Desmacellidae

Desmacellidae is a family of marine demosponges. It is the only family in the monotypic order Desmacellida.
Genera.
The following genera are recognized in the family Desmacellidae:


Martin Heidenhain

Martin Heidenhain (7 December 1864 – 14 December 1949) was a German anatomist born in Breslau. His father was physiologist Rudolf Heidenhain (1834-1937), and his mother, Fanny Volkmann, was the daughter of anatomist Alfred Wilhelm Volkmann (1800-1877).
Martin Heidenhain studied medicine in Freiburg im Breisgau, and in 1890 became an assistant to Albert von Kölliker (1817-1905) at the University of Würzburg. In 1899 he relocated to the University of Tübingen as an associate professor, where he remained for the rest of his career. At Würzburg and Tübingen, he also served as a prosector.
Heidenhain is remembered for his work in comparative anatomy, embryology and histology. He created a few histological stains that bear his name, including an iron haematoxylin stain that is still widely used today. In 1894 he introduced the word "telophase" for the last stage of mitosis.
His principal written work was "Plasma und Zelle" (1907-1911).


Kakapo

The kākāpō ( ,from ), also called owl parrot ("Strigops habroptilus"), is a species of large, flightless, nocturnal, ground-dwelling parrot of the super-family Strigopoidea, endemic to New Zealand.
It has finely blotched yellow-green plumage, a distinct facial disc, a large grey beak, short legs, large feet, and relatively short wings and tail. A combination of traits make it unique among parrots: it is the world's only flightless parrot, the world's heaviest parrot, nocturnal, herbivorous, visibly sexually dimorphic in body size, has a low basal metabolic rate, and no male parental care, and is the only parrot to have a polygynous lek breeding system. It is also possibly one of the world's longest-living birds, with a reported lifespan of up to 100 years.
Its anatomy typifies the tendency of bird evolution on oceanic islands, with few predators and abundant food: a generally robust physique at the expense of flight abilities, resulting in reduced wing muscles and a diminished keel on the sternum. Like many other New Zealand bird species, the kakapo was historically important to Māori, the indigenous people of New Zealand, appearing in many of their traditional legends and folklore; however it was also heavily hunted and used as a resource by Māori, both for its meat as a food source and for its feathers, which were used to make highly valued pieces of clothing. Kakapo were also occasionally kept as pets.
The kakapo is critically endangered; the total known adult population is living individuals, all of which are named and tagged, confined to four small islands off the coast of New Zealand that have been cleared of predators. The introduction of predators such as cats, rats, ferrets, and stoats during British colonisation almost wiped out the kakapo. Conservation efforts began in the 1890s, but they were not very successful until the implementation of the Kakapo Recovery Programme in 1995.
Most kakapo are kept on two predator-free islands, Codfish / Whenua Hou and Anchor, where they are closely monitored, and Little Barrier / Hauturu Island is being trialled as a third home for the species.
Taxonomy, systematics and naming.
The name is Māori, from "kākā" ("parrot") + "pō" ("night"), with little variation across iwi dialects; the term is both singular and plural. "Kākāpō" is increasingly written in New Zealand English with the macrons that indicate long vowels. The name is commonly mispronounced by non-Māori with short As, as “Kah-kah-poe”; efforts to correct this are common in New Zealand during the current revitalisation of the Māori language, and the old pronunciation is becoming far less common.
The kakapo was originally described by English ornithologist George Robert Gray in June 1845 and named "Strigops habroptilus". Its generic name "Strigops" is derived from the Ancient Greek , genitive "owl", and "face", while its specific epithet "habroptilus" comes from "soft", and "feather".
The bird has so many unusual features that it was initially placed in its own tribe, Strigopini. Recent phylogenetic studies have confirmed the unique position of this genus as well as the closeness to the kākā and the kea, both belonging to the New Zealand parrot genus "Nestor". Together, they are now considered a separate superfamily within the parrots, Strigopoidea, the most basal of all living parrots.
Within the Strigopoidea, the kakapo is placed in its own family, Strigopidae. The common ancestor of the kakapo and the genus "Nestor" became isolated from the remaining parrot species when New Zealand broke off from Gondwana, around 82 million years ago. Around 30 million years ago, the kakapo diverged from the genus "Nestor".
Earlier ornithologists felt that the kakapo might be related to the ground parrots and night parrot of Australia due to their similar colouration, but this is contradicted by recent studies; rather, the cryptic colour seems to be adaptation to terrestrial habits that evolved twice convergently.
Description.
The kakapo is a large, rotund parrot. Adults can measure from in length, and weight can vary from at maturity. Males are larger than females. Twenty-eight males were found to average in one study, and 39 males were found to average in another. In the same studies, 28 females were found to average and 18 females were found to average , respectively. Kakapo are the heaviest living species of parrot and on average weigh about more than the largest flying parrot, the hyacinth macaw.
The kakapo cannot fly, having relatively short wings for its size and lacking the keel on the sternum (breastbone), where the flight muscles of other birds attach. It uses its wings for balance and to break its fall when leaping from trees. Unlike many other land birds, the kakapo can accumulate large amounts of body fat.
The upper parts of the kakapo have yellowish moss-green feathers barred or mottled with black or dark brownish grey, blending well with native vegetation. Individuals may have strongly varying degrees of mottling and colour tone and intensity – museum specimens show that some birds had completely yellow colouring. The breast and flank are yellowish-green streaked with yellow. The belly, undertail, neck, and face are predominantly yellowish streaked with pale green and weakly mottled with brownish-grey. Because the feathers do not need the strength and stiffness required for flight, they are exceptionally soft, giving rise to the specific epithet "habroptilus". The kakapo has a conspicuous facial disc of fine feathers resembling the face of an owl; thus, early European settlers called it the "owl parrot". The beak is surrounded by delicate feathers which resemble vibrissae or "whiskers"; it is possible kakapo use these to sense the ground as they walk with its head lowered, but there is no evidence for this. The mandible is variable in colour, mostly ivory, with the upper part often bluish-grey. The eyes are dark brown. Kakapo feet are large, scaly, and, as in all parrots, zygodactyl (two toes face forward and two backward). The pronounced claws are particularly useful for climbing. The ends of the tail feathers often become worn from being continually dragged on the ground.
Females are easily distinguished from males as they have a narrower and less domed head, narrower and proportionally longer beak, smaller cere and nostrils, more slender and pinkish grey legs and feet, and proportionally longer tail. While their plumage colour is not very different from that of the male, the toning is more subtle, with less yellow and mottling. Nesting females also have a brood patch of bare skin on the belly.
The kakapo's altricial young are first covered with greyish white down, through which their pink skin can be easily seen. They become fully feathered at approximately 70 days old. Juvenile individuals tend to have duller green colouration, more uniform black barring, and less yellow present in their feathers. They are additionally distinguishable because of their shorter tails, wings, and beaks. At this stage, they have a ring of short feathers surrounding their irises that resembles eyelashes.
Like many other parrots, kakapo have a variety of calls. As well as the "booms" (see below for a recording) and "chings" of their mating calls, they will often loudly "skraark".
The kakapo has a well-developed sense of smell, which complements its nocturnal lifestyle. It can distinguish between odours while foraging, a behaviour reported in only one other parrot species. The kakapo has a large olfactory bulb ratio (longest diameter of the olfactory bulb/longest diameter of the brain) indicating that it does, indeed, have a more developed sense of smell than other parrots. One of the most striking characteristics of the kakapo is its distinct musty-sweet odour. The smell often alerts predators to the presence of kakapo.
As a nocturnal species, the kakapo has adapted its senses to living in darkness. Its optic tectum, nucleus rotundus, and entopallium are smaller in relation to its overall brain size than those of diurnal parrots. Its retina shares some qualities with that of other nocturnal birds but also has some qualities typical of diurnal birds, lending to best function around twilight. These modifications allow the kakapo to have enhanced light sensitivity but with poor visual acuity.
Internal anatomy.
The skeleton of the kakapo differs from other parrots in several features associated with flightlessness. Firstly, it has the smallest relative wing size of any parrot. Its wing feathers are shorter, more rounded, less asymmetrical, and have fewer distal barbules to lock the feathers together. The sternum is small and has a low, vestigial keel and a shortened spina externa. As in other flightless birds and some flighted parrots, the furcula is not fused but consists of a pair of clavicles lying in contact with each coracoid. As in other flightless birds, the angle between the coracoid and sternum is enlarged. The kakapo has a larger pelvis than other parrots. The proximal bones of the leg and wing are disproportionately long and the distal elements are disproportionately short.
The pectoral musculature of the kakapo is also modified by flightlessness. The pectoralis and supracoracoideus muscles are greatly reduced. The propatagialis tendo longus has no distinct muscle belly. The sternocoracoideus is tendinous. There is an extensive cucularis capitis clavicularis muscle that is associated with the large crop.
Genetics.
Because kakapo passed through a genetic bottleneck, in which their world population was reduced to 49 birds, they are extremely inbred and have low genetic diversity. This manifests in lower disease resistance and fertility problems: 40% of kakapo eggs are infertile. Beginning in 2015, the Kākāpō 125 project aimed to sequence the genome of all living kakapo, as well as some museum specimens – the first time an entire species has had its genome sequenced. The project is a collaboration between Duke University and the New Zealand Genomics lab in Dunedin.
Habitat.
Before the arrival of humans, the kakapo was distributed throughout both main islands of New Zealand. Although it may have inhabited Stewart Island before human arrival, it has so far not been found in the extensive fossil collections from there. Kakapo lived in a variety of habitats, including tussocklands, scrublands and coastal areas. It also inhabited forests dominated by podocarps (rimu, matai, kahikatea, totara), beeches, tawa, and rata. In Fiordland, areas of avalanche and slip debris with regenerating and heavily fruiting vegetation – such as five finger, wineberry, bush lawyer, tutu, hebes, and coprosmas – became known as "kakapo gardens".
The kakapo is considered to be a "habitat generalist". Though they are now confined to islands free of predation, they were once able to live in nearly any climate present on the islands of New Zealand. They survived dry, hot summers on the North Island as well as cold winter temperatures in the sub-alpine areas of Fiordland. Kakapo seem to have preferred broadleaf or mountain beech and Hall's tōtara forest with mild winters and high rainfall, but the species was not exclusively forest-dwelling. All kakapo that were transferred to predator-free islands in the last decades have adapted well to any changes in environment and food plants.
Ecology and behaviour.
It seems that the kakapo – like many of New Zealand's bird species – has evolved to occupy an ecological niche normally filled by various species of mammal (the only non-marine mammals native to New Zealand are ).
The kakapo is primarily nocturnal; it roosts under cover in trees or on the ground during the day and moves around its territories at night.
Though the kakapo cannot fly, it is an excellent climber, ascending to the crowns of the tallest trees. It can also "parachute" – descending by leaping and spreading its wings. In this way it may travel a few metres at an angle of less than 45 degrees. With only 3.3% of its mass made up of pectoral muscle, it is no surprise that the kakapo cannot use its wings to lift its heavy body off the ground. Because of its flightlessness, it has very low metabolic demands in comparison to flighted birds. It is able to survive easily on very little or on very low quality food sources. Unlike most other bird species, the kakapo is entirely herbivorous, feeding on fruits, seeds, leaves, stems, and rhizomes. When foraging, kakapo tend to leave crescent-shaped wads of fiber in the vegetation behind them, called "browse signs".
Having lost the ability to fly, it has developed strong legs. Locomotion is often by way of a rapid "jog-like" gait by which it can move several kilometres. A female has been observed making two return trips each night during nesting from her nest to a food source up to away and the male may walk from its home range to a mating arena up to away during the mating season (October–January).
