages over North Korea. In all, the U.S. was accused of dropping Ant, , crickets, Flea, Fly, Grasshopper, Louse, , and stoneflies as part of a biological warfare effort. The alleged associated diseases included anthrax, cholera, dysentery, fowl septicemia, paratyphoid, plague, scrub typhus, small pox, and typhoid. China created an international scientific commission for investigating possible bacterial warfare, eventually ruling that the United States probably did engage in limited biological warfare in Korea. The US government denied all the allegations, and instead proposed that the United Nations send a formal inquiry committee to China and Korea, but China and Korea refused to cooperate. U.S. and Canadian entomologists further claimed that the accusations were ridiculous and argued that anomalous appearances of insects could be explained through natural phenomena. Springtail species cited in allegations of biological warfare in the Korean War were Isotoma (Desoria) negishina (a local species) and the "white rat springtail" Folsomia candida.
Captive springtails are often kept in a terrarium as part of a clean-up crew.
Collembola have been found to be useful as Bioindicator of soil quality. Laboratory studies have been conducted that validated that the jumping ability of springtails can be used to evaluate the soil quality of Cu- and Ni-polluted sites.
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