A report on Polymorphism (biology)

The white morph of the monarch in Hawaii is partly a result of apostatic selection.

Occurrence of two or more clearly different morphs or forms, also referred to as alternative phenotypes, in the population of a species.

- Polymorphism (biology)
The white morph of the monarch in Hawaii is partly a result of apostatic selection.

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A red tulip exhibiting a partially yellow petal due to a mutation in its genes

Mutation

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Alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA.

Alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA.

A red tulip exhibiting a partially yellow petal due to a mutation in its genes
Mutation with double bloom in the Langheck Nature Reserve near Nittel, Germany
Prodryas persephone, a Late Eocene butterfly
A covalent adduct between the metabolite of benzo[a]pyrene, the major mutagen in tobacco smoke, and DNA
Five types of chromosomal mutations
Selection of disease-causing mutations, in a standard table of the genetic code of amino acids
The structure of a eukaryotic protein-coding gene. A mutation in the protein coding region (red) can result in a change in the amino acid sequence. Mutations in other areas of the gene can have diverse effects. Changes within regulatory sequences (yellow and blue) can effect transcriptional and translational regulation of gene expression.
The distribution of fitness effects (DFE) of mutations in vesicular stomatitis virus. In this experiment, random mutations were introduced into the virus by site-directed mutagenesis, and the fitness of each mutant was compared with the ancestral type. A fitness of zero, less than one, one, more than one, respectively, indicates that mutations are lethal, deleterious, neutral, and advantageous.
A mutation has caused this moss rose plant to produce flowers of different colors. This is a somatic mutation that may also be passed on in the germline.
Dutch botanist Hugo de Vries making a painting of an evening primrose, the plant which had apparently produced new forms by large mutations in his experiments, by Thérèse Schwartze, 1918

A 2007 study on genetic variations between different species of Drosophila suggested that, if a mutation changes a protein produced by a gene, the result is likely to be harmful, with an estimated 70% of amino acid polymorphisms that have damaging effects, and the remainder being either neutral or marginally beneficial.

E. B. Ford

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British ecological geneticist.

British ecological geneticist.

Callimorpha dominula morpha typica with spread wings. Polymorphism in this species was investigated by Ford for many years. The red with black rear wings, revealed in flight, warn of its noxious taste. The front wings are cryptic, covering the rear wings at rest. Here the moth, on a human hand, is resting but alert, and has jinked the front wings forward to reveal the warning flash.

E.B. Ford worked for many years on genetic polymorphism.

The shells of individuals within the bivalve mollusk species Donax variabilis show diverse coloration and  patterning in their phenotypes.

Phenotype

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Set of observable characteristics or traits of an organism.

Set of observable characteristics or traits of an organism.

The shells of individuals within the bivalve mollusk species Donax variabilis show diverse coloration and  patterning in their phenotypes.
Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of petal color in pea plants. The letters B and b represent genes for color, and the pictures show the resultant phenotypes. This shows how multiple genotypes (BB and Bb) may yield the same phenotype (purple petals).
ABO blood groups determined through a Punnett square and displaying phenotypes and genotypes
Biston betularia morpha typica, the standard light-colored peppered moth
B.betularia morpha carbonaria, the melanic form, illustrating discontinuous variation

When two or more clearly different phenotypes exist in the same population of a species, the species is called polymorphic.

Fisher in 1913

Ronald Fisher

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British polymath who was active as a mathematician, statistician, biologist, geneticist, and academic.

British polymath who was active as a mathematician, statistician, biologist, geneticist, and academic.