Young birds indulge in play fighting, and one bird will often lock the neck of another under its chin. The kakapo is curious by nature and has been known to interact with humans. Conservation staff and volunteers have engaged extensively with some kakapo, which have distinct personalities. While they are curious toward humans, kakapo are not social birds.
The kakapo was a very successful species in pre-human New Zealand, and was well adapted to avoid the birds of prey which were their only predators. As well as the New Zealand falcon, there were two other birds of prey in pre-human New Zealand: Haast's eagle and Eyles' harrier. All these raptors soared overhead searching for prey in daylight, and to avoid them the kakapo evolved camouflaged plumage and became nocturnal. When a kakapo feels threatened, it freezes, so that it is more effectively camouflaged in the vegetation its plumage resembles. Kakapo were not entirely safe at night, when the laughing owl was active, and it is apparent from owl nest deposits on Canterbury limestone cliffs that kakapo were among their prey.
Kakapo defensive adaptations were no use, however, against the mammalian predators introduced to New Zealand by humans. Birds hunt very differently from mammals, relying on their powerful vision to find prey, and thus they usually hunt by day. Mammalian predators, in contrast to birds, often hunt by night, and rely on their sense of smell and hearing to find prey; a common way for humans to hunt kakapo was by releasing trained dogs. The kakapo's adaptations to avoid avian predation have thus been useless against its new enemies, and the reason for its massive decline since the introduction of dogs, cats and mustelids (see "Conservation: Human impact").
Breeding.
The kakapo is the only extant species of flightless parrot in the world, and the only flightless bird that has a lek breeding system. Males loosely gather in an arena and compete with each other to attract females. Females listen to the males as they display, or "lek". They choose a mate based on the quality of his display; they are not pursued by the males in any overt way. No pair bond is formed; males and females meet only to mate.
During the courting season, males leave their home ranges for hilltops and ridges where they establish their own mating courts. These leks can be up to from a kakapo's usual territory and are an average of apart within the lek arena. Males remain in the region of their court throughout the courting season. At the start of the breeding season, males will fight to try to secure the best courts. They confront each other with raised feathers, spread wings, open beaks, raised claws and loud screeching and growling. Fighting may leave birds with injuries or even kill them. Mating occurs only approximately every five years, with the ripening of the rimu fruit. In mating years, males making "booming" calls for 6–8 hours every night for more than four months.
Each court consists of one or more saucer-shaped depressions or "bowls" dug in the ground by the male, up to deep and long enough to fit the half-metre length of the bird. The kakapo is one of only a handful of birds in the world which actually constructs its leks. Bowls are often created next to rock faces, banks, or tree trunks to help reflect sound: the bowls themselves function as amplifiers to enhance the projection of the males' booming mating calls. Each male's bowls are connected by a network of trails or tracks which may extend along a ridge or in diameter around a hilltop. Males meticulously clear their bowls and tracks of debris. One way researchers check whether bowls are visited at night is to place a few twigs in the bowl; if the male visits overnight, he will pick them up in his beak and toss them away.
To attract females, males make loud, low-frequency (below 100 Hz) booming calls from their bowls by inflating a thoracic sac. They start with low grunts, which increase in volume as the sac inflates. After a sequence of about 20 loud booms, the male kakapo emits a high-frequency, metallic "ching" sound. He stands for a short while before again lowering his head, inflating his chest and starting another sequence of booms. The booms can be heard at least away on a still night; wind can carry the sound at least . Males boom for an average of eight hours a night; each male may produce thousands of booms in this time. This may continue every night for three or four months during which time the male may lose half his body weight. Each male moves around the bowls in his court so that the booms are sent out in different directions. These booms are also notorious for attracting predators, because of the long range at which they can be heard.
Females are attracted by the booms of the competing males; they too may need to walk several kilometres from their territories to the arena. Once a female enters the court of one of the males, the male performs a display in which he rocks from side to side and makes clicking noises with his beak. He turns his back to the female, spreads his wings in display and walks backwards towards her. He will then attempt copulation for 40 minutes or more. Once the birds have mated, the female returns to her home territory to lay eggs and raise the chicks. The male continues booming in the hope of attracting another female.
The female kakapo lays 1–4 eggs per breeding cycle, with several days between eggs. She nests on the ground under the cover of plants or in cavities such as hollow tree trunks. The female incubates the eggs faithfully, but is forced to leave them every night in search of food. Predators are known to eat the eggs, and the embryos inside can also die of cold in the mother's absence. Kakapo eggs usually hatch within 30 days, bearing fluffy grey chicks that are quite helpless. After the eggs hatch, the female feeds the chicks for three months, and the chicks remain with the female for some months after fledging. The young chicks are just as vulnerable to predators as the eggs, and young have been killed by many of the same predators that attack adults. Chicks leave the nest at approximately 10 to 12 weeks of age. As they gain greater independence, their mothers may feed the chicks sporadically for up to 6 months.
Because the kakapo is long-lived, with an average life expectancy of 60 (plus or minus 20) years, it tends to have an adolescence before it starts breeding. Males start booming at about 5 years of age. It was thought that females reached sexual maturity at 9 years of age, but four five-year-old females have now been recorded reproducing. The kakapo does not breed every year and has one of the lowest rates of reproduction among birds. Breeding occurs only in years when trees mast (fruit heavily), providing a plentiful food supply. Rimu mast occurs only every three to five years, so in rimu-dominant forests, such as those on Whenua Hou, kakapo breeding occurs as infrequently.
Another aspect of the kakapo's breeding system is that a female can alter the sex ratio of her offspring depending on her condition. A female in good condition produces more male offspring (males have 30%–40% more body weight than females). Females produce offspring biased towards the dispersive sex when competition for resources (such as food) is high and towards the non-dispersive sex when food is plentiful. A female kakapo will likely be able to produce eggs even when there are few resources, while a male kakapo will be more capable of perpetuating the species when there are plenty, by mating with several females. This supports the Trivers–Willard hypothesis. The relationship between clutch sex ratio and maternal diet has conservation implications, because a captive population maintained on a high quality diet will produce fewer females and therefore fewer individuals valuable to the recovery of the species.
Feeding.
The beak of the kakapo is adapted for grinding food finely. For this reason, the kakapo has a very small gizzard compared to other birds of their size. It is entirely herbivorous, eating native plants, seeds, fruits, pollen and even the sapwood of trees. A study in 1984 identified 25 plant species as kakapo food. It is particularly fond of the fruit of the rimu tree, and will feed on it exclusively during seasons when it is abundant. The kakapo strips out the nutritious parts of the plant out with its beak, leaving a ball of indigestible fibre. These little clumps of plant fibres are a distinctive sign of the presence of the bird. The kakapo is believed to employ bacteria in the fore-gut to ferment and help digest plant matter.
Kakapo diet changes according to the season. The plants eaten most frequently during the year include some species of "Lycopodium ramulosum", "Lycopodium fastigium", "Schizaea fistulosa", "Blechnum minus", "Blechnum procerum", "Cyathodes juniperina", "Dracophyllum longifolium", "Olearia colensoi" and "Thelymitra venosa". Individual plants of the same species are often treated differently. Kakapo leave conspicuous evidence of their feeding activities, over feeding areas that range between and per individual. Kakapo feeding grounds almost always host manuka and yellow silver pine ("Lepidothamnus intermedius") scrubs.
Conservation.
Fossil records indicate that in pre-Polynesian times, the kakapo was New Zealand's third most common bird and it was widespread on all three main islands. However, the kakapo population in New Zealand has declined massively since human settlement of the country, and its conservation status as ranked by the Department of Conservation continues to be "Nationally Critical". Since the 1890s, conservation efforts have been made to prevent extinction. The most successful scheme has been the Kakapo Recovery Programme; this was implemented in 1995 and continues.
Human impact.
The first factor in the decline of the kakapo was the arrival of humans. Māori folklore suggests that the kakapo was found throughout the country when the Polynesians first arrived in Aotearoa 700 years ago. Subfossil and midden deposits show that the bird was present throughout the North and South Island before and during early Māori times. Māori hunted the kakapo for food and for their skins and feathers, which were made into cloaks.
Due to its inability to fly, strong scent and habit of freezing when threatened, the kakapo was easy prey for the Māori and their dogs. Its eggs and chicks were also preyed upon by the Polynesian rat or kiore, which the Māori brought to New Zealand as a stowaway. Furthermore, the deliberate clearing of vegetation by Māori reduced the habitable range for kakapo. Although the kakapo was extinct in many parts of the islands by the time Europeans arrived, including the Tararua and Aorangi Ranges, it was locally abundant in parts of New Zealand, such as the central North Island and forested parts of the South Island.
Although kakapo numbers were reduced by Māori settlement, they declined much more rapidly after European colonisation. Beginning in the 1840s, Pākehā settlers cleared vast tracts of land for farming and grazing, further reducing kakapo habitat. They brought more dogs and other mammalian predators, including domestic cats, black rats and stoats. Europeans knew little of the kakapo until George Gray of the British Museum described it from a skin in 1845. As the Māori had done, early European explorers and their dogs ate kakapo. In the late 19th century, the kakapo became well known as a scientific curiosity, and thousands were captured or killed for zoos, museums and collectors. Most captured specimens died within months. From at least the 1870s, collectors knew the kakapo population was declining; their prime concern was to collect as many as possible before the bird became extinct.
In the 1880s, large numbers of mustelids (stoats, ferrets and weasels) were released in New Zealand to reduce rabbit numbers, but they also preyed heavily on many native species including the kakapo. Other browsing animals, such as introduced deer, competed with the kakapo for food, and caused the extinction of some of its preferred plant species. The kakapo was reportedly still present near the head of the Whanganui River as late as 1894, with one of the last records of a kakapo in the North Island being a single bird caught in the Kaimanawa Ranges by Te Kepa Puawheawhe in 1895.
Early protection efforts.
In 1891, the New Zealand government set aside Resolution Island in Fiordland as a nature reserve. In 1894, the government appointed Richard Henry as caretaker. A keen naturalist, Henry was aware that native birds were declining, and began catching and moving kakapo and kiwi from the mainland to the predator-free Resolution Island. In six years, he moved more than 200 kakapo to Resolution Island. By 1900, however, stoats had swum to Resolution Island and colonised it; they wiped out the nascent kakapo population within 6 years.
In 1903, three kakapo were moved from Resolution Island to the nature reserve of Little Barrier Island (Hauturu-o-Toi) north-east of Auckland, but feral cats were present and the kakapo were never seen again. In 1912, three kakapo were moved to another reserve, Kapiti Island, north-west of Wellington. One of them survived until at least 1936, despite the presence of feral cats for part of the intervening period.
By the 1920s, the kakapo was extinct in the North Island and its range and numbers in the South Island were declining. One of its last refuges was rugged Fiordland. There, during the 1930s, it was often seen or heard, and occasionally eaten, by hunters or roadworkers. By the 1940s, reports of kakapo were becoming scarce.
1950–1989 conservation efforts.
In the 1950s, the New Zealand Wildlife Service was established and began making regular expeditions to search for the kakapo, mostly in Fiordland and what is now the Kahurangi National Park in the northwest of the South Island. Seven Fiordland expeditions between 1951 and 1956 found only a few recent signs. Finally, in 1958 a kakapo was caught and released in the Milford Sound catchment area in Fiordland. Six more kakapo were captured in 1961; one was released and the other five were transferred to the aviaries of the Mount Bruce Bird Reserve near Masterton in the North Island. Within months, four of the birds had died and the fifth died after about four years. In the next 12 years, regular expeditions found few signs of the kakapo, indicating that numbers were continuing to decline. Only one bird was captured in 1967; it died the following year.
