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The Heliconius butterflies are the most speciose genus within the Heliconiini, displaying a dramatic diversity of colour patterns at species and sub-species level. They are also famous for Müllerian mimicry, with many species converging on a common wing pattern where they live together. Heliconius communities commonly consist of several ‘mimicry rings’, groups of species that share a common pattern.
Colour pattern diversity of H. numata (top two rows), and H. melpomene (third row) with its co-mimic H.erato (bottom row).
Heliconius butterflies have two unique, derived ecological traits that may have facilitated rapid adaptive radiation: pollen feeding and pupal-mating behaviour (Gilbert, 1972). Adult butterflies systematically collect pollen from flowers, which they masticate on the proboscis to dissolve out amino acids. This allows caterpillars to develop relatively rapidly (since they do not need to store nutrients for egg and sperm production), and allows adults to have a greatly extended lifespan – up to 8 months – in the wild.
Heliconius butterflies with proboscis bearing pollen collected from flowers. The diets of most Lepidoptera are very limited in nitrogenous compounds, and pollen feeding is thought to increase longevity and egg production in Heliconius butterflies. Images © Mathieu Joron
The pollen-feeding behaviour centres around a group of vines in the Cucurbitaceae, Psiguria and Gurania. This is a tight plant-pollinator relationship in which the butterflies are major pollinators for the plants and the plants major food resources for adult maintenance and egg production. 80% of a female's egg production come from amino acids that come from pollen she collects. Only 20% comes from amino acids acquired by the caterpillars feeding on passion vines. In most butterflies and moths, 100% of eggs derive from the efforts of the larval stage, and eggs are laid in a quick pulse after adult emergence. In Heliconius, eggs are laid as they are manufactured over the adult's long lifespan (Gilbert, 1972). The butterflies learn the locations of pollen plants and establish home ranges based on pollen foraging routes. It appears that the pollen plants are more significant than larval hosts in determining a female's assessment of the habitat. Thus, as long as she knows the locations of a network of pollen plants, she will stay in the area, even during periods when new shoots of passion vine hosts are temporarily not available due to weather or defoliation by Heliconius or other competing herbivores. So while most herbivorous insects disperse away when suitable oviposition sites are scarce, Heliconius females are content to stay put as long as the mutualist plant produces pollen (which is year-round). Moreover the pollen promotes a long reproductive life so that females can wait many weeks for the opportunity to resume egg-laying (Ehrlich & Gilbert, 1973).
Heliconius sapho male sitting on a female pupa. Mating takes place as the female begins to eclose, and females mate only once. © Jamie Walters
A second unusual trait found in some Heliconius species is a unique mating behaviour known as pupal-mating. Males of certain species search larval food plants for female pupae. The males then sit on the pupae a day before emergence, and mating occurs the next morning, before the female has completely eclosed (Gilbert, 1976; Deinert et al. 1994). Various kinds of pupal-mating occur scattered across several insect orders (Thornhill & Alcock, 1993); in passion-vine butterflies almost half the Heliconius species (42%) are pupal-maters (Gilbert, 1991, pupal mating clade marked in the cladogram above).
Gilbert (1991) suggested that pupal-mating might play an important role in the radiation of Heliconius as well as in the packing of Heliconius species into local habitats. Pupal-mating might enhance the possibility of intrageneric mimicry because in many cases, mimetic species pairs consist of a pupal-mating and a non pupal-mating species. The strikingly different mating tactics of these groups could allow phenotypically identical species to occupy the same habitats without mate recognition errors. Second, this mating tactic may influence host-plant specialisation, as it has been suggested that pupal-mating species may displace other heliconiines from their hosts by interference competition (Gilbert, 1991). Males of these species sit on, attempt to mate with, and disrupt eclosion of other Heliconius species of both mating types encountered on the host plant. This aggressive behaviour may prevent other heliconiine species from evolving preference for host plants used by pupal-mating species.
Etymology: Heliconius signifies dwellers on Mount Helicon (Turner, 1976) (see each species for more information). Helicon is a mountain in southern Greece, in Boeotia, regarded in ancient Greece, as the source of poetry and inspiration. From it flowed the fountains of Aganippe and Hippocrene, associated with Muses. The nine Muses are daughters of Zeus and Mnemosyne, the goddess of memory. The Muses sat near the throne of Zeus, king of the gods, and sang of his greatness and of the origin of the world and its inhabitants and the glorious deeds of the great heroes. From their name words such as music, museum, mosaic are derived (Muses). The nine muses are:
- Calliope Epic and heroic poetry and the head muse
- Clio History
- Erato Love-poetry
- Euterpe Music and Lyric poetry
- Melpomene Tragedy
- Polyhymnia Sublime hymns or serious sacred songs
- Terpsichore Dancing and choral song
- Thalia Comedy and idyllic poetry
- Urania Astronomy
- Stalachtis calliope (L.), 1758 (Riodinidae)
- Eresia clio (L.), 1758 (Nymphalinae)
- Heliconius erato (L.), 1758
- Stalachtis euterpe (L.), 1758 (Riodinidae)
- Heliconius melpomene (L.), 1758
- Mechanitis polymnia (L.), 1758 (Ithomiini) (a variant spelling of Polyhymnia)
- Acraea terpsichore (L.), 1758 (Acraeini, African)
- Actinote thalia (L.), 1758 (Acraeini)
- Taenaris urania (L.), 1758 (Amathusiini, Australasian)