CONTENTS

keywords

discovery [edit]

Coronaviruses were first discovered in the 1960s.[8] The earliest ones discovered were infectious bronchitis virus in chickens and two viruses from the nasal cavities of human patients with the common cold that were subsequently named human coronavirus 229E and human coronavirus OC43.[9] Other members of this family have since been identified, including SARS-CoV in 2003, HCoV NL63 in 2004, HKU1 in 2005, MERS-CoV in 2012, and SARS-CoV-2 (formerly known as 2019-nCoV) in 2019.

Most of these have involved serious respiratory tract infections.

 

etymology [edit]

The name "coronavirus" is derived from Latin corona, meaning "crown" or "wreath", itself a borrowing from Greek κορώνη korṓnē, "garland, wreath". The name refers to the characteristic appearance of virions (the infective form of the virus) by electron microscopy, which have a fringe of large, bulbous surface projections creating an image reminiscent of a crown or of a solar corona.[citation needed] This morphology is created by the viral spike peplomers, which are proteins on the surface of the virus .

 

morphology [edit]

Cross-sectional model of a coronavirus

Coronaviruses are large pleomorphic spherical particles with bulbous surface projections.[10] The diameter of the virus particles is around 120 nm.[11] The envelope of the virus in electron micrographs appears as a distinct pair of electron dense shells.[12]

The viral envelope consists of a lipid bilayer where the membrane (M), envelope (E) and spike (S) structural proteins are anchored.[13] A subset of coronaviruses (specifically the members of Betacoronavirus subgroup A) also have a shorter spike-like surface protein called hemagglutinin esterase (HE).[5] Inside the envelope, there is the nucleocapsid, which is formed from multiple copies of the nucleocapsid (N) protein, which are bound to the positive-sense single-stranded RNA genome in a continuous beads-on-a-string type conformation.[11][14] The genome size for coronaviruses ranges from approximately 27 to 34 kilobases.[7] The lipid bilayer envelope, membrane proteins, and nucleocapsid protect the virus when it is outside the host cell.[15]

The spike protein's interaction with its complement host cell receptor is central in determining the tissue tropism, infectivity, and species range of the virus.[16][17] Infection begins when the virus enters the host organism and the spike protein attaches to its complementary host cell receptor. The SARS coronavirus, for example, attaches to the angiotensin-converting enzyme 2 (ACE2) receptor.[18] After attachment, a protease of the host cell cleaves and activates the receptor-attached spike protein. Depending on the host protease this allows cell entry through endocytosis or direct fusion of the viral envelop with the host membrane.[19] The spike protein's interaction with its complement host cell receptor is central in determining the tissue tropism, infectivity, and species range of the virus.[16][17] Infection begins when the virus enters the host organism and the spike protein attaches to its complementary host cell receptor. 

infection [edit]

The monarch butterfly or simply monarch (Danaus plexippus) is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae.[4] Other common names depending on region include milkweed, common tiger, wanderer, and black veined brown.[5] It may be the most familiar North American butterfly, and is considered an iconic pollinator species.[6] Its wings feature an easily recognizable black, orange, and white pattern, with a wingspan of 8.9–10.2 cm (​3 1⁄2–4 in)[7] A Müllerian mimic, the viceroy butterfly is similar in color and pattern, but is markedly smaller and has an extra black stripe across each hindwing.

 

The eastern North American monarch population is notable for its annual southward late-summer/autumn migration from the northern and central United States and southern Canada to Florida and Mexico.[4] During the fall migration, monarchs cover thousands of miles, with a corresponding multi-generational return north. The western North American population of monarchs west of the Rocky Mountains often migrates to sites in southern California but has been found in overwintering Mexican sites as well.[8][9] Monarchs have been bred on the International Space Station.[10]

epidemics worldwide [edit]

Commonly and easily mistaken for the similar viceroy butterfly – the two species are Müllerian mimics, the monarch's wingspan ranges from 8.9 to 10.2 centimetres (3.5–4.0 in).[7] The uppersides of the wings are tawny orange, the veins and margins are black, and there are two series of small white spots in the margins. Monarch forewings also have a few orange spots near their tips. Wing undersides are similar, but the tips of forewings and hindwings are yellow brown instead of tawny orange and the white spots are larger.[24] The shape and color of the wings change at the beginning of the migration and appear redder and more elongated than later migrants.[25] Wings size and shape differ between migratory and non-migratory monarchs. Monarchs from eastern North America have larger and more angular forewings than those in the western population.[10]

Monarch flight has been described as "slow and sailing".[26] Monarch flight speed has been estimated by a number of researchers. One scientist examined all prior estimates and concluded their flight speed is approximately 9 km/h or 5.5 mph.[27] For comparison, the average human jogs at a rate of 9.7–12.9 km/h (6–8 mph).