By the early 1970s, it was uncertain whether the kakapo was still an extant species. At the end of 1974, scientists located several more male kakapo and made the first scientific observations of kakapo booming. These observations led Don Merton to speculate for the first time that the kakapo had a lek breeding system. From 1974 to 1978 a total of 18 kakapo were discovered in Fiordland, but all were males. This raised the possibility that the species would become extinct, because there might be no surviving females. One male bird was captured in the Milford area in 1975, christened "Richard Henry", and transferred to Maud Island. All the birds the Wildlife Service discovered from 1951 to 1976 were in U-shaped glaciated valleys flanked by almost-vertical cliffs and surrounded by high mountains. Such extreme terrain had slowed colonisation by browsing mammals, leaving islands of virtually unmodified native vegetation. However, even here, stoats were present and by 1976 the kakapo was gone from the valley floors and only a few males survived high on the most inaccessible parts of the cliffs.
Before 1977, no expedition had been to Stewart Island/Rakiura to search for the bird. In 1977, sightings of kakapo were reported on Stewart Island. An expedition to the island found a track and bowl system on its first day; soon after, it located several dozen kakapo. The finding in an 8,000-hectare area of fire-modified scrubland and forest raised hope that the population would include females. The total population was estimated at 100 to 200 birds.
Mustelids have never colonised Stewart Island/Rakiura, but feral cats were present. During a survey, it was apparent that cats killed kakapo at a rate of 56% per year. At this rate, the birds could not survive on the island and therefore an intensive cat control was introduced in 1982, after which no cat-killed kakapo were found. However, to ensure the survival of the remaining birds, scientists decided later that this population should be transferred to predator-free islands; this operation was carried out between 1982 and 1997.
Kakapo Recovery programme.
In 1989, a Kakapo Recovery plan was developed, and a Kakapo Recovery programme was established in 1995. The New Zealand Department of Conservation replaced the Wildlife Service for this task.
The first action of the plan was to relocate all the remaining kakapo to suitable islands for them to breed. None of the New Zealand islands were ideal to establish kakapo without rehabilitation by extensive re-vegetation and the eradication of introduced mammalian predators and competitors. Four islands were finally chosen: Maud, Hauturu/Little Barrier, Codfish and Mana. Sixty-five kakapo (43 males, 22 females) were successfully transferred onto the four islands in five translocations. Some islands had to be rehabilitated several times when feral cats, stoats and weka kept appearing. Little Barrier Island was eventually viewed as unsuitable due to the rugged landscape, the thick forest and the continued presence of rats, and its birds were evacuated in 1998. Along with Mana Island, it was replaced with two new kakapo sanctuaries: Chalky Island (Te Kakahu) and Anchor Island. The entire kakapo population of Codfish Island was temporarily relocated in 1999 to Pearl Island in Port Pegasus while rats were being eliminated from Codfish. All kakapo on Pearl and Chalky Islands were moved to Anchor Island in 2005.
Supplementary feeding.
A key part of the Recovery Programme is the supplementary feeding of females. Kakapo breed only once every two to five years, when certain plant species, primarily "Dacrydium cupressinum" (rimu), produce protein-rich fruit and seeds. During breeding years when rimu masts supplementary food is provided to kakapo to increase the likelihood of individuals successfully breeding. In 1989, six preferred foods (apples, sweet potatoes, almonds, Brazil nuts, sunflower seeds and walnuts) were supplied "ad libitum" each night to 12 feeding stations. Males and females ate the supplied foods, and females nested on Little Barrier Island in the summers of 1989–1991 for the first time since 1982, although nesting success was low.
Supplementary feeding affects the sex ratio of kakapo offspring, and can be used to increase the number of female chicks by deliberately manipulating maternal condition. During the winter of 1981, only females lighter than were given supplementary feeding to avoid raising their body condition, and the sex ratio results in 1982 were close to parity, eliminating the male-biased sex ratios in the unrestricted feeding.
Today commercial parrot food is supplied to all individuals of breeding age on Whenua Hou and Anchor. The amount eaten and individual weights are carefully monitored to ensure that optimum body condition is maintained.
Nest management.
Kakapo nests are intensively managed. Before Polynesian rats were removed from Whenua Hou, they were a threat to the survival of young kakapo. Of 21 chicks that hatched between 1981 and 1994, nine were either killed by rats or died and were subsequently eaten by rats. Nest protection was intensified after 1995 by using traps and poison stations as soon as a nest was detected. A small video camera and infra-red light source would watch the nest continuously, and scare approaching rats with flashing lights and loud popping sounds.
All kakapo islands are now rat-free, but infrared cameras still allow rangers to remotely monitor the behaviour of females and chicks in nests. Data loggers record when mother kakapo come and go, allowing rangers to pick a time to check on the health of chicks, and also indicate how hard females are having to work to find food. Because mother kakapo often struggle to successfully rear multiple chicks, Kakapo Recovery rangers will move chicks between nests as needed.
Eggs are often removed from nests for incubation to reduce the likelihood of accidents, such as lost eggs or crushing. If chicks become ill, aren’t putting on weight, or there are too many chicks in the nest (and no available nest to move them to) they will be hand-reared by the Kakapo Recovery team. In the 2019 season, eggs were also removed from nests to encourage females to re-nest. By hand-raising the first group of chicks in captivity and encouraging females to lay more eggs, the Kakapo Recovery Team hoped that overall chick production would be increased. By the end of February 2020, the bird's summer breeding season, these efforts led to the production of 80 chicks, "a record number."
Monitoring.
To monitor the kakapo population continuously, each bird is equipped with a radio transmitter. Every known kakapo, barring some young chicks, has been given a name by Kakapo Recovery Programme officials, and detailed data is gathered about every individual. GPS transmitters are also being trialled to provide more detailed data about the movement of individual birds and their habitat use. The signals also provide behavioural data, letting rangers gather information about mating and nesting remotely. Every individual kakapo receives an annual health check and has their transmitter replaced.
Reintroduction.
The Kakapo Recovery programme has been successful, with the numbers of kakapo increasing steadily. Adult survival rate and productivity have both improved significantly since the programme's inception. However, the main goal is to establish at least one viable, self-sustaining, unmanaged population of kakapo as a functional component of the ecosystem in a protected habitat. To help meet this conservation challenge, Resolution Island (20,860 ha) in Fiordland has been prepared for kakapo re-introduction with ecological restoration including the eradication of stoats. Ultimately, the Kakapo Recovery vision for the species is to restore the "mauri" (Maori for "life-force") of the kakapo by breeding 150 adult females.
Fatal fungal infection.
In late April 2019, the first case of the fungal disease "aspergillosis" in New Zealand kākāpō was discovered. almost 20% of the population, or 36 birds, have been flown by helicopter to veterinary hospitals around New Zealand for CT scan diagnosis and intensive treatment that usually lasted for several months.
Dunedin's Wildlife Hospital has treated 12 birds.
In Māori culture.
The kakapo is associated with a rich tradition of Māori folklore and beliefs. The bird's irregular breeding cycle was understood to be associated with heavy fruiting or "masting" events of particular plant species such as the rimu, which led Māori to credit the bird with the ability to tell the future. Used to substantiate this claim were reported observations of these birds dropping the berries of the hinau and tawa trees (when they were in season) into secluded pools of water to preserve them as a food supply for the summer ahead; in legend this became the origin of the Māori practice of immersing food in water for the same purpose.
Use for food and clothing.
The meat of kakapo made good eating and was considered by Māori to be a delicacy and it was hunted for food when it was still widespread. One source states that its flesh "resembles lamb in taste and texture", although European settlers have described the bird as having a "strong and slightly stringent [sic] flavour".
In breeding years, the loud booming calls of the males at their mating arenas made it easy for Māori hunting parties to track the kakapo down, and it was also hunted while feeding or when dust-bathing in dry weather. The bird was caught, generally at night, using snares, pitfall traps, or by groups of domesticated Polynesian dogs which accompanied hunting parties – sometimes they would use fire sticks of various sorts to dazzle a bird in the darkness, stopping it in their tracks and making the capture easier. Cooking was done in a hāngi or in gourds of boiling oil. The flesh of the bird could be preserved in its own fat and stored in containers for later consumption – hunters of the Ngāi Tahu tribe would pack the flesh in baskets made from the inner bark of totara tree or in containers constructed from kelp. Bundles of kakapo tail feathers were attached to the sides of these containers to provide decoration and a way to identify their contents. Also taken by the Māori were the bird's eggs, which are described as whitish "but not pure white", and about the same size as a kererū egg.
As well as eating the meat of the kakapo, Māori would use kakapo skins with the feathers still attached or individually weave in kakapo feathers with flax fibre to create cloaks and capes. Each one required up to 11,000 feathers to make. Not only were these garments considered very beautiful, they also kept the wearer very warm. They were highly valued, and the few still in existence today are considered "taonga" (treasures) – indeed, the old Māori adage "You have a kākāpō cape and you still complain of the cold" was used to describe someone who is never satisfied. Kakapo feathers were also used to decorate the heads of taiaha, but were removed before use in combat.
Despite this, the kakapo was also regarded as an affectionate pet by the Māori. This was corroborated by European settlers in New Zealand in the 19th century, among them George Edward Grey, who once wrote in a letter to an associate that his pet kakapo's behaviour towards him and his friends was "more like that of a dog than a bird".
In the media.
The conservation of the kakapo has made the species well known. Many books and documentaries detailing the plight of the kakapo have been produced in recent years, one of the earliest being "Two in the Bush", made by Gerald Durrell for the BBC in 1962.
A feature-length documentary, "The Unnatural History of the Kakapo" won two major awards at the Reel Earth Environmental Film Festival. Two of the most significant documentaries, both made by NHNZ, are "Kakapo – Night Parrot" (1982) and "To Save the Kakapo" (1997).
The BBC's Natural History Unit also featured the kakapo, including a sequence with Sir David Attenborough in "The Life of Birds". It was also one of the endangered animals Douglas Adams and Mark Carwardine set out to find for the radio series and book "Last Chance to See". An updated version of the series has been produced for BBC TV, in which Stephen Fry and Carwardine revisit the animals to see how they are getting on almost 20 years later, and in January 2009, they spent time filming the kakapo on Codfish Island. Footage of a kakapo named Sirocco attempting to mate with Carwardine's head was viewed by millions worldwide, leading to Sirocco becoming "spokes-bird" for New Zealand wildlife conservation in 2010. Sirocco became the inspiration for the party parrot, a popular animated emoji frequently associated with the workflow application Slack.
The kakapo was featured in the episode "Strange Islands" of the documentary series "South Pacific", originally aired on 13 June 2009, in the episode "Worlds Apart" of the series "The Living Planet", and in episode 3 of the BBC's "New Zealand Earth's Mythical Islands".
In a 2019 kakapo awareness campaign, the Kakapo Recovery Programme New Zealand National Partner, Meridian Energy, ran a "Search for a Saxophonist" to provide suitable mood music for encouraging mating to coincide with the 2019 kakapo breeding season. The search and footage from the islands where breeding was taking place were featured on the "One News Breakfast" programme.
The bird was named New Zealand's bird of the year in 2008 and 2020.
External links.
[[Category:Birds described in 1845]]
[[Category:Endemic birds of New Zealand]]
[[Category:Flightless birds]]
[[Category:Māori culture]]
[[Category:Parrots of Oceania]]
[[Category:Strigopidae]]
[[Category:Taxa named by George Robert Gray]]


