Industrial melanism
Industrial melanism is an
Industrial melanism is widespread in the
Other explanations for the observed correlation with industrial pollution have been proposed, including strengthening the immune system in a polluted environment, absorbing heat more rapidly when sunlight is reduced by air pollution, and the ability to excrete trace elements into melanic scales and feathers.
History
Industrial melanism was first noticed in 1900 by the geneticist William Bateson; he observed that the colour morphs were inherited, but did not suggest an explanation for the polymorphism.[1][6]
In 1906, the geneticist Leonard Doncaster described the increase in frequency of the melanic forms of several moth species from about 1800 to 1850 in the heavily industrialised north-west region of England.[7]
In 1924, the evolutionary biologist J. B. S. Haldane constructed a mathematical argument showing that the rapid growth in frequency of the carbonaria form of the peppered moth, Biston betularia, implied selective pressure.[8][9]
From 1955 onwards, the geneticist
By 1973, pollution in England had begun to decrease, and the dark carbonaria form had declined in frequency. This provided convincing evidence, gathered and analysed by Kettlewell and others such as the entomologist and geneticist Michael Majerus and the population geneticist Laurence M. Cook, that its rise and fall had been caused by natural selection in response to the changing pollution of the landscape.[14][15][16]
Taxonomic range
Industrial melanism is known from over 70 species of moth that Kettlewell found in England, and many others from Europe and North America.[17] Among these, Apamea crenata (clouded border brindle moth) and Acronicta rumicis (knot grass moth) are always polymorphic, though the melanic forms are more common in cities and (like those of the peppered moth) are declining in frequency as those cities become less polluted.[1]
Among other insects, industrial melanism has been observed in a beetle (Adalia bipunctata, the two-spot ladybird[18]) and a barklouse (Mesopsocus unipunctatus[19]).
In the vertebrates, industrial melanism is known from the turtle-headed seasnake Emydocephalus annulatus,[20] and may be present in urban feral pigeons.[21]
Camouflage
Originally, peppered moths lived where light-colored
Melanic B. betularia have been widely observed in North America. In 1959, 90% of B. betularia in
An additional study in 2018 further quantified survivability by looking at color and luminance camouflage and avian artificial predation models. For color camouflage, typica moths blended better under lichen bark than carbonaria, but when placed under plain bark, there was no significant difference. However, in luminance camouflage, carbonaria moths blended better compared to typica on a plain bark tree. When both variants were placed on an unpolluted lichen covered tree, typica moths had a 21% better survival rate.[28]
Controversy
Kettlewell's experiments were criticised by the zoologist Theodore David Sargent, who failed to reproduce Kettlewell's results between 1965 and 1969, and argued that Kettlewell had specially trained his birds to give the desired results.[29][30][31][32] Michael Majerus however found that Kettlewell was basically correct in concluding that differential bird predation in a polluted environment was the primary cause of industrial melanism in the peppered moth.[33] The story was in turn taken up in a 2002 book Of Moths and Men, by the journalist Judith Hooper, asserting that Kettlewell's findings were fraudulent.[34] The story was picked up by creationists who repeated the assertions of fraudulence.[35] Zoologists including L. M. Cook, B. S. Grant, Majerus and David Rudge however all upheld Kettlewell's account, finding that each of Hooper's and the creationists' claims collapsed when the facts were examined.[3][33][36][37][38][39]
It has been suggested that the demonstrated relationship between melanism and pollution can not be fully proven because the exact reason for increase in survivability can not be tracked and pin-pointed. However, as air quality has improved in industrial areas of America and Britain, through improved
Alternative explanations
Immunity
In 1921, the evolutionary biologist
Nearly a century later, it was suggested that the moth's industrial melanism might, in addition (
Trace metal excretion
A non-camouflage mechanism has been suggested for some vertebrates. In tropical ocean regions subject to industrial pollution the turtle-headed seasnake Emydocephalus annulatus is more likely to be melanic. These snakes shed their skin every two to six weeks. Sloughed skin contains toxic minerals, higher for dark skin, so industrial melanism could be selected for through improved excretion of trace elements.[a][20] The same may apply in the case of urban feral pigeons, which have the ability to remove trace metals such as zinc to their feathers. However, toxic lead was not found to accumulate in feathers, so the putative mechanism is limited in its range.[21]
Thermal advantage
Melanic forms of the two-spot ladybird
However, thermal melanism failed to explain the distribution of the species near Helsinki where the city forms a relatively warm 'heat island', while near the Finnish coast there is more sunlight as well as more melanism, so the selective pressure driving melanism requires a different explanation.[44] A study in Birmingham similarly found no evidence of thermal melanism but a strong correlation with smoke pollution; melanism declined from 1960 to 1978 as the city became cleaner. Further, the same study found that a related species, Adalia decempunctata, experienced no change in frequency of melanism in the same places in that period.[45]
Notes
References
- ^ PMID 18941471.
- .
- ^ S2CID 25525719.
- ^ .
- ^ .
- ^ Bateson, William (1900). "Collective enquiry as to progressive melanism in moths—memorandum from the Evolution Committee of the Royal Society". Entomological Record. 12: 140.
- ^ Doncaster, Leonard (1906). "Collective enquiry as to progressive melanism in Lepidoptera". Entomological Record. 18: 165–168, 206–208, 222–276.
- PMID 2185859. Originally published in Trans Camb Phil Soc 23: 19–41.
- ^ Haldane, J. B. S. (1932). The Causes of Evolution. Longmans.
- .
- S2CID 81591392.
- .
- .
- ISBN 978-0198573708.
- ISBN 978-0198549826.
- S2CID 26831926.
- ISBN 978-94-010-0585-2., which cites Kettlewell 1973.
- ^ JSTOR 2402167.
- ^ Popescu, C. (1979). "Natural selection in the industrial melanic psocid Mesopsocus unipunctatus (Müll.) (Insecta: Psocoptera) in northern England". Heredity (42): 133–142.
- ^ PMID 28803870.
- ^ PMID 24671830.
- .
- S2CID 85594029.
- PMID 23211788.
- .
- PMID 12140267.
- PMID 11075707.
- PMID 30271998.
- S2CID 32124765.
- S2CID 4202131.
- ISBN 978-1-4381-1005-9.
- ISBN 978-0306429774.
- ^ ISBN 978-0198549833.
- ISBN 978-0-393-32525-6.
- ^ Frack, Donald (16 April 1999). "Evolution — April 1999: Peppered Moths and Creationists". Archived from the original on 26 August 2007. Retrieved 2007-08-26.
- S2CID 26831926.
- S2CID 161367302.
- ISBN 978-1-84593-140-7.
- PMID 16549216.
- .
- ISBN 978-3-0348-5855-7.
- PMID 9017902.
- .
- JSTOR 23734522.
- hdl:1887/11037.