Adults are sexually dimorphic. Males are slightly larger than females[10][24] and have a black patch or spot of androconial scales on each hindwing (in some butterflies, these patches disperse pheromones, but are not known to do so in monarchs). The male's black wing veins are lighter and narrower than those of females.[28]

One variation, the "white monarch", observed in Australia, New Zealand, Indonesia and the United States, is called nivosus by lepidopterists. It is grayish white in all areas of its wings that are normally orange and is only about 1% or less of all monarchs, but populations as high as 10% exist on Oahu in Hawaii.[17]

The monarch has six legs like all insects, but uses only its middle legs and hindlegs as the forelegs are vestigial, as in all Nymphalidae, and held against its body.[29]

conservation efforts [edit]

Many of the priority projects that the national strategy identifies will focus on the I-35 corridor extending for 1,500 miles (2,400 km) from Texas to Minnesota that provides spring and summer breeding habitats in the monarch's key migration corridor.[164]There have been a number of national and local efforts underway to establish pollinator habitat along highways and roadways, although this effort is controversial. Conservationists are lobbying transportation departments and utilities to reduce their use of herbicides and specifically encourage milkweed to grow along roadways and power lines.
 

Reducing roadside mowing and application of herbicides during the butterfly breeding season will encourage milkweed growth.[165] Conservationists lobby agriculture companies to set aside areas that remain unsprayed to allow the butterflies to breed.[132] This practice is controversial because of the high risk of butterfly mortality near roads, as several studies have shown that millions of monarchs and other butterflies are killed by cars every year [139] There is also evidence that monarch larvae living near roads experience physiological stress conditions, as evidenced by elevations in their heart rate.[166]

A 2020 resource from the Cooperative Research Programs of the Transportation Research Board developed products for roadway corridors to provide habitat for monarch butterflies and developed tools for roadside managers to optimize potential habitat for monarch butterflies in their road right-of-ways. [167]

threats [edit]

There is increasing concern related to the ongoing decline of monarchs at their overwintering sites; based on a 2014 twenty-year comparison, the overwintering numbers west of the Rocky Mountains have dropped more than 50 percent since 1997 and the overwintering numbers east of the Rockies have declined by more than 90 percent since 1995.[10]

In February 2015, the U.S. Fish and Wildlife Service provided a statistic showing that nearly a billion monarchs have vanished from the overwintering sites since 1990. At that time, one of the main reasons cited was the herbicides used by farmers and homeowners on milkweed, a plant used as a food source, a home and a nursery by the monarchs.[129] A 2016 study also attributed the last decade's ten-fold decline in overwintering numbers of the eastern monarch population to the loss of breeding habitat, namely the many species of milkweed (Asclepias species) that developing larvae require for food; however, scientists believe there are other factors as well.

 

A number of researchers believe milkweed loss during the breeding season is the cause because declines in milkweed abundance are highly correlated with the adoption of herbicide-tolerant genetically modified corn and soybeans, which now constitute 89% and 94% of these crops, respectively, in the U.S.[122] However, correlative evidence does not prove causation, and other possible causes of the overwintering declines have been proposed. A 2018 study has suggested that the decline in milkweed predates the arrival of GM crops.[130]

taxonomy[edit]

The monarch butterfly or simply monarch (Danaus plexippus) is a milkweed butterfly (subfamily Danainae) in the family Nymphalidae.[4] Other common names depending on region include milkweed, common tiger, wanderer, and black veined brown.[5] It may be the most familiar North American butterfly, and is considered an iconic pollinator species.[6] Its wings feature an easily recognizable black, orange, and white pattern, with a wingspan of 8.9–10.2 cm (​3 1⁄2–4 in)[7] A Müllerian mimic, the viceroy butterfly is similar in color and pattern, but is markedly smaller and has an extra black stripe across each hindwing.