Anterior superior alveolar arteries

The anterior superior alveolar arteries originate from the infraorbital artery; they supply the upper incisors and canines; they also supply the mucous membrane of the maxillary sinus.


Oncopoda

Oncopoda is a hypothetical group of animals comprising the Onychophora, Tardigrada and Pentastomida.


Essonodon

Essonodon is a mammal genus from the Upper Cretaceous of North America. It was a member of the extinct order Multituberculata and lived towards the end of the "age of the dinosaurs." It is within the suborder Cimolodonta and perhaps the family Cimolomyidae.
The genus "Essonodon" was named by Simpson G.G. in 1927, and is also partly known as "Cimolodon". The inclusion of this taxon within Cimolomyidae is tentative. (Kielan-Jaworowska & Hurum 2001, p. 408).
The species: "Essonodon browni" has also partly been known as "Cimolodon nitidus" (Marsh 1889).
Place: Hell Creek, Montana & San Juan Basin, New Mexico & Wyoming (USA)

Age: Maastrichtian (Upper Cretaceous)

This species was a large multituberculate that weighed in at over 2.5 kilograms. Further material has been reported from the Frenchman Formation of Canada.


Hedydipna

 Hedydipna is a genus of sunbirds. It contains the following species, which are sometimes included in genus "Anthreptes".
The name "Hedydipna" comes from the Greek "hēdudeipnos", meaning "dainty-supping" or "sweet-eating" — a reference to the nectar sipping habits of these species. These sunbirds are largely restricted to Africa and western islands in the Indian Ocean, though the Nile Valley sunbird is found as far east as Yemen.


George Philip Farran

George Philip Farran (1876–1949) was an Irish zoologist. He was an expert on Copepoda.
Farran initially worked in the National Museum and in the Royal Dublin Society's Fishery Survey. He was appointed Assistant Naturalist with the Department of Agriculture & Technical Instruction Fisheries Branch in 1901, and became an Inspector in 1909 and in 1938 Chief Inspector.
Personal life and education.
He was born on 21 November 1876 at Templeogue, the son of Edmond Chomley Farran and his wife Anne Hume Ryan; his father, who was independently wealthy, died in 1881. He attended the school at Rathmines run by Charles William Benson, an enthusiast for natural history, and entered the Trinity College, Dublin law school in 1895. Later he graduated in Natural Science winning the Gold Medal of the subject for his class.
Farran's studies of marine wildlife began at the Marine Laboratory in Ballynakill Co. Galway with a small group of scientists gathered by Ernest William Lyons Holt, in 1898. It focused on marine biological issues of the fishery. Farran joined the Department of Agriculture and Technical Instruction in 1900. He became Inspector of Fisheries in 1910, when Holt was promoted.
During World War I, Farran served in the King's (Liverpool) Regiment. He was in Egypt and Palestine, and left the army in 1919. In 1920 he married Georgina Margaret Craig, and they had a son and a daughter.
In 1938 Farran was promoted, becoming the Chief Inspector of Fisheries. He continued his work with the Department until his retirement in 1946.
Studies.
Farran's work was first based on a broad range of marine zoology: it was later in his career that he began his work on planktonic organisms for which he is best known. He specifically studied copepods, which are aquatic crustaceans.
Farran was brought material from around the world by other scientists. He was widely published scientist, with work published journals, including those of the Royal Irish Academy and Linnean Society of London, "Exploration of the Sea", and by the Zoological Society. Most of his work was published in the Scientific Investigations of the Fisheries Branch of the Department of Agriculture and Technical Instruction.
When he began nearing the end of his career his work was more focused on the administrative side of his job rather than the scientific work he preferred. Farran did still manage to continue his work with planktonic organisms throughout the remainder of his life even close to his death on January 5, 1949 at the age of 72. Farran still studied after his retirement, and even participated in an experiment of breeding of oysters in tanks at Cromane, Co Kerry in 1947 and 1948 just before he died.


Aplysina archeri

Aplysina archeri, also known as a stove-pipe sponge because of its shape, is a species of tube sponge that has long tube-like structures of cylindrical shape. Although they can grow in a single tube, they often grow in large groups of up to 22 tubes. A single tube can grow up to high and thick. These sponges mostly live in the Western Atlantic Ocean: the Caribbean, The Bahamas, Florida, and Bonaire. Like most sponges, they are filter feeders; they eat food such as plankton or suspended detritus as it passes them. Very little is known about their behavioral patterns except for their feeding ecology and reproductive biology. Tubes occur in varying colors including lavender, pink, gray, and brown. They reproduce both by asexual and sexual reproduction. These sponges take hundreds of years to grow and never stop growing until they die. Snails are among their natural predators. The population density of these sponges is going down because of oil spills and other pollution.


Calypter

A calypter is either of two posterior lobes of the posterior margin of the forewing of flies between the extreme posterior wing base and the alula, which covers the halteres.
The lower calypter is the proximal calypter (synonyms: squama (of some authors), tegula) and the upper calypter is the distal calypter (synonym: squamula).
Species of the subsection Acalyptratae are noted for lacking calypters.


Mariner transposon


Subclavian triangle

The subclavian triangle (or supraclavicular triangle, omoclavicular triangle, Ho's triangle), the smaller division of the posterior triangle, is bounded, above, by the inferior belly of the omohyoideus; below, by the clavicle; its base is formed by the posterior border of the sternocleidomastoideus.
Its floor is formed by the first rib with the first digitation of the serratus anterior.
The size of the subclavian triangle varies with the extent of attachment of the clavicular portions of the Sternocleidomastoideus and Trapezius, and also with the height at which the Omohyoideus crosses the neck.
Its height also varies according to the position of the arm, being diminished by raising the limb, on account of the ascent of the clavicle, and increased by drawing the arm downward, when that bone is depressed.
This space is covered by the integument, the superficial and deep fasciæ and the platysma, and crossed by the supraclavicular nerves.
Just above the level of the clavicle, the third portion of the subclavian artery curves lateralward and downward from the lateral margin of the scalenus anterior, across the first rib, to the axilla, and this is the situation most commonly chosen for ligaturing the vessel.
Sometimes this vessel rises as high as 4 cm. above the clavicle; occasionally, it passes in front of the Scalenus anterior, or pierces the fibers of that muscle.
The subclavian vein lies behind the clavicle, and is not usually seen in this space; but in some cases it rises as high as the artery, and has even been seen to pass with that vessel behind the Scalenus anterior.
The brachial plexus of nerves lies above the artery, and in close contact with it. Passing transversely behind the clavicle are the transverse scapular vessels; and traversing its upper angle in the same direction, the transverse cervical artery and vein.
The external jugular vein runs vertically downward behind the posterior border of the Sternocleidomastoideus, to terminate in the subclavian vein; it receives the transverse cervical and transverse scapular veins, which form a plexus in front of the artery, and occasionally a small vein which crosses the clavicle from the cephalic.
The small nerve to the subclavius also crosses this triangle about its middle, and some lymph glands are usually found in the space.
Enlarged nodes in this triangle irrespective of size are categorized at N3 in the TNM classification for nasopharyngeal carcinoma.


