Anaphylaxis

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Anaphylaxis 

 

Anaphylaxis
Other names	Anaphylactoid, anaphylactic shock
Angioedema of the face such that the boy cannot open his eyes. This reaction was caused by an allergen exposure.
Specialty	Allergy and immunology
Symptoms	Itchy rash, throat swelling, numbness, shortness of breath, lightheadedness,
Usual onset	Over minutes to hours
Causes	Insect bites, foods, medications
Diagnostic method	Based on symptoms
Differential diagnosis	Allergic reaction, angioedema, asthma exacerbation, carcinoid syndrome
Treatment	Epinephrine, intravenous fluids
Frequency	0.05–2%

Anaphylaxis is a serious allergic reaction that is rapid in onset and may cause death. It typically causes more than one of the following: an itchy rash, throat or tongue swelling, shortness of breath, vomiting, lightheadedness, low blood pressure. These symptoms typically come on over minutes to hours.

Common causes include insect bites and stings, foods, and medications. Other causes include latex exposure and exercise; cases may also occur without an obvious reason. The mechanism involves the release of mediators from certain types of white blood cells triggered by either immunologic or non-immunologic mechanisms. Diagnosis is based on the presenting symptoms and signs after exposure to a potential allergen.

The primary treatment of anaphylaxis is epinephrine injection into a muscle, intravenous fluids, then placing the person "in a reclining position with feet elevated to help restore normal blood flow". Additional doses of epinephrine may be required. Other measures, such as antihistamines and steroids, are complementary. Carrying an epinephrine autoinjector and identification regarding the condition is recommended in people with a history of anaphylaxis.

Worldwide, 0.05–2% of the population is estimated to experience anaphylaxis at some point in life. Rates appear to be increasing. It occurs most often in young people and females. About 99.7% of people hospitalized with anaphylaxis in the United States survive. The term comes from the Ancient Greek: ἀνά, romanized: ana, lit. 'against', and the Ancient Greek: φύλαξις, romanized: phylaxis, lit. 'protection'.

Signs and symptoms

Signs and symptoms of anaphylaxis

Anaphylaxis typically presents many different symptoms over minutes or hours with an average onset of 5 to 30 minutes if exposure is intravenous and 2 hours if from eating food. The most common areas affected include: skin (80–90%), respiratory (70%), gastrointestinal (30–45%), heart and vasculature (10–45%), and central nervous system (10–15%) with usually two or more being involved.

Skin

Urticaria and flushing on the back of a person with anaphylaxis

Symptoms typically include generalized hives, itchiness, flushing, or swelling (angioedema) of the afflicted tissues. Those with angioedema may describe a burning sensation of the skin rather than itchiness. Swelling of the tongue or throat occurs in up to about 20% of cases. Other features may include a runny nose and swelling of the conjunctiva. The skin may also be blue tinged because of lack of oxygen.

Respiratory

Respiratory symptoms and signs that may be present include shortness of breath, wheezes, or stridor. The wheezing is typically caused by spasms of the bronchial muscles while stridor is related to upper airway obstruction secondary to swelling. Hoarseness, pain with swallowing, or a cough may also occur.

Cardiovascular

While a fast heart rate caused by low blood pressure is more common, a Bezold–Jarisch reflex has been described in 10% of people, where a slow heart rate is associated with low blood pressure. A drop in blood pressure or shock (either distributive or cardiogenic) may cause the feeling of lightheadedness or loss of consciousness. Rarely very low blood pressure may be the only sign of anaphylaxis.

Coronary artery spasm may occur with subsequent myocardial infarction, dysrhythmia, or cardiac arrest. Those with underlying coronary disease are at greater risk of cardiac effects from anaphylaxis. The coronary spasm is related to the presence of histamine-releasing cells in the heart.

Other

Gastrointestinal symptoms may include severe crampy abdominal pain, diarrhea, and vomiting. There may be confusion, a loss of bladder control or pelvic pain similar to that of uterine cramps. Dilation of blood vessels around the brain may cause headaches. A feeling of anxiety or of "impending doom" has also been described.

Causes

Anaphylaxis can occur in response to almost any foreign substance. Common triggers include venom from insect bites or stings, foods, and medication. Foods are the most common trigger in children and young adults while medications and insect bites and stings are more common in older adults. Less common causes include: physical factors, biological agents such as semen, latex, hormonal changes, food additives such as monosodium glutamate and food colors, and topical medications. Physical factors such as exercise (known as exercise-induced anaphylaxis) or temperature (either hot or cold) may also act as triggers through their direct effects on mast cells. Events caused by exercise are frequently associated with cofactors such as the ingestion of certain foods or taking an NSAID. During anesthesia, neuromuscular blocking agents, antibiotics, and latex are the most common causes. The cause remains unknown in 32–50% of cases, referred to as "idiopathic anaphylaxis." Six vaccines (MMR, varicella, influenza, hepatitis B, tetanus, meningococcal) are recognized as a cause for anaphylaxis, and HPV may cause anaphylaxis as well.

Food

Many foods can trigger anaphylaxis; this may occur upon the first known ingestion. Common triggering foods vary around the world. In Western cultures, ingestion of or exposure to peanuts, wheat, nuts, certain types of seafood like shellfish, milk, and eggs are the most prevalent causes. Sesame is common in the Middle East, while rice and chickpeas are frequently encountered as sources of anaphylaxis in Asia. Severe cases are usually caused by ingesting the allergen, but some people experience a severe reaction upon contact. Children can outgrow their allergies. By age 16, 80% of children with anaphylaxis to milk or eggs and 20% who experience isolated anaphylaxis to peanuts can tolerate these foods.

Medication

Any medication may potentially trigger anaphylaxis. The most common are β-lactam antibiotics (such as penicillin) followed by aspirin and NSAIDs. Other antibiotics are implicated less frequently. Anaphylactic reactions to NSAIDs are either agent specific or occur among those that are structurally similar meaning that those who are allergic to one NSAID can typically tolerate a different one or different group of NSAIDs. Other relatively common causes include chemotherapy, vaccines, protamine and herbal preparations. Some medications (vancomycin, morphine, x-ray contrast among others) cause anaphylaxis by directly triggering mast cell degranulation.

The frequency of a reaction to an agent partly depends on the frequency of its use and partly on its intrinsic properties. Anaphylaxis to penicillin or cephalosporins occurs only after it binds to proteins inside the body with some agents binding more easily than others. Anaphylaxis to penicillin occurs once in every 2,000 to 10,000 courses of treatment, with death occurring in fewer than one in every 50,000 courses of treatment. Anaphylaxis to aspirin and NSAIDs occurs in about one in every 50,000 persons. If someone has a reaction to penicillin, his or her risk of a reaction to cephalosporins is greater but still less than one in 1,000. The old radiocontrast agents caused reactions in 1% of cases, while the newer lower osmolar agents cause reactions in 0.04% of cases.

Venom

Venom from stinging or biting insects such as Hymenoptera (ants, bees, and wasps) or Triatominae (kissing bugs) may cause anaphylaxis in susceptible people. Previous reactions that are anything more than a local reaction around the site of the sting, are a risk factor for future anaphylaxis; however, half of fatalities have had no previous systemic reaction.