Fisher in 1913
Fisher in 1913
As a child
Inverforth House, North End Way NW3, where Fisher lived from 1896 to 1904
On graduating from Cambridge University, 1912
The peacock tail in flight, the classic example of a Fisherian runaway
Rothamsted Research
Memorial plaque over his remains, lectern-side aisle of St Peter's Cathedral, Adelaide
Stained glass window (now removed) in the dining hall of Caius College, in Cambridge, commemorating Ronald Fisher and representing a Latin square, discussed by him in The Design of Experiments
As a steward at the First International Eugenics Conference, 1912

In ecological genetics he and E. B. Ford showed that the force of natural selection was much stronger than had been assumed, with many ecogenetic situations (such as polymorphism) being maintained by the force of selection.

Biston betularia caterpillars on birch (left) and willow (right), demonstrating a color polyphenism.

Polyphenism

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Trait for which multiple, discrete phenotypes can arise from a single genotype as a result of differing environmental conditions.

Trait for which multiple, discrete phenotypes can arise from a single genotype as a result of differing environmental conditions.

Biston betularia caterpillars on birch (left) and willow (right), demonstrating a color polyphenism.
Insect castes: Replete and worker honeypot ants Myrmecocystus mimicus
Third stage dauer larva (resting stage) of Phasmarhabditis hermaphrodita

When polyphenic forms exist at the same time in the same panmictic (interbreeding) population they can be compared to genetic polymorphism.

Anvil stone, where a thrush has broken open the shells of polymorphic grove snails, may be a sign of frequency-dependent selection.

Frequency-dependent selection

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Evolutionary process by which the fitness of a phenotype or genotype depends on the phenotype or genotype composition of a given population.

Evolutionary process by which the fitness of a phenotype or genotype depends on the phenotype or genotype composition of a given population.

Anvil stone, where a thrush has broken open the shells of polymorphic grove snails, may be a sign of frequency-dependent selection.
Müllerian mimetic species of Heliconius from South America
Venomous coral snake's warning coloration can benefit harmless mimics, depending on their relative frequency.
Harmless scarlet kingsnake mimics the coral snake, but its pattern varies less where the coral snake is rare.

Frequency-dependent selection can lead to polymorphic equilibria, which result from interactions among genotypes within species, in the same way that multi-species equilibria require interactions between species in competition (e.g. where αij parameters in Lotka-Volterra competition equations are non-zero).

Ecological genetics

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Study of genetics in natural populations.

Study of genetics in natural populations.

Examples might be: flowering time, drought tolerance, polymorphism, mimicry, and avoidance of attacks by predators.

Plate from Bates 1861, illustrating Batesian mimicry between Dismorphia species (top row and third row) and various Ithomiini (Nymphalidae) (second and bottom rows). A non-Batesian species, Pseudopieris nehemia, is in the centre.

Batesian mimicry

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Form of mimicry where a harmless species has evolved to imitate the warning signals of a harmful species directed at a predator of them both.

Form of mimicry where a harmless species has evolved to imitate the warning signals of a harmful species directed at a predator of them both.

Plate from Bates 1861, illustrating Batesian mimicry between Dismorphia species (top row and third row) and various Ithomiini (Nymphalidae) (second and bottom rows). A non-Batesian species, Pseudopieris nehemia, is in the centre.
Henry Walter Bates described the form of mimicry that bears his name in 1861.
The yellow-banded poison dart frog (Dendrobates leucomelas) has conspicuous aposematic coloration.
The hoverfly Spilomyia longicornis is an imperfect Batesian mimic of wasps, lacking their long antennae and wasp waist.
Tiger moths like Cycnia tenera are aposematic by sound, emitting ultrasonic warning signals. They are mimicked by pyralid moths, which are not foul-tasting but emit similar sounds.

Some mimetic populations have evolved multiple forms (polymorphism), enabling them to mimic several different models and thereby to gain greater protection.

Plate from Henry Walter Bates (1862) illustrating Batesian mimicry between Dismorphia species (top row, third row) and various Ithomiini (Nymphalidae, second row, bottom row)

Mimicry

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Evolved resemblance between an organism and another object, often an organism of another species.

Evolved resemblance between an organism and another object, often an organism of another species.