Metaphysis

The metaphysis is the neck portion of a long bone between the epiphysis and the diaphysis. It contains the growth plate, the part of the bone that grows during childhood, and as it grows it ossifies near the diaphysis and the epiphyses. The metaphysis contains a diverse population of cells including mesenchymal stem cells, which give rise to bone and fat cells, as well as hematopoietic stem cells which give rise to a variety of blood cells as well as bone-destroying cells called osteoclasts. Thus the metaphysis contains a highly metabolic set of tissues including trabecular (spongy) bone, blood vessels , as well as Marrow Adipose Tissue (MAT).
The metaphysis may be divided anatomically into three components based on tissue content: a cartilaginous component (epiphyseal plate), a bony component (metaphysis) and a fibrous component surrounding the periphery of the plate. The growth plate synchronizes chondrogenesis with osteogenesis or interstitial cartilage growth with appositional bone growth at the same that it is growing in width, bearing load and responding to local and systemic forces and factors.
During childhood, the growth plate contains the connecting cartilage enabling the bone to grow; at adulthood (between the ages of 18 to 25 years), the components of the growth plate stop growing altogether and completely ossify into solid bone. In an adult, the metaphysis functions to transfer loads from weight-bearing joint surfaces to the diaphysis.
Clinical significance.
Because of their rich blood supply and vascular stasis, metaphyses of long bones are prone to hematogenous spread of osteomyelitis in children.
Metaphyseal tumors or lesions include osteosarcoma, chondrosarcoma, fibrosarcoma, osteoblastoma, enchondroma, fibrous dysplasia, simple bone cyst, aneurysmal bone cyst, non-ossifying fibroma, and osteoid osteoma.
One of the clinical signs of rickets that doctors look for is cupping and fraying at the metaphyses when seen on X-ray.


Zygosphene-zygantrum articulation

The zygosphene-zygantrum articulation is an accessory joint between vertebrae found in several lepidosauromorph reptiles. This pivot joint consists of a forward-facing, wedge-shaped process called the zygosphene, that fits in a depression on the rearside of the next vertebrae, called the zygantrum. The zygosphene sits between the prezygapophysis in the neural arch, whereas the zygantrum sits between the postzygapophysis.
This joint is found in snakes, lacertids, teiids, Gymnophthalmids as well as in some iguanids and cordylids. It is also found in several fossil groups such as plesiosaurians, nothosaurians and pachypleurosaurians. It is absent in today's Monitor lizard ("Varanus"), but occurs in fossil Varanids.
The zygosphene-zygantrum joint's function is to stabilize the vertebral column. While it permits horizontal and vertical movements of the vertebral column, it prevents rotations of the single vertebrae against each other.


Filospermoidea

Filospermoidea is an order within the phylum Gnathostomulida. Filospermoids are generally longer than gnathostomulids in the order Bursovaginoidea, and have an elongate rostrum. It lives in North America, off the coasts of the southern United States and the Caribbean, primarily in the Gulf of Mexico, as well as in southeastern Denmark.
Classification.
The order Filospermoidea contains 29 species in 2 families and 3 genera.