Risk factors

People with atopic diseases such as asthma, eczema, or allergic rhinitis are at high risk of anaphylaxis from food, latex, and radiocontrast agents but not from injectable medications or stings. One study in children found that 60% had a history of previous atopic diseases, and of children who die from anaphylaxis, more than 90% have asthma. Those with mastocytosis or of a higher socioeconomic status are at increased risk. The longer the time since the last exposure to the agent in question, the lower the risk.

Pathophysiology

Anaphylaxis is a severe allergic reaction of rapid onset affecting many body systems. It is due to the release of inflammatory mediators and cytokines from mast cells and basophils, typically due to an immunologic reaction but sometimes non-immunologic mechanism.

Interleukin (IL)–4 and IL-13 are cytokines important in the initial generation of antibody and inflammatory cell responses to anaphylaxis.

Immunologic

In the immunologic mechanism, immunoglobulin E (IgE) binds to the antigen (the foreign material that provokes the allergic reaction). Antigen-bound IgE then activates FcεRI receptors on mast cells and basophils. This leads to the release of inflammatory mediators such as histamine. These mediators subsequently increase the contraction of bronchial smooth muscles, trigger vasodilation, increase the leakage of fluid from blood vessels, and cause heart muscle depression. There is also a non-immunologic mechanism that does not rely on IgE, but it is not known if this occurs in humans.

Non-immunologic

Non-immunologic mechanisms involve substances that directly cause the degranulation of mast cells and basophils. These include agents such as contrast medium, opioids, temperature (hot or cold), and vibration. Sulfites may cause reactions by both immunologic and non-immunologic mechanisms.

Diagnosis

Anaphylaxis is diagnosed on the basis of a person's signs and symptoms. When any one of the following three occurs within minutes or hours of exposure to an allergen there is a high likelihood of anaphylaxis:

1. Involvement of the skin or mucosal tissue plus either respiratory difficulty or a low blood pressure causing symptoms
2. Two or more of the following symptoms after a likely contact with an allergen:

   a. Involvement of the skin or mucosa

   b. Respiratory difficulties

   c. Low blood pressure

   d. Gastrointestinal symptoms

3. Low blood pressure after exposure to a known allergen

Skin involvement may include: hives, itchiness or a swollen tongue among others. Respiratory difficulties may include: shortness of breath, stridor, or low oxygen levels among others. Low blood pressure is defined as a greater than 30% decrease from a person's usual blood pressure. In adults a systolic blood pressure of less than 90 mmHg is often used.

During an attack, blood tests for tryptase or histamine (released from mast cells) might be useful in diagnosing anaphylaxis due to insect stings or medications. However these tests are of limited use if the cause is food or if the person has a normal blood pressure, and they are not specific for the diagnosis.

Classification

There are three main classifications of anaphylaxis.

• Anaphylactic shock is associated with systemic vasodilation that causes low blood pressure which is by definition 30% lower than the person's baseline or below standard values.
• Biphasic anaphylaxis is the recurrence of symptoms within 1–72 hours after resolution of an initial anaphylactic episode. Estimates of incidence vary, between less than 1% and up to 20% of cases. The recurrence typically occurs within 8 hours. It is managed in the same manner as anaphylaxis.
• Anaphylactoid reaction, non-immune anaphylaxis, or pseudoanaphylaxis, is a type of anaphylaxis that does not involve an allergic reaction but is due to direct mast cell degranulation. Non-immune anaphylaxis is the current term used by the World Allergy Organization with some recommending that the old terminology no longer be used.

Allergy testing

Skin allergy testing being carried out on the right arm

 

Patch test

Allergy testing may help in determining the trigger. Skin allergy testing is available for certain foods and venoms. Blood testing for specific IgE can be useful to confirm milk, egg, peanut, tree nut and fish allergies.

Skin testing is available to confirm penicillin allergies, but is not available for other medications. Non-immune forms of anaphylaxis can only be determined by history or exposure to the allergen in question, and not by skin or blood testing.

Differential diagnosis

It can sometimes be difficult to distinguish anaphylaxis from asthma, syncope, and panic attacks. Asthma however typically does not entail itching or gastrointestinal symptoms, syncope presents with pallor rather than a rash, and a panic attack may have flushing but does not have hives. Other conditions that may present similarly include: scrombroidosis and anisakiasis.

Post-mortem findings

In a person who died from anaphylaxis, autopsy may show an "empty heart" attributed to reduced venous return from vasodilation and redistribution of intravascular volume from the central to the peripheral compartment. Other signs are laryngeal edema, eosinophilia in lungs, heart and tissues, and evidence of myocardial hypoperfusion. Laboratory findings could detect increased levels of serum tryptase, increase in total and specific IgE serum levels.

Prevention

See also: Allergen immunotherapy

Avoidance of the trigger of anaphylaxis is recommended. In cases where this may not be possible, desensitization may be an option. Immunotherapy with Hymenoptera venoms is effective at desensitizing 80–90% of adults and 98% of children against allergies to bees, wasps, hornets, yellowjackets, and fire ants. Oral immunotherapy may be effective at desensitizing some people to certain food including milk, eggs, nuts and peanuts; however, adverse effects are common. For example, many people develop an itchy throat, cough, or lip swelling during immunotherapy. Desensitization is also possible for many medications, however it is advised that most people simply avoid the agent in question. In those who react to latex it may be important to avoid cross-reactive foods such as avocados, bananas, and potatoes among others.

Management

Anaphylaxis is a medical emergency that may require resuscitation measures such as airway management, supplemental oxygen, large volumes of intravenous fluids, and close monitoring. Passive leg raise may also be helpful in the emergency management.

Administration of epinephrine is the treatment of choice with antihistamines and steroids (for example, dexamethasone) often used as adjuncts. A period of in-hospital observation for between 2 and 24 hours is recommended for people once they have returned to normal due to concerns of biphasic anaphylaxis.

Epinephrine

An old version of an EpiPen auto-injector

Epinephrine (adrenaline) (1 in 1,000) is the primary treatment for anaphylaxis with no absolute contraindication to its use. It is recommended that an epinephrine solution be given intramuscularly into the mid anterolateral thigh as soon as the diagnosis is suspected. The injection may be repeated every 5 to 15 minutes if there is insufficient response. A second dose is needed in 16–35% of episodes with more than two doses rarely required. The intramuscular route is preferred over subcutaneous administration because the latter may have delayed absorption. It is recommended that after diagnosis and treatment of anaphylaxis, the patient should be kept under observation in an appropriate clinical setting until symptoms have fully resolved. Minor adverse effects from epinephrine include tremors, anxiety, headaches, and palpitations.

People on β-blockers may be resistant to the effects of epinephrine. In this situation if epinephrine is not effective intravenous glucagon can be administered which has a mechanism of action independent of β-receptors.

If necessary, it can also be given intravenously using a dilute epinephrine solution. Intravenous epinephrine, however, has been associated both with dysrhythmia and myocardial infarction. Epinephrine autoinjectors used for self-administration typically come in two doses, one for adults or children who weigh more than 25 kg and one for children who weigh 10 to 25 kg.

