Milnesium alpigenum | |
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Microscope image of the closely related species, M. tardigradum | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Tardigrada |
Class: | Eutardigrada |
Order: | Apochela |
Family: | Milnesiidae |
Genus: | Milnesium |
Species: | M. alpigenum |
Binomial name | |
Milnesium alpigenum Ehrenberg, 1853 | |
Milnesium alpigenum is a species of tardigrade that falls under the Tardigrada phylum. Like its taxonomic relatives it is an omnivorous predator that feeds on other small organisms, such as algae, rotifers, and nematodes. [1] M. alpigenum was discovered by Christian Gottfried Ehrenberg in 1853. [2] It is very closely related to Milnesium tardigradum along with many other species from the Milnesium genus.
M. alpigenum was first suggested to be an independent species by Christian Gottfried Ehrenberg in 1853. [2] However immediately it was turned down to be a valid species due to its extreme morphological similarity to Milnesium tardigradum (Doyère, 1840). This was also because Intraspecific phenotypic variation was thought to be very large between species of tardigrade, and that each species was vastly physiologically different from one another. However, in the early 20th century more research was conducted in relation to the morphological differences within the Milnesium and other tardigrade genuses. It was discovered that any differences between species was very subtle and that all tardigrade were particularly sensitive to reproductive isolating mechanisms. [2]
For almost a century (1853 - 1928) M. alpigenum remained Invalid. [2] In 1928 zoologist Ernst Marcus conducted an experiment, synonymizing M. alpigenum along with Milnesium quadrifidum against M. tardigradum. Marcus concluded small morphological differences in claw configuration between the three species, along with statistical morphometry and DNA sequencing differences. [2] These discoveries cemented M. alpigenum as a valid species and its taxonomic status was confirmed. Due to the sympatric nature of the speciation within most of the Milnesium Genus, the pre-zygotic isolating factors between M. alpigenum and M. tardigradum are currently unknown. Thus it is predicted that these species do breed, but are unable to produce viable offspring due to post-zygotic factors. [1]
Phylogenetically M. alpigenum branches away from the group of sub species M. inceptum (a close relative). Following that it also branches off its closest relative Milnesium tardigradum. Far prior to this it branches of from the other Families of Tardigrade like Diploechiniscus or Echiniscus.
M. alpigenum has a symmetrical roughly rounded body shape with eight legs. Its method of locomotion is to use its six front legs to propel itself through water and to occasionally use its claws to grip onto substrates. Its hind legs often act as a means to push itself off substrates. However, often the tardigrade will simply drift. Individuals have very varied sizes, but some have been measured up to 0.7mm in length. [1]
Tardigrades possess extreme resilience to all sorts of negative Environmental factors such as: extreme radiation levels, extreme temperatures (both high and low), extreme pressures (both high and low), extreme levels of toxins, and extended periods without food or water (up to 10 years). [3] They manage to counteract these extreme environmental stresses by going into a dormant state called cryptobiosis where there metabolism decreases to approximately 0.01% of its regular levels. [4]
There are a very limited amount of unique possible morphological traits within the Milnesium genus with all other traits being common with the greater phylum (See Tardigrade Morphology). The Milnesium specific traits that M. alpigenum possess are as follows: a (3-3)(3-3) claw configuration, the absence of any claw configuration changes as the individual moves to adulthood, a (4+2) peribuccal lamellae body shape, the absence of dorsal cuticle sculpturing, the absence of pseudoplates, a parthenogenesis reproductive mode and (Although not directly morphological) a Palaearctic zoogeographic origin. [5] All of these traits including zoogeographic origin are shared by Milnesium tardigradum except M. Tardigradum has a (2-3)(3-2) claw configuration and the claw configuration changes as M. tardigradum moves to adulthood. [5]
Milnesium alpigenum are found in the Palaearctic realm (Upper Eurasia). They are found in the same ecological area as Milnesium tardigradum and most other Tardigrada species which is aquatic environments such as marine, coastal and terrestrial areas. [4] In fact, tardigrades are so resilient, populous and varied that an individual will likely consume tens of different species of tardigrade possibly including M. alpigenum in a bottle of spring water. [6]
Similarly to almost all Tardigrades, Milnesium alpigenum reproduces both sexually and asexually via parthenogenesis, they do this for reasons similar to those of other asexual organisms like Aphids or Sea Stars. They reproduce asexually to take advantage of resource lucrative environments, as well as to take advantage of limited courting opportunities. Whereas they also (like many organisms that asexually reproduce) reproduce sexually in addition. This allows for M. alpigenum to conquer unreliable/unfamiliar environments by increasing genetic diversity giving higher chances for advantageous traits and thus inter-generational survival. [7]
During sexual reproduction the female lays at most 12 eggs as it sheds it skin, the eggs are then left in the cuticle. Following this, the eggs are then fertilized externally in the cuticle. These take around five to sixteen days to hatch. The hatched larvae undergo various moulting stages that allow them to incrementally reach adulthood. The length of these moulting stages is dependent on the individual's nutrition levels. Finally, once the larvae finish these stages it conducts its final growth moulting phase called ecdysis. After this, the individual has reached reproductive maturity. All tardigrades including M. alpigenum implement the "R" reproductive strategy of having many offspring with little to no investment in growth. The reproductive cycle and nature of M. alpigenum is almost identical to the likes of Milnesium tardigradum. [1]
Where M. alpigenum taxonomically stands was a complex problem that took decades to discover. However where Tardigrades in general stand on the wider tree of life is in itself a mystery. Due to the limited amount of fossil evidence tied to historic specimens of Tardigrades, it is difficult to determine exactly where Tardigrades evolutionarily branch off. Tardigrades have been phylogenetically linked to arthropods and likely has a similar evolutionary history. However, the extent of the relationship is still debated. [4] Other research has shown a shortage in a subset of genes also found in nematodes, another member of the Ecdysozoa superphylum. [8]
Lobopodians are members of the informal group Lobopodia, or the formally erected phylum Lobopoda Cavalier-Smith (1998). They are panarthropods with stubby legs called lobopods, a term which may also be used as a common name of this group as well. While the definition of lobopodians may differ between literatures, it usually refers to a group of soft-bodied, marine worm-like fossil panarthropods such as Aysheaia and Hallucigenia.