 

The eastern North American monarch population is notable for its annual southward late-summer/autumn migration from the northern and central United States and southern Canada to Florida and Mexico.[4] During the fall migration, monarchs cover thousands of miles, with a corresponding multi-generational return north. The western North American population of monarchs west of the Rocky Mountains often migrates to sites in southern California but has been found in overwintering Mexican sites as well.[8][9] Monarchs have been bred on the International Space Station.[10]

life cycle[edit]

Commonly and easily mistaken for the similar viceroy butterfly – the two species are Müllerian mimics, the monarch's wingspan ranges from 8.9 to 10.2 centimetres (3.5–4.0 in).[7] The uppersides of the wings are tawny orange, the veins and margins are black, and there are two series of small white spots in the margins. Monarch forewings also have a few orange spots near their tips. Wing undersides are similar, but the tips of forewings and hindwings are yellow brown instead of tawny orange and the white spots are larger.[24] The shape and color of the wings change at the beginning of the migration and appear redder and more elongated than later migrants.[25] Wings size and shape differ between migratory and non-migratory monarchs. Monarchs from eastern North America have larger and more angular forewings than those in the western population.[10]

Monarch flight has been described as "slow and sailing".[26] Monarch flight speed has been estimated by a number of researchers. One scientist examined all prior estimates and concluded their flight speed is approximately 9 km/h or 5.5 mph.[27] For comparison, the average human jogs at a rate of 9.7–12.9 km/h (6–8 mph).

Adults are sexually dimorphic. Males are slightly larger than females[10][24] and have a black patch or spot of androconial scales on each hindwing (in some butterflies, these patches disperse pheromones, but are not known to do so in monarchs). The male's black wing veins are lighter and narrower than those of females.[28]

One variation, the "white monarch", observed in Australia, New Zealand, Indonesia and the United States, is called nivosus by lepidopterists. It is grayish white in all areas of its wings that are normally orange and is only about 1% or less of all monarchs, but populations as high as 10% exist on Oahu in Hawaii.[17]

The monarch has six legs like all insects, but uses only its middle legs and hindlegs as the forelegs are vestigial, as in all Nymphalidae, and held against its body.[29]

conservation efforts [edit]

Many of the priority projects that the national strategy identifies will focus on the I-35 corridor extending for 1,500 miles (2,400 km) from Texas to Minnesota that provides spring and summer breeding habitats in the monarch's key migration corridor.[164]There have been a number of national and local efforts underway to establish pollinator habitat along highways and roadways, although this effort is controversial. Conservationists are lobbying transportation departments and utilities to reduce their use of herbicides and specifically encourage milkweed to grow along roadways and power lines.
 

Reducing roadside mowing and application of herbicides during the butterfly breeding season will encourage milkweed growth.[165] Conservationists lobby agriculture companies to set aside areas that remain unsprayed to allow the butterflies to breed.[132] This practice is controversial because of the high risk of butterfly mortality near roads, as several studies have shown that millions of monarchs and other butterflies are killed by cars every year [139] There is also evidence that monarch larvae living near roads experience physiological stress conditions, as evidenced by elevations in their heart rate.[166]

A 2020 resource from the Cooperative Research Programs of the Transportation Research Board developed products for roadway corridors to provide habitat for monarch butterflies and developed tools for roadside managers to optimize potential habitat for monarch butterflies in their road right-of-ways. [167]

threats [edit]

There is increasing concern related to the ongoing decline of monarchs at their overwintering sites; based on a 2014 twenty-year comparison, the overwintering numbers west of the Rocky Mountains have dropped more than 50 percent since 1997 and the overwintering numbers east of the Rockies have declined by more than 90 percent since 1995.[10]

In February 2015, the U.S. Fish and Wildlife Service provided a statistic showing that nearly a billion monarchs have vanished from the overwintering sites since 1990. At that time, one of the main reasons cited was the herbicides used by farmers and homeowners on milkweed, a plant used as a food source, a home and a nursery by the monarchs.[129] A 2016 study also attributed the last decade's ten-fold decline in overwintering numbers of the eastern monarch population to the loss of breeding habitat, namely the many species of milkweed (Asclepias species) that developing larvae require for food; however, scientists believe there are other factors as well.

 

A number of researchers believe milkweed loss during the breeding season is the cause because declines in milkweed abundance are highly correlated with the adoption of herbicide-tolerant genetically modified corn and soybeans, which now constitute 89% and 94% of these crops, respectively, in the U.S.[122] However, correlative evidence does not prove causation, and other possible causes of the overwintering declines have been proposed. A 2018 study has suggested that the decline in milkweed predates the arrival of GM crops.[130]

arrow&v