Neuronal self-avoidance

Neuronal self-avoidance, or isoneural avoidance, is an important property of neurons which consists in the tendency of branches (dendrites and axons) arising from a single soma (also called isoneuronal or sister branches) to turn away from one another. The arrangements of branches within neuronal arbors are established during development and result in minimal crossing or overlap as they spread over a territory, resulting in the typical fasciculated morphology of neurons (Fig 1).
In opposition, branches from different neurons can overlap freely with one another. This propriety demands that neurons are able to discriminate "self", which they avoid, from "non-self" branches, with which they coexist. This neuronal self-recognition is attained through families of cell recognition molecules which work as individual barcodes, allowing the discrimination of any other nearby branch as either "self" or "non-self".
Self-avoidance ensures that dendritic territories are covered completely and yet non-redundantly guaranteeing that branches achieve functionally appropriate coverage of input or output territories.
Neuronal communication requires the coordinated assembly of axons, dendrites, and synapses. Therefore, self-avoidance is necessary for proper neuronal wiring and postnatal development and, together with neuronal tiling (heteroneuronal avoidance), is a crucial spacing mechanism for patterning neural circuits that results in complete and nonredundant innervation of sensory or synaptic space.
History.
The concept of neuronal self-avoidance emerged about 50 years ago. The pioneer studies were performed in the leech, focusing on the central nervous system and developing mechanosensory neurons. Leeches from two species: "Hirudo medicinalis" and "Haementeria ghilianii", remained the main organism for the study of the question of neuronal self-recognition and self-avoidance. In this animal, the repeating segmental pattern of the nervous system along with the fact that neurons are relatively few in number, and many are large enough to be recognized allowed the experimental study of the general problem of neuronal specificity.
In 1968, through the mapping of mechanoreceptor axonal receptive fields in "H. medicilalis", Nicholls and Baylor revealed distinct types of boundaries between axons from the same or different types of neurons, and also between individual neurons. They observed that receptive fields were subdivided into discrete areas, innervated by the different branches of a single cell. These boundaries, unlike those between adjacent fields of different cells, were abrupt showing nearly no overlap. The authors then suggested a mechanism for the spatial arrangement of axons in which "a fiber might repel other branches more strongly if they arise from the same cell than if they come from a homologue, and not at all if they come from a cell with a different modality".
In 1976, Yau confirmed their findings and proposed that the branches of a cell recognized each other, therefore avoiding to grow into the same territory and establishing the discrete areas that Nicholls and Baylor observed. It was then clear that mechanosensory neurons, in leech, show self-avoidance: with the repulsion between branches originating from the same cell, but they did not showed class-avoidance, meaning that branches from the same type of neurons could overlap.
The phenomena was recognized but a lot remained unknown, including the term "Self-avoidance" which arises in 1982/1983 with the studies of Kramer.
In 1982, Kramer postulated that isoneuronal axons (axons growing from the same neuron), contrarily to heteroneuronal axons, avoid each other when growing on the same substrate (see Movie).
This was further explored, by other authors, the fact that this self-avoidance would require neurites to be able to distinguish between self and non-self, reinforcing the ideas of Yau.
In 1983 Kramer and Kuwada propose that this self-recognition of two growing axonal processes might be mediated by their filopodia, which appear to make mutual contacts. This idea was backed up by the studies of Goodman et al. (1982) in insect neurons, which postulated that filopodia played an important role in the recognition and choice of axonal growth pathways.
The conservation of the mechanism in invertebrates together with the fact that adult morphology of many neurons appears to satisfy the rule, suggested that non-overlap of isoneuronal processes could be a general phenomenon of neuronal development.
In 1985 empirical data was added by Kramer and Stent with the experimentally induced variations in the branching pattern through surgically preventing or delaying the outgrowth of the axon branches. As predicted by the proposal of self-avoidance, interference with the outgrowth of a field axon branch resulted in the spread of the axon branch of the other field into what normally was not a territory. Thus, neuronal self-avoidance does play a significant role in the development of mechanosensory receptive field structure.
In the late 1980s, the molecular machinery that could be the basis of the phenomena started to be unveiled. Receptors such as cell adhesion molecules of the cadherin and immunoglobulin super families, which mediate interactions between opposing cell surfaces, and integrins acting as receptors for extracellular matrix components were widely expressed on developing neurites.
In 1990, Macagno et al., integrated the results from several studies, once again emphasizing the evolutionary conservation of the overall phenomena: Leech neurons, like those of other invertebrates and those of vertebrates, undergo specific interactions during development which allow the definition of the adult morphologies and synaptic connections. That morphology reflects the developmental compromise between the potential of the neuron to grow and the constraints placed upon that growth by internal and external factors. Thus, the self-recognizing mechanism would be useful not only to self-avoidance but also as a means of individualization. During development, competition among neurons of the same type for a limited supply required for process growth and maintenance would occur, with one cell gaining space at the expense of others. Inhibitory interactions were also invoked, and this placed the phenomena of self-recognition in the bigger picture of the axon guidance process. Together, these studies led to the view that neural circuit assembly emerged as a result of a relatively small number of different signals and their receptors, some acting in a graded fashion and in different combinations.
In 1991, scientists became aware that self-avoidance was also present in non-neuronal cell types, such as leech comb cells, which might similarly form discrete domains. Later, this was also observed in mammalian astrocytes.
Wang and Macagno, in 1998, again recurring to "Hirudo medicinalis" mechanosensory neurons, performed an elegant experiment in order to try to answer the still remaining question: "How does a cell recognize self and respond by not growing over or along itself?"
The authors then proposed two general types of mechanisms: I) External signals: Sibling neurites display surface identifying molecular factors, unique to each cell, that are capable of homotypic binding and therefore repel sibling neurites, or II) Internal signals: synchronous cell activity, such as voltage, which is transmitted within the cell mediating a dynamic mechanism of sibling growth inhibition.
Contrarily to the first hypothesis, the second would require the continuity and communication between all parts of the cell for self-avoidance to occur.
So the experiment consisted of detaching one of the neurons dendrites and see how the remaining attached dendrites reacted towards the detached fragment, "do they still avoid overlapping?"
The result was that the detached branch would stop being recognized as "self" by the other branches of the neuronal, leading to dendrite overlap.
The clear conclusion of the study was that continuity between all parts of the neuron is critical for self-avoidance to operate. The authors then suggest various mechanisms that require continuity and could function as recognition signal, and thus might be the responsible ones, such as "electrical activity, active or passive, as well as the diffusion of cytoplasmic signals either passively or by fast axonal transport".
In the late 1990s and beyond, model organisms started to be used in the studies and the molecular mechanisms of self-avoidance started to be unraveled. In 1999 Wu and Maniatis discovered a striking organization of a large family of human neural protocadherin cell adhesion genes which formed a gene cluster encoding 58 protocadherins. The members of the protocadherin gene cluster were compelling candidates to provide the molecular code required for the maintenance of the self/non-self discrimination that led to self-avoidance. It was later (2012) confirmed, by Lefebvre et al., in a study with amacrine cells and Purkinje cells of "Mus musculus", that these proteins are expressed in different combinations in individual neurons, thus providing "barcodes" with that distinguish one neuron from another.
In 2000, Schmucker et al., through cDNA and genomic analyses of "Drosophila" dendritic arborization sensory neurons, the existence of multiple forms of "Down syndrome cell adhesion molecule (Dscam)" was revealed. The authors saw that alternative splicing could potentially generate more than 38,000 Dscam isoforms and hypothesized that this molecular diversity could contribute to the specificity of neuronal connectivity and thus, self-avoidance.
Together, the discoveries of the two large families of cell surface proteins encoded by the Dscam1 locus and the clustered protocadherin (Pcdh) loci opened the door to the numerous modern studies. The current studies take great advantage not only of the uprising of the molecular and genomic biology but also from the bioinformatics tools, developed since the 19th century.
Models, structures and development of self-avoidance.
Animal models.
Self-avoidance has been widely discussed amongst scientists and throughout time the experiments were done in several animal models.
The first experiments were done in leech. In 1981, Wässle tried to understand how retinal ganglion cells establish their dendritic territories in cats. Processes like dendritic tiling and self-avoidance are extremely important to correct development of neuronal structures, and in this specific case ganglion cells have to cover the retina to guarantee that every point of the visual space is actually "seen". He saw that cell bodies are arrayed in regular mosaic, and dendritic fields adapt to the available space. However, this hypothesis was based in mathematical models: Dirichlet model.
Perry and Linden (1982) were the first to present clear evidence of the dendritic "competition" in mice retina. Destruction of ganglion cells gives the chance to their neighboring cells to extend their dendritic projections. They proposed competition for synapses as the cause for equilibrium between growth and repulsion of dendrites.
Though mouse and Drosophila are the models currently used to construct a model of self-avoidance for vertebrates and invertebrates respectively, throughout time there are several examples of this phenomenon in other model and non-model species:
Trigeminal neurons in head skin exhibit a competitive behavior and only when one of them is completely removed, for example the left trigeminal ganglion, allows the right ganglion neurites to cross midline and innervate left side of the head. The correct innervation is due to repulsive nature of interactions between these movement detector neurites reinforcing all the anterior models of self-avoidance.
Retina grows throughout life by addition of new neurons at the margin and death of ganglion neurons in the center. Once again it is proved that each cell senses neighbor cells and can occupy space left by other.
Trigeminal neurons, developed 16hrs post fertilization, are part of the peripheral sensory system and detect thermal and mechanical stimuli in the skin. The "growth-and-repulsion" model arose from complex topographic restriction of growth cones between trigeminal and Rohon-Beard neurons.
Dscam mutants exhibit severely disorganized neural network and axon fasciculation.
Principal structures for self-avoidance studies.
The two major structures used in self-avoidance studies are the retinal ganglion cells (RGC) in mice and somatosensory neurons in "Drosophila". These structures are pointed as different molecular models because the principal molecule involved in self-avoidance is Dscam in invertebrates and Protocadherins in vertebrates.
Mouse retina.
Correct assembly of the components in mice retina is dependent of Dscam/DscamL1 correct expression to form mosaics of different cell type of RGC, soma spacing and dendrite arborization, thus ensuring the coverage of all visual area by each cell type and more specifically to inhibit excessive fasciculation and clumping of cell bodies in photoreceptors, rod bipolar cells (RBCs) and amacrine cells in visual system. The occurrence of correct stratification and connection with synapses tells us that Dscam knockout affects only the repulsive interactions and coverage of the dendritic arbors and functional bindings are maintained.
The actual main conclusions are based in the identification of different types of retinal neurons, each one with a different coverage factor value revealing graded degrees of homotypic dendritic repulsion. Developmental sequence accepted is 1) define number and spacing of cells, 2) controlled growth of branches and 3) fine-tune of dendritic tiling for maximal coverage of the structure. Experiments with mutant mice for "Math5" and "Brn3b" (responsible of degeneration of 95% and 80% of retinal ganglion cells, respectively) shows that removal of ganglion cells doesn't decrease the retinal ganglion cell types and that position of these cells isnot defined by dendritic homotypic interactions only, but for some kind of intrinsic genetic program.
Dendritic arborization neurons.
"Drosophila melanogaster" is the model for experiments in multiple dendritic (MD) neurons which compose the stereotyped pattern of peripheral nervous system. Dendritic arborization neurons are the major subtype of MD neurons group and presents highly branched dendrites underneath the epidermis. Sugimura et al. showed dendritic arborization (da) neurons that stabilize their branches shape in early larval stages and others that continue shaping throughout life cycle.
As other types of cells involved in processes dependent of self-recognition (like self-avoidance and tiling, See Figure-2) these da neurons can fill the empty spaces left by neighbor cells and this filling-in process is triggered by loss of local isoneural inhibitory contacts.
Larval eye.
Since "Drosophila" is one of the best studied models in mechanisms of neuronal self-recognition, we can find several results obtained in larval stages. One of the most remarkable examples is the incorrect development of dendritic arbors in the larval eye (Bolwig's organ) due to Dscam knockout mutation.
Development.
Numerous models and structures with different development timing and life cycles are used in studies of self-avoidance. Therefore, some conflicts arise when we try to define a strict development phase for the occurrence of these phenomena. The initial idea was that, in some early development point, neural cells contact with each other and organize their distribution, but several studies demonstrated that self-avoidance is also present in adult life.
To solve this question it would be ideal to monitor dendritic development of neurons from its birth till maturation inside whole-mount animals.
In "Drosophila", studies comprise both larval and adult phases, and number of hours after egg layer is determinant for correct construction of dendritic tiling in sensory neurons. Early in the pupal stage, those neurons prune all their dendrites. Later each neuron grows a completely new dendrite for adult function. While the dendrites are being remodeled, the axons stay largely intact and all these phases will be negatively impacted in case of interference with self-avoidance propriety.
Exons of Dscam domains can be differently expressed according to the life cycle phase of the fly. Exon 9 splicing is temporally regulated, with only a few exon 9 sequences contributing to early embryo isoforms and the remaining exon 9 possible sequences become more prevalent with age. These results prove that, independently of the thousands of isoforms that could be generated, the diversity continues to be temporally and spatially controlled.
In mouse retina the majority of ganglion cells are born at E17 (embryonic stage/day 17). At this age the retina has reached 25% of its mature size
Molecular basis of self-avoidance.
Cellular studies of self-avoidance imply that any underlying molecular mechanism must enforce robust and selective contact-dependent cell surface recognition only between sister branches, and must link recognition to changes in growth cone behavior. Recent studies to define the molecular basis of contact-dependent homotypic interactions led to the identification of two large families of cell-surface proteins encoded by the Drosophila Down syndrome cell adhesion molecule 1 ("Dscam1") locus and the clustered protocadherin (Pcdh) loci in mammals. These proteins, with diverse extracellular domains, and shared cytoplasmatic presumptive intracellular signaling domains, are able to provide diverse recognition specificities to a vast array of different neurites, endowing neurons with a unique cell-surface identity that allows neurons to distinguish self from non-self.
Additional self-surface receptors implicated in self-avoidance include the immunoglobulin superfamily member Turtle, which functions in some "Drosophila" da neurons to enforce terminal branch spacing.
Invertebrates.
DSCAM1.
Several studies have implicated "Drosophila" "Dscam1" in dendritic and axonal self-avoidance and process spacing in diverse neuronal populations, including mushroom body axons, olfactory projection neuron (PN) dendrites, and dendritic arborization (da) neuron dendrites
It is notable that the function of Dscam in invertebrates is both context and species-dependent, as the molecule has been shown to regulate repulsion, outgrowth, attraction/ adhesion, and synapse formation in different systems.
Dscam1 encodes an immunoglobulin (Ig) superfamily member which, in Drosophila, can generate up to 19,008 proteins with distinct ectodomains. In binding assays, Dscams show isoform-specific homophilic interactions, but little interaction occurs between different, yet closely related, isoforms.
Dscam1 controls self-avoidance.
Dscam1 mediated self-recognition is essential for self-avoidance between sister neurites
Hughes et al. (2007) reported that Dscam loss-of-function in da neurons caused excessive self-crossing of dendrites from the same neuron. Dscam over-expression forced the respective dendrites to segregate from each other. Based on these data, Dscam results in a lack of self-avoidance of sister dendrites. Therefore, the direct isoform-specific homophilic Dscam-Dscam interactions must result in signal transduction events that lead to repulsion of dendrites expressing identical Dscam isoforms. This conversion of an initial Dscam-dependent cell-surface interaction into a repulsive response that leads to dendrite separation in da neurons is supported by Matthews et al. (2007) in a study that demonstrated that the ectopic expression of identical Dscam isoforms on the dendrites of different cells promoted growth away from each other. The authors also suggest that identical Dscam isoforms expressed in two cell populations "in vitro" induced their aggregation in an isoform-specific manner, showing that Dscam provides cells with the ability to distinguish between different cell surfaces.
Moreover, expression of single Dscam1 molecules lacking most of their cytoplasmic tail prevented ectopic branch segregation and instead led to apparently stable adhesion between dendrites.
Combined, these results support a simple model for a direct role for Dscam in self-recognition in which identical Dscam ectodomains on the surfaces of isoneuronal dendrites recognize each other and induce a subsequent repulsive signal that is mediated by domains in the cytoplasmic tail (Figure 7).
Homophilic recognition provides the molecular basis for self-avoidance
To test whether homophilic binding of Dscam1 isoforms is required for self-avoidance, Wu and coworkers generated pairs of chimeric isoforms that bind to each other (heterophilic) but not to themselves (homophilic). These isoforms failed to support self-avoidance. By contrast, co-expression of complementary isoforms within the same neuron restored self-avoidance. These data establish that recognition between Dscam1 isoforms on opposing surfaces of neurites of the same cell provides the molecular basis for self-avoidance.
Diversity at the Dscam1 locus is essential for self-recognition.
Diversity of Dscam isoforms in individual neurons is not required for self-avoidance ...
In 2004, Zhan et al. published a study in which the function of Dscam diversity was explored by assessing the isoforms of Dscam expressed by the developing mushroom body (MB) neurons, as well as the ability of individual isoforms to rescue the Dscam loss-of-function phenotypes and the consequences of ectopic expression of single Dscam isoforms. They demonstrated that different subtypes of MB neurons express different arrays of Dscam isoforms and that loss of Dscam1 in these neurons leads to a failure in branch separation, a phenotype that can be rescued by the expression of single arbitrary isoforms in single neurons.
Also, in da neurons, single arbitrarily chosen isoforms rescued the Dscam1 null self-avoidance phenotype. These results lead to the conclusion that Dscam1 diversity is not required in individual neurons for self-avoidance.
... but diversity of Dscam isoforms expressed by neurons of different types is essential for discriminating between self and non-self neurites
To test whether sister branch segregation requires neighboring mushroom body axons to express different sets of Dscam isoforms, Hattori et al. (2009) reduced the entire repertoire of Dscam ectodomains to just a single isoform using homologous recombination and examined mushroom body morphology in "Dscamsingle" and control animals. In the majority of the mushroom bodies analyzed, one of the two lobes was completely absent and in the few remaining samples, one lobe was significantly thinner than the other. This dominant phenotype indicates that the defects do not result from the loss of any one isoform, but rather the presence of the same isoform on all axons.
These studies led to the conclusion that each neuron expresses a set of Dscam1 isoforms largely different from their neighbors and that it is crucial for neighboring neurons to express distinct Dscam isoforms, but the specific identity of the isoforms expressed in an individual neuron is unimportant, as long as sister branches express the identical set of isoforms to allow for the homotypic repulsion between them.
Thousands of isoforms are required for proper self-recognition
Later on, Hattori et al. (2009) took a genomic replacement strategy to generate mutant animals in which the number of potential Dscam1 isoforms was limited. Their goal was to determine how many isoforms were necessary to ensure that neurites do not inappropriately recognize and avoid non-self-neurites. Branching patterns improved as the potential number of isoforms increased, independently of the identity of the isoforms. In conclusion, the size of isoform pool required for robust discrimination between self and non-self is in the thousands.
In sum, isoform identity between branches of the same neuron leads to recognition via the extracellular region and repulsion mediated by the intracellular tail of Dscam1. As the Dscam1 isoforms expressed in different da neurons are likely to be different, dendrites of different da neurons do not inappropriately recognize non-self as self. Thus, Dscam1 proteins are required for self-avoidance and provide the molecular code by which neurites discriminate between self-dendrites and those of neighboring cells (Figure 7).
Vertebrates.
DSCAM and DSCAML1.
Self-avoidance has only recently been explored in the vertebrate brain development and mainly in the context of patterning neurites in the Inner plexiform layers (IPLs). In contrast to "Drosophila", mouse DSCAMs are typical cell surface molecules, lacking the massive alternative splicing of the fly Dscam1 orthologous undergoes. So although DSCAMs may retain a conserved function in mediating self-avoidance in vertebrates, the absence of molecular diversity makes it clear that they do not play a role in self-recognition.
Dscams act to negate cell-type-specific interactions rather than actively promoting repulsion in vertebrates' neurites
Considering that "Dscam" and "Dscaml1" have non-overlapping expression patterns in the mouse retina, with "Dscam" being expressed in a subset of amacrine cells and most retinal ganglion cells (RGC) and "Dscaml1" expressed in the rod circuit, Fuerst et al. (2009) examined retinal ganglion cell populations in "Dscam−/−" mice and, in addition, assessed retinal anatomy in the rod circuit using a gene-trap-knockout allele of "Dscaml1". In the absence of either gene, the cells that would normally express it showed excessive fasciculation of their dendrites and clumping of their cell bodies. These findings led to the conclusion that "Dscam" and "Dscaml1" prevent excessive adhesion, primarily by masking cell-type-specific adhesive interactions between dendrites of the same cell class, rather than actively promoting repulsion between them.
Thus, in the absence of diversity, mammalian DSCAMs do not provide cells with the ability to distinguish between their own processes and the processes of all other cells, including processes from cells of the same type. Instead, DSCAM acts to negate cell-type-specific interactions that are promoted by other recognition molecules.
Protocadherin.
More recent studies demonstrated that mice use a different family of cell recognition molecules: clustered Protocadherins (Pcdhs), in a fly Dscam1-like strategy to regulate self-avoidance. Although both clustered Pcdhs and Dscam1 genes generate families of proteins with diverse ectodomains joined to a common cytoplasmic domain, the mode of generating clustered Pcdhs and fly Dscam1 counterpart diversity is markedly different. Pcdhs diversity is largely generated by alternative promoter choice, as opposed to alternative splicing.
The number of Pcdhs isoforms varies between different vertebrate species, but in aggregate, there are typically on the order of 50 isoforms.
Isoform-specific homophilic recognition
Compelling evidence for discrete binding specificities of different clustered Pcdhs isoforms was uncovered in 2010 by Schreiner & Weiner, who verified that Pcdhs promote isoform-specific homophilic recognition. While the number of Pcdhs isoforms pales in comparison to the number of Dscam1 isoforms, hetero-oligomerization of Pcdhs markedly increases the number of discrete binding specificities encoded by the locus.
Pcdhs are required for self-avoidance
To seek roles of Pcdh-γs in self-avoidance, Lefebvre et al. (2012) focused on a retinal interneuron, the starburst amacrine cell (SAC), which expresses Pcdh-γs and exhibits dramatic dendritic self-avoidance. They used a Cre-Lox system to delete all the variable domains of the Pcdh-γ locus in the developing retina and verified that dendrites arising from a single SAC frequently crossed each other and sometimes formed loose bundles, similarly to the removal of Dscam1 from da neurons (Figure 8).
Pcdhs diversity is essential for self-recognition
Furthermore, Lefebvre and colleagues assessed the requirement for isoform diversity in Pcdh-γ-dependent self-avoidance. They demonstrated that single arbitrarily chosen isoforms rescued self-avoidance defects of Pcdh-γ mutant and that expression of the same isoform in neighboring SACs reduced the overlap between them.
Their results indicate that diversity appears to underlie self/non-self discrimination, presumably because neighboring neurons are unlikely to express the same isoforms and are therefore free to interact. Therefore, isoform diversity enables SACs to distinguish isoneuronal from heteroneuronal dendrites. As with "Dscam1", self-avoidance in SACs does not rely on a specific isoform, but rather requires that isoform usage differs among neighboring cells.
Thus, two phyla appear to have recruited different molecules to mediate similar, complex strategies for self-recognition, thereby promoting self-avoidance.