Adjuncts

Antihistamines (both H1 and H2), while commonly used and assumed effective based on theoretical reasoning, are poorly supported by evidence. A 2007 Cochrane review did not find any good-quality studies upon which to base recommendations and they are not believed to have an effect on airway edema or spasm. Corticosteroids are unlikely to make a difference in the current episode of anaphylaxis, but may be used in the hope of decreasing the risk of biphasic anaphylaxis. Their prophylactic effectiveness in these situations is uncertain. Nebulized salbutamol may be effective for bronchospasm that does not resolve with epinephrine. Methylene blue has been used in those not responsive to other measures due to its presumed effect of relaxing smooth muscle.

Preparedness

People prone to anaphylaxis are advised to have an allergy action plan. Parents are advised to inform schools of their children's allergies and what to do in case of an anaphylactic emergency. The action plan usually includes use of epinephrine autoinjectors, the recommendation to wear a medical alert bracelet, and counseling on avoidance of triggers. Immunotherapy is available for certain triggers to prevent future episodes of anaphylaxis. A multi-year course of subcutaneous desensitization has been found effective against stinging insects, while oral desensitization is effective for many foods.

Prognosis

In those in whom the cause is known and prompt treatment is available, the prognosis is good. Even if the cause is unknown, if appropriate preventive medication is available, the prognosis is generally good. If death occurs, it is usually due to either respiratory (typically asphyxia) or cardiovascular causes (shock), with 0.7–20% of cases causing death. There have been cases of death occurring within minutes. Outcomes in those with exercise-induced anaphylaxis are typically good, with fewer and less severe episodes as people get older.

Epidemiology

The number of people who get anaphylaxis is 4–100 per 100,000 persons per year, with a lifetime risk of 0.05–2%. About 30% of people get more than one attack. Exercise-induced anaphylaxis affects about 1 in 2000 young people.

Rates appear to be increasing: the numbers in the 1980s were approximately 20 per 100,000 per year, while in the 1990s it was 50 per 100,000 per year. The increase appears to be primarily for food-induced anaphylaxis. The risk is greatest in young people and females.

Anaphylaxis leads to as many as 500–1,000 deaths per year (2.7 per million) in the United States, 20 deaths per year in the United Kingdom (0.33 per million), and 15 deaths per year in Australia (0.64 per million). Another estimate from the United States puts the death rate at 0.7 per million. Mortality rates have decreased between the 1970s and 2000s. In Australia, death from food-induced anaphylaxis occur primarily in women while deaths due to insect bites primarily occur in males. Death from anaphylaxis is most commonly triggered by medications.

History

The term aphylaxis was coined by French physiologist Charles Richet in 1902 in the sense "lack of protection". Richet himself later changed the term to anaphylaxis on grounds of euphony. The term is from the Greek ἀνά-, ana-, meaning "against", and φύλαξις, phylaxis, meaning "protection". In his experiments, Richet injected a dog with sea anemone (Actinia) toxin in an attempt to protect it. Although the dog had previously tolerated the toxin, on re-exposure, three weeks later with the same dose, it developed fatal anaphylaxis. Thus instead of inducing tolerance (prophylaxis), when lethal responses resulted from previously tolerated doses, he coined the word a (without) phylaxis (protection). He was subsequently awarded the Nobel Prize in Physiology or Medicine for his work on anaphylaxis in 1913. The phenomenon itself, however, has been described since ancient times.

Research

There are ongoing efforts to develop sublingual epinephrine to treat anaphylaxis. Subcutaneous injection of the anti-IgE antibody omalizumab is being studied as a method of preventing recurrence, but it is not yet recommended.

Asian giant hornet

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Asian_giant_hornet 

 

Asian giant hornet
Vespa mandarinia form "magnifica". Private collection, F. Turetta.
Conservation status
Not evaluated (IUCN 3.1)
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Insecta
Order:	Hymenoptera
Family:	Vespidae
Genus:	Vespa
Species:	V. mandarinia
Binomial name
Vespa mandarinia Smith, 1852
Synonyms
Vespa magnifica Smith, 1852 Vespa japonica Radoszkowski, 1857 Vespa bellona Smith, 1871 Vespa magnifica var. latilineata Cameron, 1903 Vespa mandarina Dalla Torre, 1894 (misspelling) Vespa mandarinia nobilis Sonan, 1929 Vespa magnifica sonani Matsumura, 1930

The Asian giant hornet (Vespa mandarinia), including the color form referred to as the Japanese giant hornet, is the world's largest hornet. It is native to temperate and tropical East Asia, South Asia, Mainland Southeast Asia, and parts of the Russian Far East. It was also found in the Pacific Northwest of North America in late 2019 with a few more additional sightings in 2020, and nests found in 2021, prompting concern that it could become an invasive species.

Asian giant hornets prefer to live in low mountains and forests, while almost completely avoiding plains and high-altitude climates. V. mandarinia creates nests by digging, co-opting pre-existing tunnels dug by rodents, or occupying spaces near rotted pine roots. It feeds primarily on larger insects, colonies of other eusocial insects, tree sap, and honey from honey bee colonies. The hornet has a body length of 45 millimetres (1+3⁄4 inches), a wingspan around 75 mm (3 in), and a stinger 6 mm (1⁄4 in) long, which injects a large amount of potent venom.

Although the scientific literature and official government sources continue to refer to this species by its established common name, the mainstream media have taken to using the nickname "murder hornet".

Taxonomy and phylogeny

V. mandarinia is a species in the genus Vespa, which comprises all true hornets. Along with seven other species, V. mandarinia is a part of the V. tropica species group, defined by the single notch located on the apical margin of the seventh gastral sternum of the male. The most closely related species within the species group is V. soror. The triangular shape of the apical margin of the clypeus of the female is diagnostic, the vertex of both species is enlarged, and the shape of the apex of the aedeagus is distinct and similar. Division of the genus into subgenera has been attempted in the past, but has been abandoned, due to the anatomical similarity among species and because behavioral similarity is not associated with phylogeny.

As of 2012, three subspecies were recognized: V. m. mandarinia, V. m. magnifica, and V. m. nobilis. The former subspecies referred to as V. m. japonica has not been considered valid since 1997. The most recent revision in 2020 eliminated all of the subspecies rankings entirely, with "japonica", "magnifica", and "nobilis" now relegated to informal non-taxonomic names for different color forms.

Description

Head detail

 

Hornet specimen held in a human hand to illustrate its size

Regardless of sex, the hornet's head is a light shade of orange and its antennae are brown with a yellow-orange base. Its eyes and ocelli are dark brown to black. V. mandarinia is distinguished from other hornets by its pronounced clypeus and large genae. Its orange mandible contains a black tooth that it uses for digging. The thorax is dark brown, with two grey wings varying in span from 35 to 76 mm (1+3⁄8 to 3 in). Its forelegs are brighter than the mid and hind legs. The base of the forelegs is darker than the rest. The abdomen alternates between bands of dark brown or black, and a yellow-orange hue (consistent with its head color). The sixth segment is yellow. Its stinger is typically 6 mm (1⁄4 in) long and delivers a potent venom that, in cases of multiple hornets stinging simultaneously, can kill a human.