Plate from Henry Walter Bates (1862) illustrating Batesian mimicry between Dismorphia species (top row, third row) and various Ithomiini (Nymphalidae, second row, bottom row)
Mimesis in Ctenomorphodes chronus, camouflaged as a eucalyptus twig
Macroxiphus sp katydid mimics an ant
Common hawk-cuckoo resembles a predator, the shikra.
Many insects including hoverflies and the wasp beetle are Batesian mimics of stinging wasps.
The Heliconius butterflies from the tropics of the Western Hemisphere are the classical model for Müllerian mimicry.
Comparison of Batesian and Müllerian mimicry, illustrated with a hoverfly, a wasp and a bee
The deadly Texas coral snake, Micrurus tener (the Emsleyan/Mertensian mimic)
The harmless Mexican milk snake, Lampropeltis triangulum annulata (the Batesian mimic)
Rye is a secondary crop, originally being a mimetic weed of wheat.
Monarch caterpillars, shown feeding, vary in toxicity depending on their diet.
The spotted predatory katydid (Chlorobalius leucoviridis), an acoustic aggressive mimic of cicadas
Two bluestreak cleaner wrasse cleaning a potato grouper, Epinephelus tukula
Mimicry in a brood parasite: Cuckoo adult mimics sparrowhawk, alarming small birds enough to give female cuckoo time to lay eggs in their nests.
Egg mimicry: cuckoo eggs (larger) mimic many species of host birds' eggs, in this case of reed warbler.
The fly orchid (Ophrys insectifera)
Eyespots of foureye butterflyfish (Chaetodon capistratus) mimic its own eyes, deflecting attacks from the vulnerable head.
Pygmy owl (Glaucidium californicum) showing eyespots on back of head
Larva of elephant hawkmoth (Deilephila elpenor, Sphingidae), displaying eye-spots when alarmed
Automimicry: many blue butterflies (Lycaenidae) such as this gray hairstreak (Strymon melinus) have a false head at the rear, held upwards at rest.

Mimics may have different models for different life cycle stages, or they may be polymorphic, with different individuals imitating different models, such as in Heliconius butterflies.

Lucretius

Evolution

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Change in the heritable characteristics of biological populations over successive generations.

Change in the heritable characteristics of biological populations over successive generations.

Lucretius
Alfred Russel Wallace
Thomas Robert Malthus
In 1842, Charles Darwin penned his first sketch of On the Origin of Species.
DNA structure. Bases are in the centre, surrounded by phosphate–sugar chains in a double helix.
Duplication of part of a chromosome
This diagram illustrates the twofold cost of sex. If each individual were to contribute to the same number of offspring (two), (a) the sexual population remains the same size each generation, where the (b) Asexual reproduction population doubles in size each generation.
Mutation followed by natural selection results in a population with darker colouration.
Simulation of genetic drift of 20 unlinked alleles in populations of 10 (top) and 100 (bottom). Drift to fixation is more rapid in the smaller population.
Homologous bones in the limbs of tetrapods. The bones of these animals have the same basic structure, but have been adapted for specific uses.
A baleen whale skeleton. Letters a and b label flipper bones, which were adapted from front leg bones, while c indicates vestigial leg bones, both suggesting an adaptation from land to sea.
Common garter snake (Thamnophis sirtalis sirtalis) has evolved resistance to the defensive substance tetrodotoxin in its amphibian prey.
The four geographic modes of speciation
Geographical isolation of finches on the Galápagos Islands produced over a dozen new species.
Tyrannosaurus rex. Non-avian dinosaurs died out in the Cretaceous–Paleogene extinction event at the end of the Cretaceous period.
The hominoids are descendants of a common ancestor.
As evolution became widely accepted in the 1870s, caricatures of Charles Darwin with an ape or monkey body symbolised evolution.

Generally, sympatric speciation in animals requires the evolution of both genetic differences and nonrandom mating, to allow reproductive isolation to evolve.