Many types of polymorphism can be seen in the

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

Lepidoptera Lepidoptera ( ) is an order (biology), order of insects that includes butterfly, butterflies and moths (both are called lepidopterans). About 180,000 species of the Lepidoptera are described, in 126 Family (biology), families and 46 Taxonomic r ...

. Polymorphism is appearance of forms or "morphs" differing in colour and number of attributes within a single species. In Lepidoptera, polymorphism can be seen not only between individuals in a population, but also between the sexes as ''

sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

'', between geographically separated populations in ''

geographical polymorphism Geography (from Greek: , ''geographia''. Combination of Greek words ‘Geo’ (The Earth) and ‘Graphien’ (to describe), literally "earth description") is a field of science devoted to the study of the lands, features, inhabitants, and ...

'' and also between generations flying at different seasons of the year ('' seasonal polymorphism''). It also includes the phenomenon of

mimicry In evolutionary biology, mimicry is an evolved resemblance between an organism and another object, often an organism of another species. Mimicry may evolve between different species, or between individuals of the same species. Often, mimicry f ...

when mimetic morphs fly alongside non-mimetic morphs in a population of a particular species. Polymorphism occurs both at specific level with heritable variation in the overall morphological design of individuals as well as in certain specific morphological or physiological traits within a species.

Genetic polymorphism

Genetic polymorphism occurs when the morphs are a result of genetic determination only. The extreme case of genetic polymorphism is that of the papilionid great Mormon (''

Papilio memnon ''Papilio memnon'', the great Mormon, is a large butterfly native to southern Asia that belongs to the swallowtail family. It is widely distributed and has thirteen subspecies. The female is polymorphic and with mimetic forms. Range Its range ...

''), where four male forms and many as twenty-six female forms are reported. This species, and others in its genus, have been extensively studied for understanding the genetic basis for polymorphism and

Batesian mimicry Batesian mimicry is a 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. It is named after the English naturalist Henry Walter Bates, after his work on bu ...

. In the case of the scarlet tiger moth ''Callimorpha'' (''Panaxia'') ''dominula'' (family Arctiidae), which is a diurnal moth that occurs in continental Europe, western Asia and southern England, three forms occur in England: the typical homozygote; the rare homozygote (''bimacula'') and the

heterozygote Zygosity (the noun, zygote, is from the Greek "yoked," from "yoke") () is the degree to which both copies of a chromosome or gene have the same genetic sequence. In other words, it is the degree of similarity of the alleles in an organism. Mo ...

(''medionigra''). It was studied there by

E. B. Ford Edmund Brisco "Henry" Ford (23 April 1901 – 2 January 1988) was a British ecological genetics, ecological geneticist. He was a leader among those British biologists who investigated the role of natural selection in nature. As a schoolboy Ford ...

, and later by P. M. Sheppard and their co-workers over many years. Data is available from 1939 to the present day, got by the usual field method of capture-mark-release-recapture and by genetic analysis from breeding in captivity. The records cover gene frequency and population size for much of the twentieth century. In this instance the genetics appears to be simple: two alleles at a single locus, producing the three

phenotypes In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological proper ...

. Total captures over 26 years 1939–1964 came to 15,784 homozygous ''dominula'' (i.e. ''typica''), 1,221 heterozygous ''medionigra'' and 28 homozygous ''bimacula''. Now, assuming equal viability of the genotypes 1,209 heterozygotes would be expected, so the field results do not suggest any heterozygous advantage. It was Sheppard who found that the polymorphism is maintained by selective mating: each genotype preferentially mates with other morphs. This is sufficient to maintain the system despite the fact that in this case the heterozygote has slightly lower viability. Another example is the genetic polyrmorphism of larval developmental rates seen in the ''

Phengaris rebeli ''Phengaris rebeli'' (formerly ''Maculinea rebeli''), common name mountain Alcon blue, is a species of butterfly in the family Lycaenidae. It was first found and described in Styria, Austria, on Mount Hochschwab around 1700. Although it was in ...

'', in which there exist slow-developing larvae (SDL) (75% of the total ''P. rebeli'' larval population) and fast-developing larvae (FDL) (25% of the total ''P. rebeli'' larvae population). The slow-developing larvae do not grow much during the first year, but grow rapidly during the early part of the second summer and remain a second winter within the ant colonies. On the other hand, the FDL complete their growth the following spring after they are taken into the ant nest.