Queens and workers

The queens are considerably larger than workers. Queens can exceed 50 mm (2 in), while workers are between 35 and 40 mm (1+3⁄8 and 1+5⁄8 in). The reproductive anatomy is consistent between the two, but workers do not reproduce.

Drones

Drones (males) are similar to females, and can attain 38 millimetres (1+1⁄2 in) in length, but lack stingers. This is a consistent feature among the Hymenoptera.

Larvae

Larvae spin a silk cocoon when they complete development and are ready to pupate. Larval silk proteins have a wide variety of potential applications due to their wide variety of potential morphologies, including the native fiber form, but also sponge, film, and gel.

Misidentifications

Reports of this species from other parts of the world appear to be erroneous identifications of other introduced hornet species, such as V. orientalis in several locations around the world, V. velutina in Europe, and the European hornet (V. crabro) in the eastern United States.

The Eastern Cicada Killer (Sphecius speciosus) also lives in the eastern United States. It is a large digger wasp which can reach 2 inches (5.1 cm) in length, and has also been mistaken for the Asian Giant Hornet.

Distribution

Ecological distribution

V. mandarinia is primarily a forest dweller. When it does live in urban landscapes however, V. mandarinia is highly associated with green space. It is the most dependent upon green space of the Vespas (with V. analis the least). Extremely urbanized areas thus provide a refuge for V. analis where V. mandarinia – its predator – is entirely absent.

Geographic distribution

The Asian giant hornet

Asia

The Asian giant hornet can be found in

• Russia – Primorsky Krai, Khabarovsky Krai (southern part only) and Jewish AO region
• Korea (where it is called 장수말벌 "general officer hornet")
• Mainland China
• Taiwan (simplified Chinese: 大虎头蜂; traditional Chinese: 大虎頭蜂; lit. 'giant tiger head bee')
• Laos
• Thailand
• Cambodia
• Myanmar
• Vietnam
• Nepal
• India
• Sri Lanka
• Japan – It is common in Japan. It prefers rural areas where it can find trees to nest in and is known as the ōsuzumebachi (オオスズメバチ(大雀蜂), literally, "giant sparrow bee"). At least by 2008, some popular and sensationalist media outlets in Japan also began referring to this wasp as satsujin suzumebachi (殺人スズメバチ, literally, "murder hornet").

North America

The first confirmed sightings of the Asian giant hornet in North America were confirmed in 2019 and has mainly been concentrated in the Vancouver area, with nests also discovered in neighboring Whatcom County, Washington, in the United States.

• In August 2019, three hornets were found in Nanaimo on Vancouver Island, and a large nest was found and destroyed shortly thereafter;
• At the end of September, a worker was reported in Blaine, Washington.
• Another worker was found in Blaine in October;
• On 8 December 2019, another worker was found in Blaine;
• Two specimens were collected in May 2020, one from Langley, British Columbia, about 13 kilometres (8 miles) north of Blaine, and one from Custer, Washington, 14 km (9 mi) southeast of Blaine.
• One queen sighting on 6 June 2020, from Bellingham, Washington, 24 km (15 mi) south of Custer
• An unmated queen was trapped on 14 July 2020, near Birch Bay, Washington, 10 km (6 mi) west of Custer.
• A male hornet was captured in Custer, Washington on 29 July 2020.
• A hornet of unknown caste was reported on 18 August 2020, in Birch Bay, and another was trapped in the same area the following day.
• Three hornets were seen (and two killed) southeast of Blaine on 21 and 25 September 2020, and three more were found in the same area on 29 and 30 September, prompting officials to report that attempts were underway to pinpoint and destroy a nest believed to be in the area.
• On 23 October 2020, the Washington State Department of Agriculture announced that a nest was found 2.5 metres (8.3 ft) above ground in a cavity of a tree in Blaine, with dozens of hornets entering and leaving. The nest was eradicated the next day, including the immediate discovery and removal of about 100 hornets. After further analysis, it was determined that the nest had contained about 500 live specimens, including about 200 queens. Some of these specimens were sent to the Smithsonian Institution to become a part of the NMNH Biorepository permanent cryogenic collection. It was announced that several undiscovered live nests were also believed to exist within Washington State, when considering the captures of individual hornets in Birch, Blaine, and Custer that were all relatively far from the discovered nest. However, cautious optimism was expressed by officials saying that it might still be possible to eradicate the hornets before they can become established in the area. A Canadian official said that although individual specimens had been found in Canada and some nests were suspected to exist there, the presence there seemed to be only in near-border regions, and the center of the invasion seemed to be in Washington State.
• On 2 November 2020, one individual was found in Abbotsford, BC. As a result the BC government asked Abbotsford beekeepers and residents to report any sightings.
• On 7 November 2020, a queen was found in Aldergrove, BC.
• On 11 August 2021, a nest was discovered in Whatcom County, Washington near Blaine, only 2 miles (3.2 km) from the nest WSDA eradicated in 2020. This nest was destroyed two weeks later on 25 August, before it could produce new queens.
• In September 2021, two more nests were found near Blaine, in the vicinity of the nest found in August, and a "potential sighting" was reported from near Everson, some 25 miles east of Blaine.

A mitochondrial DNA analysis was performed to determine the maternal population(s) ancestral to the British Columbia and Washington introduced populations. The high dissimilarity between these two was similar to the mutual distances between each of the Chinese, Japanese, and Korean native populations suggesting the specimens collected in 2019 were from two different maternal populations, Japanese in BC and South Korean in Washington. This suggests that two simultaneous introductions of the Asian giant hornet occurred in North America within about 80 km (50 mi) of one another within a few months.

In April 2020, authorities in Washington asked members of the public to be alert and report any sightings of these hornets, which are expected to become active in April if they are in the area. If they become established, it is claimed that the hornets "could decimate bee populations in the United States and establish such a deep presence that all hope for eradication could be lost." A "full-scale hunt" for the species by the WSDA was then underway. Two assessment models of their potential to spread from their present location on the US–Canada border suggested that they could spread northward into coastal British Columbia and Southeast Alaska, and southward as far as southern Oregon. The USDA's Agricultural Research Service is engaged in lure/attractant development and molecular genetics research, both as part of its normal research mission but also to further the near-term eradication goal in Washington State.

In 2020, the United States Congress considered specific legislation to eradicate V. mandarinia including a proposal by the Interior Secretary, the Fish and Wildlife Director, and the other relevant agencies, which has been introduced as an amendment to the appropriations omnibus. British Columbia Agriculture is prepared for a "long fight" lasting years, if necessary. One advantage humans will have is the lack of diversity of such an invasive population – leaving the hornets less prepared for novel environments and challenges.

On June 4, 2021 a dead, desiccated male was found near Marysville, Snohomish County, Washington State and reported to WSDA. Its different, more reddish color form immediately suggested yet another parental population than the Japanese and Korean already known, but DNA testing was needed. USDA APHIS (Animal and Plant Health Inspection Service) did the analysis and a few days later together with WSDA confirmed it was of a third, unrelated population. The discovery of a male in June is "perplexing" given that the earliest male emergence in 2020 was July, which was already earlier than normal for the home range. This and its desiccated state indicate it did not emerge in 2021 at all but is instead a dead specimen which had already emerged in a previous year.