In botany, apomixis is asexual development of seed or embryo without fertilization. However, other definitions include replacement of the seed by a plantlet or replacement of the flower by bulbils.
Panarthropoda is a proposed animal clade containing the extant phyla Arthropoda, Tardigrada and Onychophora. Panarthropods also include extinct marine legged worms known as lobopodians ("Lobopodia"), a paraphyletic group where the last common ancestor and basal members (stem-group) of each extant panarthropod phylum are thought to have risen. However the term "Lobopodia" is sometimes expanded to include tardigrades and onychophorans as well.
Tardigrades, known colloquially as water bears or moss piglets, are a phylum of eight-legged segmented micro-animals. They were first described by the German zoologist Johann August Ephraim Goeze in 1773, who called them Kleiner Wasserbär. In 1777, the Italian biologist Lazzaro Spallanzani named them Tardigrada, which means "slow steppers".
Hypsibius dujardini sensu lato is a species complex of tardigrade in the class Eutardigrada. A member of this complex, Hypsibius exemplaris, is widely used for various research projects pertaining to evolutionary biology and astrobiology.
Echiniscus testudo is a cosmopolitan species of tardigrade.
Acutuncus is a genus of tardigrades containing a single species, Acutuncus antarcticus. Tardigrades, which are eight-legged micro-animals, are commonly referred to as water bears or moss piglets and are found all over the world in varying extreme habitats. First discovered in 1904 and originally named Hypsibius antarcticus, Acutuncus antarcticus is the most abundant tardigrade species in Antarctica.
Milnesium tardigradum is a cosmopolitan species of tardigrade that can be found in a diverse range of environments. It has also been found in the sea around Antarctica. M. tardigradum was described by Louis Michel François Doyère in 1840. It contains unidentified osmolytes that could potentially provide important information in the process of cryptobiosis.
Milnesium is a genus of tardigrades. It is rather common, being found in a wide variety of habitats across the world. It has a fossil record extending back to the Cretaceous, the oldest species found so far is known from Turonian stage deposits on the east coast of the United States. Milnesiums are one of the most desiccation and radiation-resistant invertebrates on Earth because of their unique ability to transform into a "tun" state and utilize intrinsically disordered proteins when experiencing extreme environments.
Richtersius is a monospecific genus of tardigrades in the family Richtersiidae; its sole species is Richtersius coronifer. R. coronifer is one of two species of tardigrade that have been shown to survive and continue reproducing after exposure to outer space, specifically in the thermosphere at 258–281 km above sea level with ionizing solar and galactic cosmic radiation for 10 days. However, unlike Milnesium tardigradum, R. coronifer did not survive under these conditions plus UV exposure.
Parthenogenesis is a mode of asexual reproduction in which offspring are produced by females without the genetic contribution of a male. Among all the sexual vertebrates, the only examples of true parthenogenesis, in which all-female populations reproduce without the involvement of males, are found in squamate reptiles. There are about 50 species of lizard and 1 species of snake that reproduce solely through parthenogenesis. It is unknown how many sexually reproducing species are also capable of parthenogenesis in the absence of males, but recent research has revealed that this ability is widespread among squamates.
Milnesium antarcticum is a species of Eutardigrades in the family Milnesiidae. This species differs from its cogenerate species mainly by proportions of its claws and buccopharyngeal apparatus.
Milnesium asiaticum is a species of Eutardigrades in the family Milnesiidae. This species differs from its cogenerate species mainly by proportions of its claws and buccopharyngeal apparatus.
Macrobiotidae is a family of tardigrade. As of 2023, it consists of the following genera:
Macrobiotus is a genus of tardigrade consisting of about 100 species.
Macrobiotus shonaicus is a species of tardigrade in the family Macrobiotidae. As of 2018 it is only known from its type locality: Tsuruoka, Japan. The species description was published in 2018. The insides of their first three pairs of legs have a slight fold above their claws, and their eggs have processes whose terminal discs split off into thin filaments.
Bertolanius is a genus of tardigrades belonging to the family Eohypsibiidae.
Echiniscus madonnae is a tardigrade species, genus of Echiniscus. It was described by Polish zoologists Michalczyk and Kaczmarek Łukasz in South America in 2006, and named in honor of American singer-songwriter Madonna.
Milnesium lagniappe is a species of Eutardigrade in the family Milnesiidae. It is found in the southeastern United States, where it grows on lichens and plant litter. This microscopic creature belongs to the Milnesium granulatum species complex and is characterised by its claw formula, distinct cuticle features and stout claws with well-developed accessory points.
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