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Heliconius melpomene, the postman butterfly, common postman or simply postman, is a brightly colored butterfly found throughout Mexico and Central America. Its coloration co-evolved with a sister species Heliconius erato as a warning to predators of its inedibility; this is an example of Müllerian mimicry. H. melpomene was one of the first butterfly species observed to forage for pollen, a behavior that is common in other groups but rare in butterflies. Because of the recent rapid radiation of the Heliconius genus, H. melpomene has been the subject of extensive study on speciation and hybridization. The species possesses adaptations such as UV light vision that enhance its ability to distinguish between subtle markings on the wings of other butterflies. This counteracts the fact that its range overlaps with its sister species and prevents heterospecific mating.

Description
The postman butterfly has large long wings with an orange stripe down each forewing. It is poisonous and has red patterns on its wings. They tend to look similar to the species Heliconius erato. Two features found on the underside help to distinguish H. erato from H. melpomene—H. erato has four red dots where the wing attaches to the thorax while H. melpomene has three and the yellowish white stripe on the underside reaches the margin of the hindwing in H. erato but ends before reaching the margin in H. melpomene.

There are many morphs of this butterfly throughout Central and South America. The geographical variation in patterns has been studied using linkage mapping and it has been found that the patterns are associated with a small number of genetic loci called genomic "hotspots". Hotspot loci for color patterning have been found homologous between co-mimics H. erato and H. melpomene, strengthening evidence for the parallel evolution between the two species, across morph patterns.

Geographic Range and Habitat
H. melpomene is found from Mexico to South America, especially on the slopes of the Andes mountains. It most commonly inhabits open terrain and forest edges.

Origins
A recent study, using amplified fragment length polymorphism (AFLP) and mitochondrial DNA (mtDNA) datasets, places the origins of H. melpomene at 2.1 Mya. H. melpomene shows clustering of AFLPs by geography suggesting that the species originated in eastern South America.

Caterpillars
Caterpillars of Heilconius exhibit a behavior known as monophagy, meaning they feed on only one kind of plant, specifically the genus Passiflora. In H. melpomene, the host plants are limited to Passiflora oerstedii and Passiflora menispermifolia. Species of the Passiflora genus have evolved many chemical defenses, but Heliconius caterpillars have developed adaptations that allow them to continue to feed on the plants and actually incorporate the toxic compounds into their systems and make them unpalatable to predators. These interactions make Heliconius and Passiflora a model system for studies of coevolution.

Diet
Unlike most other butterflies, several Heliconius species have been observed eating pollen as well as nectar. When foraging, the butterfly extracts amino acids from the pollen by dissolving it in nectar. This additional nutrition allows H. melpomene to have brighter colors and be more distasteful to predators than their non-pollen foraging counterparts. It is thought that this foraging adaptation contributed to the speciation of Heliconius.

Pollination
While foraging, adults accumulate pollen on the end of their proboscis and the grains stay there for long periods of time. While there are many plants in H. melpomene’s range that are chemically suitable, only a few of these are visited by the butterfly. This makes the butterfly an efficient pollinator for the flowers it visits.

Parental Care
By foraging for pollen while developing eggs, female H. melpomene provide valuable amino acids and proteins to their offspring. This reduces the amount of time that the offspring must spend foraging during the larval stage, and thus decreases the chances of larval predation. While this extra foraging behavior on the part of the female increases her likelihood of being eaten, the warning colors highlighting her distaste protect her from would be predators.

Oviposition
Female H. melpomene butterflies recognize host plants by identifying the corresponding chemical compound using taste receptors located on the forelegs. When searching for a plant, the butterfly will drum her legs on the plant in order to detect the chemical compounds the plant releases. Once she has found her correct host plant, she will lay her eggs on the young leaves.

Mimicry
H. melpomene co-evolved with a sister species, Heliconius erato, each developing similar bright color patterns. This coloration warns potential predators that the butterflies are distasteful and should be avoided. Since both species possess this acrid taste, they display what is known as Müllerian mimicry. Despite their easily confused coloration, these two species are able to exist in the same habitat range because they are reproductively isolated.

Chemical Defense
Both males and females release a strong odor detectable even to humans when handled in order to deter predation. Additionally, H. melpomene butterflies render themselves toxic by producing cyanogenic glycosides in both the larval and adult stages.

Subspecies
Subspecies of Heliconius melpomene include:
 * H. m. aglaope (C. & R. Felder, 1862)
 * H. m. amandus (Grose-Smith & Kirby, 1892)
 * H. m. amaryllis (C. & R. Felder, 1862)
 * H. m. cythera (Hewitson, 1869)
 * H. m. euryades (Riffarth, 1900)
 * H. m. malleti (Lamas, 1988)
 * H. m. melpomene (Linnaeus, 1758)
 * H. m. meriana (Turner, 1967)
 * H. m. modesta (Riffarth, 1900)
 * H. m. nanna (Stichel, 1899)
 * H. m. penelope (Staudinger, 1894)
 * H. m. plesseni (Riffarth, 1907)
 * H. m. sticheli (Riffarth, 1907)
 * H. m. rosina (Boisduval, 1870)
 * H. m. thelxiope (Hübner, [1806])
 * H. m. unimaculata (Hewitson, 1869)
 * H. m. vicinus (Ménétriés, 1847)
 * H. m. vulcanus (Butler, 1865)
 * H. m. xenoclea (Hewitson, [1853]

Hybridization
Due to its overlapping range with many closely related species, H. melpomene often hybridizes in nature. Females resulting from the cross of H. melpomene and Heliconius cydno are sterile. While hybrid males are not sterile, they exhibit patterns that are intermediate to the crossed species and thus the males are not likely to be recognized as mates by either species. Furthermore, the patterns on both sexes will be non-mimetic, meaning they will not be recognized by predators as displays of distaste. Therefore the hybrids resulting from the cross of H. melpomene with other Heliconius species have low fitness and are not likely to persist.

Mate Searching
When searching for mates, males of H. melpomene exhibit patrolling behavior, which involves searching for potential mates while flying around the area. This requires the ability to distinguish H. melpomene females from those of other species.

Female/Male Interactions
Male H. melpomene possess abdominal claspers that are used to grasp females for forced copulations. During mating, the male passes nutrients in a spermatophore; the female can use this nuptial gift to nourish the fertilizing eggs inside her. In addition to the spermatophore, males also deliver a pheromone to the female that serves as an anti-aphrodisiac. This compound produces an odor that deters other potential mates, thus increasing the likelihood of the male’s reproductive success. The pheromone is produced only in males and is secreted to identify themselves to other males, so the anti-aphrodisiac works by making the female smell like a male.

Vision
Due to a duplication in a gene for UV light detection, H. melpomene individuals are capable of distinguishing between a wider range of yellow shades than other butterfly species. Additionally, when looking for mates, the butterflies distinguish conspecifics from hybrids and heterospecifics by detecting subtle changes in marking patterns on wings. These adaptations allow the butterflies to avoid genetically costly mates, as hybrid females are sterile and hybrid males in this system are less fit due to disruptive sexual selection.

Gustatory
While both sexes of H. melpomene possess taste receptors on their back legs, only the female butterflies have the receptors on the forelegs; this is an example of sexual dimorphism. The taste receptors are used by both species in order to find food and mates, but the female must also use the sense to find suitable host plants for her eggs.