Nesting

V. mandarinia nests in low mountain foothills and lowland forests. As a particularly dominant species, no efforts are directed toward conserving V. mandarinia or its habitats, as they are common in areas of low human disturbance. Unlike other species of Vespa, V. mandarinia almost exclusively inhabits subterranean nests. In a study of 31 nests, 25 were found around rotten pine roots, and another study found only 9 of 56 nests above ground. Additionally, rodents, snakes, or other burrowing animals previously made some of the tunnels. The depth of these nests was between 6 and 60 cm (2 and 24 in). The entrance at the ground surface varies in length from 2 to 60 cm (1 to 24 in) either horizontally, inclined, or vertically. The queens that found the nest prefer narrow cavities.

Nests of V. mandarinia typically lack a developed envelope. During the initial stages of development, the envelope is in an inverted-bowl shape. As the nest develops, one to three rough sheets of combs are created. Often, single primordial combs are created simultaneously and then fused into a single comb.

A system of one main pillar and secondary pillars connects the combs. Nests usually have four to seven combs. The top comb is abandoned after summer and left to rot. The largest comb is at the middle to bottom portion of the nest. The largest combs created by V. mandarinia measured 49.5 by 45.5 cm (19+1⁄2 by 18 in) with 1,192 cells (no obstacles, circular) and 61.0 by 48.0 cm (24 by 19 in) (elliptical; wrapped around a root system).

Colony cycle

The nesting cycle of V. mandarinia is fairly consistent with that of other eusocial insects. Six phases occur in each cycle.

Pre-nesting period

Inseminated and uninseminated queens enter hibernation following a cycle. They first appear in early to mid-April and begin feeding on the sap of Quercus (oak) trees. Although this timing is consistent among hornets, V. mandarinia dominates the order, receiving preference for premium sap sources. Among the V. mandarinia queens is a dominance hierarchy. The top-ranked queen begins feeding, while the other queens form a circle around her. Once the top queen finishes, the second-highest-ranking queen feeds. This process repeats until the last queen feeds at a poor hour.

Solitary, cooperative and polyethic periods

Inseminated queens start to search for nesting sites in late April. The uninseminated queens do not search for nests, since their ovaries never fully develop. They continue to feed, but then disappear in early July.

An inseminated queen begins to create relatively small cells in which she raises around 40 small workers. Workers do not begin to work outside of the hive until July. Queens participate in activities outside the hive until mid-July, when they stay inside the nest and allow workers to do extranidal activities. Early August marks a fully developed nest, containing three combs holding 500 cells and 100 workers. After mid-September, no more eggs are laid and the focus shifts to caring for larvae. The queens die in late October.

Dissolution and hibernating period

male Asian giant hornet

Males and new queens take on their responsibilities in mid-September and mid-October, respectively. During this time, their body color becomes intense and the weight of the queens increase about 20%. Once the males and queens leave the nest, they do not return. In V. mandarinia, males wait outside the nest entrance until the queens emerge. Once the queens emerge, males intercept them in midair, bring them to the ground, and copulate from 8 to 45 seconds. After this episode, the males return to the entrance for a second chance, while the now-mated queen leaves to hibernate. Many queens (up to 65%) attempt to fight off the males and leave unfertilized, at least temporarily. After this episode, pre-hibernating queens are found in moist, subterranean habitats.

When sexed individuals emerge, workers shift their focus from protein and animal foods to carbohydrates. The last sexed individuals to emerge may die of starvation.

Sting

The stinger of the Asian giant hornet is about 6 mm (1⁄4 in) long, which is about 4.5 mm (3⁄16 in) longer than that of a honeybee.

Venom

That stinger injects an especially potent venom that contains, like many bee and wasp venoms, a cytolytic peptide (specifically, a mastoparan) that can damage tissue by stimulating phospholipase action, in addition to its own phospholipase. Masato Ono, an entomologist at Tamagawa University, described the sensation of being stung as feeling "like a hot nail being driven into my leg". Besides using their stingers to inject venom, Asian giant hornets are apparently able to spray venom into a person's eyes under certain circumstances, with one report in 2020 from Japan of long-term damage, though the exact extent of actual visual impairment still remains unassessed.

The venom contains a neurotoxin called mandaratoxin, a single-chain polypeptide with a molecular weight around 20 kDa. While a single wasp cannot inject a lethal dose, multiple stings can be lethal even to people who are not allergic if the dose is sufficient; but allergy to the venom greatly increases the risk of death. Tests involving mice found that the venom falls short of being the most lethal of all wasp venom, having an LD₅₀ of 4.0 mg/kg. (In comparison, the deadliest wasp venom (at least to laboratory mice) by weight belongs to V. luctuosa at 1.6 mg/kg.) The potency of the V. mandarinia sting is due, rather, to the relatively large amount of venom injected.

Immunogenicity

There is insufficient evidence to believe that prophylactic immunotherapy for the venom of other Vespidae will prevent allergic reaction to V. mandarinia venom, because of wide differences in venom chemistry.

Effects on humans

Since 2001, the yearly human death toll caused by stings of bees, wasps and hornets in Japan has been ranging between 12 and 26. Since this number also includes deaths caused by bees, wasps, and other hornet species, the number of deaths caused by Asian giant hornets is likely to be much lower.

Advice in China is that people stung more than 10 times should seek medical help, and require emergency treatment for more than 30 stings. The stings can cause kidney failure. In 2013, stings by Asian giant hornets killed 41 people and injured more than 1,600 people in Shaanxi, China.

One source claims that most people who sought medical attention for a sting entered anaphylaxis before or during the medical session, and that deaths from envenomation are primarily related to anaphylactic shock or cardiac arrest. Either way, certainly some venom fractions are immunogenic and some are cardiotoxic to mammals. Deaths have occurred as a result of multiple organ failure, typically after a large number of stings. Sting victims that experience life-threatening organ failure commonly exhibit signs of skin hemorrhaging and necrosis, though in patients without organ failure, these symptoms are very rare. The two likely reasons for skin hemorrhaging and necrosis are an inability to effectively neutralize the venom, or unusually potent venom toxicity for that set of stings. In either case, for a small number of victims, these stings lead to multiple organ injury. While not all such victims displayed lesions or necrosis, a strong correlation existed between the number of stings and the severity of injury. Those who died, on average, were stung 59 times (with a standard error of 12), while those who survived suffered only, on average, 28 stings (with a standard error of four, and a p = 0.01).

Parasites

The strepsipteran Xenos moutoni is a common parasite among Vespa species. In a study of parasites among species of Vespa, 4.3% of V. mandarinia females were parasitized. Males were not stylopized (parasitization by stylopid strepsipterans, such as Xenos moutoni) at all. The major consequence of being parasitized is the inability to reproduce, and stylopized queens follow the same fate as uninseminated queens. They do not search for an area to create a new colony and feed on sap until early July, when they disappear. In other species of Vespa, males also have a chance of being stylopized. The consequences between the two sexes are similar, as neither sex is able to reproduce.