Sexual dimorphism

Sexual dimorphism Sexual dimorphism is the condition where the sexes of the same animal and/or plant species exhibit different morphological characteristics, particularly characteristics not directly involved in reproduction. The condition occurs in most ani ...

is the occurrence of differences between males and females in a species. In Lepidoptera, sexual dimorphism is widespread and almost completely determined by genetic determination. Sexual dimorphism is present in all families of the Papilionoidea and more prominent in the

Lycaenidae Lycaenidae is the second-largest family of butterflies (behind Nymphalidae, brush-footed butterflies), with over 6,000 species worldwide, whose members are also called gossamer-winged butterflies. They constitute about 30% of the known butterfl ...

Pieridae The Pieridae are a large family of butterflies with about 76 genera containing about 1,100 species, mostly from tropical Africa and tropical Asia with some varieties in the more northern regions of North America and Eurasia.DeVries P. J. in Levi ...

and certain taxa of the Nymphalidae. Apart from colour variation which may differ from slight to completely different colour-pattern combinations, secondary sexual characteristics may also be present. Different genotypes maintained by natural selection may also be expressed at the same time. Polymorphic and/or mimetic females occur in the case of some taxa in the

Papilionidae Swallowtail butterflies are large, colorful butterflies in the family Papilionidae, and include over 550 species. Though the majority are tropical, members of the family inhabit every continent except Antarctica. The family includes the larges ...

primarily to obtain a level of protection not available to the male of their species. The most distinct case of sexual dimorphism is that of adult females of many

Psychidae The Psychidae (bagworm moths, also simply bagworms or bagmoths) are a family of the Lepidoptera (butterflies and moths). The bagworm family is fairly small, with about 1,350 species described. Bagworm species are found globally, with some, su ...

species who have only vestigial wings, legs, and mouthparts as compared to the adult males who are strong fliers with well-developed wings and feathery antennae.

Geographical polymorphism

Geographical polymorphism is where geographical isolation causes a divergence of a species into different morphs. A good example is the Indian white admiral (''

Limenitis procris ''Moduza procris'', the commander, sometimes included in the genus ''Limenitis'', is a medium-sized, strikingly coloured brush-footed butterfly found in South Asia and Southeast Asia. It is notable for the mode of concealment employed by its cate ...

'') which has five forms, each geographically separated from the other by large mountain ranges. An even more dramatic showcase of geographical polymorphism is the Apollo butterfly (''Parnassius apollo''). Due to the Apollos living in small local populations, having no contact with each other, but because of the strong stenotopic species and weak migration ability interbreeding between populations of one species practically does not occur; they form over 600 different morphs, with the size of spots on the wings of which varies greatly.

Environmental polymorphism

Environmental polymorphism, where genetic heritability plays no role, is often termed as

polyphenism A polyphenic trait is a trait for which multiple, discrete phenotypes can arise from a single genotype as a result of differing environmental conditions. It is therefore a special case of phenotypic plasticity. There are several types of polyphen ...

. Polyphenism in Lepidoptera is commonly seen in the form of seasonal morphs especially in the butterfly families of Nymphalidae and

. An Old World pierid butterfly, the common grass yellow (''

Eurema hecabe ''Eurema hecabe'', the common grass yellow, is a small pierid butterfly species found in Asia, Africa and Australia. They are found flying close to the ground and are found in open grass and scrub habitats. It is simply known as "the grass yellow ...

'') has a darker summer adult morph, triggered by a long day exceeding 13 hours in duration, while the shorter diurnal period of 12 hours or less induces a paler morph in the post-monsoon period. Polyphenism also occurs in caterpillars, an example being the peppered moth (''Biston betularia'').

Mimicry

Batesian Batesian mimicry is a 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. It is named after the English naturalist Henry Walter Bates, after his work on Bu ...

and Müllerian

complexes are commonly found in Lepidoptera. Genetic polymorphism and natural selection give rise to otherwise edible species (the mimic) gaining a survival advantage by resembling inedible species (the model). Such a mimicry complex is referred to as ''Batesian'' and is most commonly known by the mimicry by the limenitidine viceroy butterfly of the inedible danaine

monarch A monarch is a head of stateWebster's II New College DictionarMonarch Houghton Mifflin. Boston. 2001. p. 707. Life tenure, for life or until abdication, and therefore the head of state of a monarchy. A monarch may exercise the highest authority ...

. Later research has discovered that the viceroy is, in fact more toxic than the monarch and this resemblance should be considered as a case of Müllerian mimicry. In Müllerian mimicry, inedible species, usually within a taxonomic order, find it advantageous to resemble each other so as to reduce the sampling rate by predators who need to learn about the insects' inedibility. Taxa from the toxic genus '' Heliconius'' form one of the most well known Müllerian complexes. The adults of the various species now resemble each other so well that the species cannot be distinguished without close morphological observation and, in some cases, dissection or genetic analysis.

References