Arthur Ham

Arthur Worth Ham (20 February 1902 – 6 September 1992) was a prominent Canadian histologist. His textbook "Histology" is considered by many practitioners an indispensable reference.
Early life, education, and tennis.
Ham's early education came through Brantford Collegiate Institute and Vocational School. He followed with a medical degree (MB) from the University of Toronto which he completed in 1927. In 1925, Ham married Dorothy Carlotta Ross.
While interning at the Wellesley Hospital, Ham also pursued an active tennis career.
In 1928 and 1929, he doubles played for Canada's Davis Cup team, partnering Jack Wright. In '28 he and Wright lost 10-8 in the fifth set to the Japanese duo of Tamimo Abe and Teizo Toba, as Japan prevailed in this America Zone semi-final tie, 3-1. In 1929, Ham and Wright lost to the American team of John F. Hennessey and John Van Ryn, 1-6, 1-6, 6-1, 2-6. Canada lost this tie as well, an America Zone first round encounter, 0-5.
Histology.
In the early 1930s, Ham published his first series of major papers on the formation, maintenance, and destruction of bone within the body. The study of bone would be a theme to which Ham would return throughout his career.
The first edition of Ham's seminal histology text–titled simply "Histology"–was published in 1950.
Late career.
In 1951, Ham was elected a Fellow of the Royal Society of Canada.
Along with Harold E. Johns, Ham played a key role in the formation of the Department of Medical Biophysics at the University of Toronto. He served as the Department's first chair, from 1958 to 1960.
Within the Department of Anatomy, Ham assumed the Chair in 1965.
Ham was married in 1981 to Lotta Dempsey Fisher, following the death of his first wife. Ham was widowed once again in 1988.
The ninth edition of "Histology"–known almost universally as "Ham's Histology"–was published in 1987 by Ham jointly with David H. Cormack, Ph.D.


Venous heart

A venous heart is the type of heart in which only blood with CO₂ circulates. Venous hearts receive blood from veins and pumps it for oxygenation. This type of heart is generally found in fishes.
Structure.
Venous hearts only have the right side of heart, which contains an atrium (also known as auricle) and an ventricle. The heart is made of two chambers, unlike human hearts which have four chambers.
Blood circulation.
The blood circulation system via venous heart is close-looped. A venous heart is single circuit and the heart pumps blood all over the body with only a single loop. Deoxygenated blood circulates to the atrium from the body, and afterwards the deoxygenated blood moves to the ventricles from the atrium. Next, the blood reaches the gills for purification.
Like all hearts, venous hearts are also engaged in the distribution of nutrients, oxygen, hormones and other necessities to all parts of the body, and remove metabolic waste.