Communication and perception

V. mandarinia uses both visual and chemical cues as a means of navigating itself and others to the desired location. Scent marking was discussed as a way for hornets to direct other members of the colony to a food source. Even with antennae damage, V. mandarinia was able to navigate itself. It was unable to find its destination only when vision impairment was induced. This implies that while chemical signaling is important, visual cues play an equally important role in guiding individuals. Other behaviors include the formation of a "royal court" consisting of workers that lick and bite the queen, thereby ingesting her pheromones.

These pheromones could directly communicate between the queen and her court or indirectly between her court and other workers due to the ingested pheromones. This is merely speculation, as no direct evidence has been collected to suggest the latter. V. mandarinia communicates acoustically, as well. When larvae are hungry, they scrape their mandibles against the walls of the cell. Furthermore, adult hornets click their mandibles as a warning to other creatures that encroach upon their territory.

Scent marking

V. mandarinia is the only species of social wasp known to apply a scent to direct its colony to a food source. The hornet secretes the chemical from the sixth sternal gland, also known as the van der Vecht's gland. This behavior is observed during autumnal raids after the hornets begin hunting in groups instead of individually. The ability to apply scents may have arisen because the Asian giant hornet relies heavily on honey bee colonies as its main food source. A single hornet is unable to take on an entire colony of honey bees because species such as Apis cerana have a well-organized defense mechanism: the honey bees swarm one wasp and flutter their wings to heat up the hornet and raise carbon dioxide to a lethal level. So, organized attacks are much more effective and easily devastate a colony of tens of thousands of honey bees.

Interspecies dominance

In an experiment observing four different species of Vespa, including V. ducalis, V. crabro, V. analis, and V. mandarinia, V. mandarinia was the dominant species. Multiple parameters were set to determine this. The first set parameter observed interaction-mediated departures, which are defined as scenarios wherein one species leaves its position due to the arrival of a more dominant individual. The proportion of interaction-mediated departures was the lowest for V. mandarinia. Another measured parameter was attempted patch entry. Over the observed time, conspecifics (interactions with the same species) resulted in refused entry far more than heterospecifics (interactions with different species). Lastly, when feeding at sap flows, fights between these hornets, Pseudotorynorrhina japonica, Neope goschkevitschii, and Lethe sicelis were observed, and once more V. mandarinia was the most dominant species. In 57 separate fights, one loss was observed to Neope goschkevitschii, giving V. mandarinia a win rate of 98.3%. Based on interaction-mediated departures, attempted patch entry, and interspecific fights, V. mandarinia is the most dominant species.

Diet

An Asian giant hornet feeding on a mantis

The Asian giant hornet is intensely predatory; it hunts medium- to large-sized insects, such as bees, other hornet species, and mantises. The latter are favored targets in late summer and fall. Large insects such as mantises are key protein sources to feed queen and drone larvae. Workers forage to feed their larvae, and since their prey can include crop pests, the hornets are sometimes regarded as beneficial. This hornet often attacks both colonies of other Vespa species (V. simillima being the usual prey species) and honey bee hives to obtain the adults, pupae, and larvae as food for their own larvae; sometimes, they also cannibalize each other's colonies. A single scout, sometimes two or three, cautiously approaches the hive, producing pheromones to lead its nest-mates to the hive. The hornets can devastate a colony of honey bees, especially if it is the introduced western honey bee; a single hornet can kill as many as 40 bees per minute due to its large mandibles, which can quickly strike and decapitate prey. The honey bees' stings are ineffective because the hornets are five times their size and heavily armored. Only a few hornets (under 50) can exterminate a colony of tens of thousands of bees in a few hours. The hornets can fly up to 100 km (60 mi) in a single day, at speeds up to 40 km/h (25 mph). The smaller Asian hornet similarly predates on honey bees, and has been spreading throughout Europe.

Hornet larvae, but not adults, can digest solid protein; the adult hornets can only drink the juices of their victims, and they chew their prey into a paste to feed to their larvae. The workers dismember the bodies of their prey to return only the most nutrient-rich body parts, such as flight muscles, to the nest. Larvae of predatory social vespids generally (not just Vespa) secrete a clear liquid, sometimes referred to as Vespa amino acid mixture, the exact amino acid composition of which varies considerably from species to species, and which they produce to feed the adults on demand.

Native honey bees

A defensive ball of Japanese honey bees (Apis cerana japonica) in which two hornets (V. simillima xanthoptera) are engulfed, incapacitated, heated and eventually killed; this sort of defense is also used against the Asian giant hornet.

Beekeepers in Japan attempted to introduce western honey bees (Apis mellifera) for the sake of their high productivity. Western honey bees have no innate defense against the hornets, which can rapidly destroy their colonies. Although a handful of Asian giant hornets can easily defeat the uncoordinated defenses of a western honey bee colony, the Japanese honey bee (Apis cerana japonica) has an effective strategy. When a hornet scout locates and approaches a Japanese honey bee hive, she emits specific pheromonal hunting signals. When the Japanese honey bees detect these pheromones, 100 or so gather near the entrance of the nest and set up a trap, keeping the entrance open. This permits the hornet to enter the hive. As the hornet enters, a mob of hundreds of bees surrounds it in a ball, completely covering it and preventing it from reacting effectively. The bees violently vibrate their flight muscles in much the same way as they do to heat the hive in cold conditions. This raises the temperature in the ball to the critical temperature of 46 °C (115 °F). In addition, the exertions of the honey bees raise the level of carbon dioxide (CO₂) in the ball. At that concentration of CO₂, they can tolerate up to 50 °C (122 °F), but the hornet cannot survive the combination of high temperature and high carbon dioxide level. Some honey bees do die along with the intruder, much as happens when they attack other intruders with their stings, but by killing the hornet scout, they prevent it from summoning reinforcements that would wipe out the entire colony.

Detailed research suggests this account of the behavior of the honey bees and a few species of hornets is incomplete and that the honey bees and the predators are developing strategies to avoid expensive and mutually unprofitable conflict. Instead, when honey bees detect scouting hornets, they transmit an "I see you" signal that commonly warns off the predator. Another defence used by Apis cerana is speeding up dramatically when returning to the colony, to avoid midair attacks.

Diet in North America

WSDA found V. mandarinia to be predating on cluster fly, orange legged drone fly, bristle fly, bronze birch borer beetle, western honey bee, western yellowjacket, german yellowjacket, aerial yellowjacket, bald faced hornet, European paper wasp, golden paper wasp, paddle-tailed darner dragonfly, shadow darner dragonfly, large yellow underwing moth, blinded sphinx moth, and red admiral butterfly (Vanessa atalanta). They had also eaten cow's meat but WSDA assumes this to be beef from a hamburger.

Pollination

V. mandarinia is among the diurnal pollinators of the obligate plant parasite, the plant Mitrastemon yamamotoi.

Extermination methods

As of 1973, six different methods were used to control hornets in Japan. Though these methods decrease damage done by V. mandarinia, controlling them entirely is difficult.

Beating

Hornets are crushed with wooden sticks with flat heads. Hornets do not counterattack when they are in the bee-hunting phase or the hive-attack phase ("slaughter"), but they aggressively guard a beehive once they kill the defenders and occupy it. The biggest expenditure in this method is time, as the process is inefficient.

