Heliconius melpomene

Heliconius melpomene, the postman butterfly, common postman or simply postman, is a brightly colored butterfly found throughout Mexico and Central America. It was first described by Carl Linnaeus in his 1758 10th edition of Systema Naturae. Its coloration coevolved with a sister species H. 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 evolutionary radiation of the genus Heliconius and overlapping of its habitat with other related species, H. melpomene has been the subject of extensive study on speciation and hybridization. These hybrids tend to have low fitness as they look different from the original species and no longer exhibit Müllerian mimicry. H. melpomene possesses ultraviolet vision which enhances its ability to distinguish subtle differences between markings on the wings of other butterflies. This allows the butterfly to avoid mating with other species that share the same geographic range. The postman butterfly is predominately black with either red or yellow stripes across the forewings. The postman butterfly has large long wings (35–39 mm). It is poisonous and the red patterns on its wings are an example of aposematism. They look similar to H. 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 parallel evolution between the two species, across morph patterns. 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, although it can also be found near the edges of rivers and streams. It shares its range with other Heliconius species, and H. melpomene is usually less abundant than other species. A recent study, using amplified fragment length polymorphism (AFLP) and mitochondrial DNA datasets, places the origin of H. melpomene to 2.1 million years ago. H. melpomene shows clustering of AFLPs by geography suggesting that the species originated in eastern South America. Caterpillars of Heliconius 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 genus Passiflora 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. Unlike most other butterflies, several Heliconius species have been observed eating pollen as well as nectar. The exact mechanism by which the butterfly digests the pollen is uncertain; it was originally thought that once the pollen was soaked in nectar after ingestion, it would then be able to be digested by the butterfly. Recently, however, the enzyme protease was discovered in the butterfly's saliva, which implies an adaptation for breaking down pollen. This enzyme was found in higher concentrations in the saliva of female butterflies, likely due to the greater need of nutrition associated with reproduction. These adaptations allow the butterflies to extract important amino acids from the pollen, which, in addition to general nutrition benefits, 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 and subsequent enhancement of coloration contributed to the speciation of Heliconius.