Jrk

dClock (clk) is a gene located on the 3L chromosome of "Drosophila melanogaster". Mapping and cloning of the gene indicates that it is the "Drosophila" homolog of the mouse gene CLOCK ("mClock"). The Jrk mutation disrupts the transcription cycling of "per" and "tim" and manifests dominant effects.
Discovery.
Discovered at Brandeis University in 1998, cloning the mutant "Jrk" led to the identification of the drosophila homolog of the mammalian Clock gene in DNA.
"Jrk" mutation.
"Jrk" is a mutation of a gene (not to be confused with JRKL ) discovered by Michael Rosbash and his colleagues in 1998. A common misconception is that the "Jrk" mutant gene is the "Drosophila" homolog of CLOCK ("mClock"), which disrupts cycling transcription of the "per" and "tim" genes. The "Jrk" mutation was discovered before "dClock", but it is a mutation of "dClock". "Jrk" is a semi-dominant third chromosome mutant displaying arrhythmic, or not rhythmic, locomotor behavior in constant darkness. It's been found that "Jrk" mutant flies are less robust to changes in the environment, such as temperature increases, than animals with the wild type "dClock" gene. The mutant flies also have differing light sensitivity and behavior patterns, suggesting that "dClock" is important in controlling coupled oscillators. The mutation in "dClock" that makes "Jrk" is from a premature stop codon that truncates the protein, deleting most of the putative C-terminal activation domain of the bHLH-PAS transcription factor. This is consistent with the mammalian "clock" mutant phenotype.
Structure.
Through complementation testing of "Jrk" with various deletions done by Allada et al., "Jrk" was found to be located on the left arm of chromosome 3, specifically at location 66A10-22.
Start site: 7,763,233
Stop site: 7,775,603
The dClock gene has a PAS domain between positions 90-156, and positions 255-321. These regions are important for allowing proteins to recognize and associate with one another, forming dimers. This is followed by a C-terminal PAC motif starting at position 327 and ending at 370. PAC motifs have been proposed to contribute to the PAS domain fold.
The gene also has a bHLH domain starting at position 21 and ending at position 71. This means that it binds specific DNA sequences, the E-box consensus sequence in this case, that regulate transcription. This domain is a 60 amino acid region with a DNA binding domain, which is followed by two amphipathic alpha-helices which are connected by a loop, forming the HLH motif. This region is also important in protein dimerization, which is necessary for DNA binding.
The gene has 5 transcripts, which encode for 4 unique polypeptides. It has 9 exons. The transcript of the gene is about 5000kB long, as determined through utilization of northern blot techniques. The polypeptide that the transcript encodes for has a reported size between 1015 and 1027 amino acids, and a molecular weight between 130 and 150kD.
Function.
Circadian clock.
In "Drosophila", there are two main players in the generation of circadian rhythms: the "period (per)" gene and "timeless (tim)". These two genes are responsible for the oscillations in protein levels, RNA levels, and transcription rates that occur in flies.
Another essential component of this circadian clock mechanism is that the PER protein contains a PAS domain, which has been demonstrated to mediate the interactions between transcription factors. These transcription factors also contain the well-characterized basic helix-loop-helix (bHLH) DNA-binding domains. Furthermore, in mice an E box (CACGTG) was discovered, which acts a binding site for some of the bHLH transcription factors, which includes bHLH-PAS transcription factors.
"Jrk" mutant phenotypes.
The mutant "Jrk" allele is a consequence of a point mutation, which is simply the insertion, deletion, or swapping of one nucleotide base in an mRNA sequence for another. This mutation exhibits a dominant negative effect, meaning that just one copy of it is enough to produce phenotypic deviation. The "Jrk" mutation deletes much of the gene that encodes for the glutamine (Q)-rich C terminus of the protein. This region is involved in transcriptional activation, which is necessary to allow mRNA to be transcribed from DNA in the nucleus. It can be achieved by utilizing ethyl methanesulfonate (EMS) as a mutagen. The mutation results in a cytosine being swapped for a thymine at the 7764959 position (C7764959T). This substitution causes what was initially encoded as a glutamine to be swapped for a premature stop codon, preventing further translation of the gene.
"Jrk" was identified as a homozygous mutant with completely arrhythmic locomotor behavior in constant darkness. Approximately half of all of the "Jrk" heterozygotes were arrhythmic, and those that did manifest a rhythm had a slightly longer period than the wild-type controls.
Researchers also observed that both PER and TIM levels are extremely low and non-cycling in homozygous "Jrk" flies, approximately equivalent to the trough levels of wild-type flies. In heterozygotes, PER and TIM cycle well, but the amplitude is reduced by approximately 50%, consistent with the clear effects on behavioral rhythmicity in these flies.
Mammalian homologs of "dClock".
The "Jrk" gene has a myriad of homologs throughout the natural world, with 642 orthologs and 3 paralogs. Mammal circadian systems contain the "Clock" gene which has been shown to be closely related to "dClock." Both have strikingly similar bHLH domains, which suggests that they associate with similar, if not identical, DNA targets. The PAS region is also highly conserved between drosophila and mice. This suggests that both "Jrk" and its mouse homolog have conserved heterodimeric partners.
Mammalian mutations in the Clock gene have been found to result in autism spectrum disorder, schizophrenia, attention‐deficit/hyperactivity disorder, major depressive disorder, bipolar disorder, anxiety disorder, and substance use disorder.


Tetanic fade

Tetanic fade refers to the diminishing muscle twitch response from an evoked potential stimulation of muscle under the effect of either a non-depolarizing neuromuscular blocking agent, or a muscle that is under a phase 2 depolarizing neuromuscular blocking agent.
Overview.
In order to transduce an excitatory signal to the muscle, an indication must transduce from the presynaptic neuron's axon terminal, travel across the synaptic cleft and be received correctly in the post synaptic muscle tissue's motor end plate to produce the desired effect, at the right intensity. The signal that leaves the presynaptic neuron is in the form of Acetylcholine (Ach), a molecule that is released from stored vesicles at the terminal end of the neuron. Ach travels across the space of the synaptic cleft, to an Ach receptors on the sarcolemma of the motor end plate. shortly following its effect, the ach is being degraded by the enzymatic acetylcholinesterase.
The Ach receptor is a ligand gated channel that once bound to Ach, goes through a conformational change that allows the flow of calcium, sodium, and potassium down their respective gradient. In large enough ion change an electrochemical potential will form, which is called an endplate potential (EPP). The EPP signal will be propagated through the motor end plate and to the T-tubules to affect the muscle filaments via sodium channels. These sodium channels have a brief activation window, after which they are inactivated until the end plate potential is restored to baseline levels.
Responses to tetany in muscle tissue.
Without neuromuscular blocking agent.
Tetany in evoked stimulus, as defined in Morgan & Mikhail's Clinical Anesthesiology as a ~5 seconds of sustained stimulus of between 50 and a 100 Hz. The reaction of muscle tissue to stimulus under no neuromuscular blockade should be equal in intensity throughout the stimulus, The first muscle twitch and last should be of roughly equal magnitude. Clinically it will present as equal muscle contraction throughout the duration of muscle stimulation.
Under non-depolarizing neuromuscular blocking agent.
Non-depolarizing neuromuscular blocking agents (ie Rocuronium, Vecuronium) interact with Ach receptor without activating the channel, as well as preventing the binding of acetylcholine to it. This blocks the signal propagation from the presynaptic neuron, and the severs the transduction of the excitatory signal from the synaptic cleft.
Muscle tissue treated with a non-depolarizing neuromuscular blocking agents will produce an indicative response in the form of a tetanic fade, a diminishing response to tetanic stimulation where the initial intensity will be the highest, and the following ones will show lower and lower strength of response.
A some data suggest that this response is due to effect of non-depolarizing neuromuscular blocking agents on the presynaptic nerve, leading to lower acetylcholine secreted to the cleft during the tetanic stimulation. In normal muscle tissue release of Ach works to stimulate more release of Ach from the presynaptic neuron's axon in a positive feedback manner, in tissue under a non-depolarizing neuromuscular blocking agent greatly diminished the levels of Ach that are released into the synaptic cleft.
Under depolarizing neuromuscular blocking agent.
Depolarizing neuromuscular blocking agents (ie Succinylcholine) employ their effect by binding to the ach receptor and activating it, unlike acetylcholine though, the drug is not rapidly degraded by acetylcholinesterase. Succinylcholine propagates in high concentration for longer duration until it is degraded in the plasma and liver by a different enzyme (pseudocholinesterase). This continues to activate the Ach receptor, and prevents sodium channels from recovering to their active state. This leads to muscle relaxation and termed phase 1 block, clinically it will present as a diminished twitch response during tetanic stimulation.
Phase 1 block does not show fade under tetanic stimulation. With further administration of depolarizing neuromuscular blocking agent, an effect that is similar to the response of muscle to non-depolarizing neuromuscular blocking agents can be observed. This response, termed phase 2 block, will demonstrate similar fade under tetanic stimulation, a diminishing response to tetanic stimulation where the initial response will be the strongest, and will produce lower and lower response intensity.
References.


Lepidocyrtus

Lepidocyrtus is a genus of slender springtails in the family Entomobryidae. There are at least 30 described species in "Lepidocyrtus".


Albert Nelson, 6th Earl Nelson

Albert Francis Joseph Horatio Nelson, 6th Earl Nelson, FRGS, FRSA, FZS (2 September 1890 – 23 June 1957), styled Viscount Merton between 1947 and 1951, was a British peer. He was the great-great grand nephew of Admiral Lord Nelson.
He was the oldest son of The Hon. Edward Nelson (who later succeeded as The 5th Earl Nelson in 1948) and Geraldine Cave; he was educated at Downside School and Maredsous Abbey. He fought in World War I in the Australian Imperial Force. A lecturer in astronomy and anthropology, he was appointed Fellow of the Royal Astronomical Society (FRAS), Fellow of the Royal Geographical Society (FRGS) and Fellow of the Royal Society of Arts (FRSA). He authored two books: Life in the Universe (1953), and There IS Life on Mars (1955).
On 16 January 1924, he married Amelia Cooper (died 1937), a Californian and widow of John C. Scott. They were divorced in 1925. In 1927, he married Marguerite Helen O'Sullivan (died 6 February 1969) in Scotland. They were married again in England in 1942. The Earl died childless in 1957 and was succeeded by his brother.


Subcutaneous tissue of perineum

The subcutaneous tissue of perineum (or superficial perineal fascia) is a layer of subcutaneous tissue surrounding the region of the perineal body.
The superficial fascia of this region consists of two layers, superficial and deep.