Nest removal

Applying poisons or fires at night is an effective way of exterminating a colony. The most difficult part about this tactic is finding the subterranean nests. The most common method of discovering nests is giving a piece of frog or fish meat attached to a cotton ball to a wasp and following it back to its nest. With V. mandarinia, this is particularly difficult considering its common home flight radius of 1–2 kilometres (0.62–1.24 mi). V. mandarinia travels up to 8 kilometres (5.0 mi) away from the nest.

For the rare nest that is up in a tree, wrapping the tree in plastic and vacuuming the hornets out is used.

Bait traps

Bait traps can be placed in apiaries. The system consists of multiple compartments that direct the hornet into a one-sided hole which is difficult to return through once it is in the cul-de-sac compartment, an area located at the top of the box which honey bees can escape from through a mesh opening, but wasps cannot due to their large size. Baits used to attract the hornets include a diluted millet jelly solution or a crude sugar solution with a mixture of intoxicants, vinegar, or fruit essence.

WSDA has been using plastic bottle traps, baited with fruit juice and added alcohol. The alcohol is used because it repels bees but not V. mandarinia, thus reducing the bycatch.

Mass poisoning

Hornets at the apiary are captured and fed a sugar solution or bee that has been poisoned with malathion. The toxin is expected to spread through trophallaxis. This method is good in principle, but has not been tested extensively.

Trapping at hive entrances

The trap is attached to the front of beehives. The effectiveness of the trap is determined by its ability to capture hornets while allowing honey bees to escape easily. The hornet enters the trap and catches a bee. When it tries to fly back through the entrance of the hive, it hits the front of the trap. The hornet flies upwards to escape and enters the capture chamber, where the hornets are left to die. Some hornets find a way to escape the trap through the front, so these traps can be very inefficient.

Protective screens

As explained in the trapping section, if met by resistance, hornets lose the urge to attack and instead retreat. Different measures of resistance include weeds, wire, or fishing nets or limiting the passage size so only honey bees can make it through. Experienced hornets catch on and eventually stay on these traps, awaiting the arrival of bees. The best method of controlling hornets is to combine protective screens with traps.

Human consumption

In some Japanese mountain villages, the nests are excavated and the larvae are considered a delicacy when fried. In the central Chūbu region, these wasps are sometimes eaten as snacks or an ingredient in drinks. The grubs are often preserved in jars, pan-fried or steamed with rice to make a savory dish called hebo-gohan. The adults are fried on skewers, stinger and all, until the body becomes crunchy.

Economic impact

If V. mandarinia reaches all suitable habitat in North America, control costs in the United States will be over US$113.7 million/year (possibly significantly higher).

Agricultural impact

If V. mandarinia reaches all suitable habitat in North America, bee products would bring in US$11.98 ± 0.64 million less/year, and bee-pollinated crops would produce US$101.8 million less/year. New York, Massachusetts, Pennsylvania, Connecticut, North Carolina, New Jersey, and Virginia would be the states most severely affected. By region New England would be worst hit, and to a lesser degree the entire northeast and the entirety of eastern North America. New England would become by far the greatest concentration of V. mandarinia in the world, far surpassing the original introduction site (the Pacific Northwest), and even its home range of East Asia. Alfalfa/other hays, apples, grapes, tobacco, cotton, and blueberries would be the crops most severely affected.

Living fossil

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Living_fossil 

The coelacanths were thought to have gone extinct 66 million years ago, until a living specimen belonging to the order was discovered in 1938.

A living fossil is an extant taxon that cosmetically resemble ancestral species known only from the fossil record. To be considered a living fossil, the fossil species must be old relative to the time of origin of the extant clade. Living fossils commonly are of species-poor lineages, but they need not be. While the body plan of a living fossil remains superficially similar, it is never the same species as the remote ancestors it resembles, because genetic drift would inevitably change its chromosomal structure.

Living fossils exhibit stasis (also called "bradytely") over geologically long time scales. Popular literature may wrongly claim that a "living fossil" has undergone no significant evolution since fossil times, with practically no molecular evolution or morphological changes. Scientific investigations have repeatedly discredited such claims.

The minimal superficial changes to living fossils are mistakenly declared as an absence of evolution, but they are examples of stabilizing selection, which is an evolutionary process—and perhaps the dominant process of morphological evolution.

Characteristics

Fossil and living ginkgos

170 million-year-old fossil Ginkgo leaves

 

Living Ginkgo biloba plant

Living fossils have two main characteristics, although some have a third:

1. Living organisms that are members of a taxon that has remained recognisable in the fossil record over an unusually long time span.
2. They show little morphological divergence, whether from early members of the lineage, or among extant species.
3. They tend to have little taxonomic diversity.

The first two are required for recognition as a living fossil status; some authors also require the third, others merely note it as a frequent trait.

Such criteria are neither well-defined nor clearly quantifiable, but modern methods for analyzing evolutionary dynamics can document the distinctive tempo of stasis. Lineages that exhibit stasis over very short time scales are not considered living fossils; what is poorly-defined is the time scale over which the morphology must persist for that lineage to be recognized as a living fossil.

The term "living fossil" is much misunderstood in popular media in particular, in which it often is used meaninglessly. In professional literature the expression seldom appears and must be used with far more caution, although it has been used inconsistently.

One example of a concept that could be confused with "living fossil" is that of a "Lazarus taxon", but the two are not equivalent; a Lazarus taxon (whether a single species or a group of related species) is one that suddenly reappears, either in the fossil record or in nature, as if the fossil had "come to life again". In contrast to "Lazarus taxa", a living fossil in most senses is a species or lineage that has undergone exceptionally little change throughout a long fossil record, giving the impression that the extant taxon had remained identical through the entire fossil and modern period. Because of the mathematical inevitability of genetic drift, though, the DNA of the modern species is necessarily different from that of its distant, similar-looking ancestor. They almost certainly would not be able to cross-reproduce, and are not the same species.

The average species turnover time, meaning the time between when a species first is established and when it finally disappears, varies widely among phyla, but averages about 2–3 million years. A living taxon that had long been thought to be extinct could be called a Lazarus taxon once it was discovered to be still extant. A dramatic example was the order Coelacanthiformes, of which the genus Latimeria was found to be extant in 1938. About that there is little debate — however, whether Latimeria resembles early members of its lineage sufficiently closely to be considered a living fossil as well as a Lazarus taxon has been denied by some authors in recent years.

Coelacanths disappeared from the fossil record some 80 million years ago (upper Cretaceous) and, to the extent that they exhibit low rates of morphological evolution, extant species qualify as living fossils. It must be emphasised that this criterion reflects fossil evidence, and is totally independent of whether the taxa had been subject to selection at all, which all living populations continuously are, whether they remain genetically unchanged or not.

This apparent stasis, in turn, gives rise to a great deal of confusion — for one thing, the fossil record seldom preserves much more than the general morphology of a specimen. To determine much about its physiology is seldom possible; not even the most dramatic examples of living fossils can be expected to be without changes, no matter how persistently constant their fossils and the extant specimens might seem. To determine much about noncoding DNA is hardly ever possible, but even if a species were hypothetically unchanged in its physiology, it is to be expected from the very nature of the reproductive processes, that its non-functional genomic changes would continue at more-or-less standard rates. Hence, a fossil lineage with apparently constant morphology need not imply equally constant physiology, and certainly neither implies any cessation of the basic evolutionary processes such as natural selection, nor reduction in the usual rate of change of the noncoding DNA.

Some living fossils are taxa that were known from palaeontological fossils before living representatives were discovered. The most famous examples of this are:

• Coelacanthiform fishes (2 species)
• Metasequoia, the dawn redwood discovered in a remote Chinese valley (1 species)
• glypheoid lobsters (2 species)
• mymarommatid wasps (10 species)
• eomeropid scorpionflies (1 species)
• jurodid beetles (1 species)
• soft sea urchins (59 species)

All the above include taxa that originally were described as fossils but now are known to include still-extant species.

Other examples of living fossils are single living species that have no close living relatives, but are survivors of large and widespread groups in the fossil record. For example:

• Ginkgo biloba
• Syntexis libocedrii, the cedar wood wasp
• Dinoflagellates (typified on coccoid dinocysts: occasionally calcareous cell remnants)

All of these were described from fossils before later found alive.

The fact that a living fossil is a surviving representative of an archaic lineage does not imply that it must retain all the "primitive" features (plesiomorphies) of its ancestral lineage. Although it is common to say that living fossils exhibit "morphological stasis", stasis, in the scientific literature, does not mean that any species is strictly identical to its ancestor, much less remote ancestors.

Some living fossils are relicts of formerly diverse and morphologically varied lineages, but not all survivors of ancient lineages necessarily are regarded as living fossils. See for example the uniquely and highly autapomorphic oxpeckers, which appear to be the only survivors of an ancient lineage related to starlings and mockingbirds.

Evolution and living fossils

The term living fossil is usually reserved for species or larger clades that are exceptional for their lack of morphological diversity and their exceptional conservatism, and several hypotheses could explain morphological stasis on a geologically long time-scale. Early analyses of evolutionary rates emphasized the persistence of a taxon rather than rates of evolutionary change. Contemporary studies instead analyze rates and modes of phenotypic evolution, but most have focused on clades that are thought to be adaptive radiations rather than on those thought to be living fossils. Thus, very little is presently known about the evolutionary mechanisms that produce living fossils or how common they might be. Some recent studies have documented exceptionally low rates of ecological and phenotypic evolution despite rapid speciation. This has been termed a "non-adaptive radiation" referring to diversification not accompanied by adaptation into various significantly different niches. Such radiations are explanation for groups that are morphologically conservative. Persistent adaptation within an adaptive zone is a common explanation for morphological stasis. The subject of very low evolutionary rates, however, has received much less attention in the recent literature than that of high rates

Living fossils are not expected to exhibit exceptionally low rates of molecular evolution, and some studies have shown that they do not. For example, on tadpole shrimp (Triops), one article notes, "Our work shows that organisms with conservative body plans are constantly radiating, and presumably, adapting to novel conditions.... I would favor retiring the term ‘living fossil’ altogether, as it is generally misleading."

The question posed by several recent studies pointed out that the morphological conservatism of coelacanths is not supported by paleontological data. In addition, it was shown recently that studies concluding that a slow rate of molecular evolution is linked to morphological conservatism in coelacanths are biased by the a priori hypothesis that these species are ‘living fossils’. Accordingly, the genome stasis hypothesis is challenged by the recent finding that the genome of the two extant coelacanth species L. chalumnae and L. menadoensis contain multiple species-specific insertions, indicating transposable element recent activity and contribution to post-speciation genome divergence. Such studies, however, challenge only a genome stasis hypothesis, not the hypothesis of exceptionally low rates of phenotypic evolution.

History

The term was coined by Charles Darwin in his On the Origin of Species from 1859, when discussing Ornithorhynchus (the platypus) and Lepidosiren (the South American lungfish):

... All fresh-water basins, taken together, make a small area compared with that of the sea or of the land; and, consequently, the competition between fresh-water productions will have been less severe than elsewhere; new forms will have been more slowly formed, and old forms more slowly exterminated. And it is in fresh water that we find seven genera of Ganoid fishes, remnants of a once preponderant order: and in fresh water we find some of the most anomalous forms now known in the world, as the Ornithorhynchus and Lepidosiren, which, like fossils, connect to a certain extent orders now widely separated in the natural scale. These anomalous forms may almost be called living fossils; they have endured to the present day, from having inhabited a confined area, and from having thus been exposed to less severe competition.

Other definitions

Long-enduring

Elephant shrews resemble the extinct Leptictidium of Eocene Europe.

A living taxon that lived through a large portion of geologic time.

Queensland lungfish (Neoceratodus fosteri) is an example of an organism that meets this criterion. Fossils identical to modern Queensland lungfish have been dated at over 100 million. Modern Queensland lungfish have existed as a species for almost 30 million years. The contemporary Nurse shark, a threatened species has existed for more than 112 million years making this species one of the oldest if not actually the oldest extant vertebrate species.

Resembles ancient species

A living taxon morphologically and/or physiologically resembling a fossil taxon through a large portion of geologic time (morphological stasis).

Retains many ancient traits

More primitive trapdoor spiders, such as this female Liphistius sp., have segmented plates on the dorsal surface of the abdomen and cephalothorax, a character shared with scorpions, making it probable that after the spiders diverged from the scorpions, the earliest unique ancestor of trapdoor species was the first to split off from the lineage that contains all other extant spiders.

A living taxon with many characteristics believed to be primitive.

This is a more neutral definition. However, it does not make it clear whether the taxon is truly old, or it simply has many plesiomorphies. Note that, as mentioned above, the converse may hold for true living fossil taxa; that is, they may possess a great many derived features (autapomorphies), and not be particularly "primitive" in appearance.

Relict population

Any one of the above three definitions, but also with a relict distribution in refuges.

Some paleontologists believe that living fossils with large distributions (such as Triops cancriformis) are not real living fossils. In the case of Triops cancriformis (living from the Triassic until now), the Triassic specimens lost most of their appendages (mostly only carapaces remain), and they have not been thoroughly examined since 1938.

Low diversity

Any of the first three definitions, but the clade also has a low taxonomic diversity (low diversity lineages).

Oxpeckers are morphologically somewhat similar to starlings due to shared plesiomorphies, but are uniquely adapted to feed on parasites and blood of large land mammals, which has always obscured their relationships. This lineage forms part of a radiation that includes Sturnidae and Mimidae, but appears to be the most ancient of these groups. Biogeography strongly suggests that oxpeckers originated in eastern Asia and only later arrived in Africa, where they now have a relict distribution.

The two living species thus seem to represent an entirely extinct and (as Passerida go) rather ancient lineage, as certainly as this can be said in the absence of actual fossils. The latter is probably due to the fact that the oxpecker lineage never occurred in areas where conditions were good for fossilization of small bird bones, but of course, fossils of ancestral oxpeckers may one day turn up enabling this theory to be tested.

Operational definition

An operational definition was proposed in 2017, where a 'living fossil' lineage has a slow rate of evolution and occurs close to the middle of morphological variation (the centroid of morphospace) among related taxa (i.e. a species is morphologically conservative among relatives). The scientific accuracy of the morphometric analyses used to classify tuatara as a living fossil under this definition have been criticised however, which prompted a rebuttal from the original authors.