Polygonia c-album, or the comma, is a food generalist (polyphagous) butterfly species belonging to the family Nymphalidae. The angular notches on the edges of the forewings are characteristic of the genus Polygonia, which is why species in the genus are commonly referred to as anglewing butterflies. Comma butterflies can be identified by their prominent orange and dark brown/black dorsal wings.
Both the larval and adult stages exhibit protective camouflage, mimicking bird droppings and fallen leaves respectively, which reduces predation. The pupae are also cryptic, resembling shriveled leaves. During the later stage of development, the larvae also develop strong spines along their backs. The species is commonly found in Europe, North Africa, and Asia, and contains several subspecies. Although the species is not migratory, the butterflies are strong fliers, resulting in an open population structure with high gene flow and increased genetic variation.
Description
thumb|200px|Dorsal view of Polygonia c-album in [[Salary Brook Local Nature Reserve, Colchester, Essex, July 2024.]]
The outer margins of the wings are strongly and irregularly dentate, excavated and angulated.
The upper side of the wings has a bright orange color, decorated with brown marks and light spots on the edge. The reverse is marbled with brown. Folded, the butterfly looks like a dead leaf. The hindwings have on the reverse side a white spot usually in the shape of a comma.
The sexual dimorphism is slight and concerns the intensity of the coloration, the silhouette and the size, the male having a wingspan of 22 to 24 mm. and the female of 25 to 26 mm. The seasonal dimorphism is more marked: the first generation ( hutchinsoni form, named for Emma Hutchinson, May-June) has the upperside fawn orange and the underside brown-gold and the hindwing bears distally a broad dark red-brown area in which is situated a row of light brown hastate spots. The underside is dark, being either unicolorous or prominently marmorated, while the second generation (form c-album (July, in autumn and spring after overwintering) has a more red upper and dark brown underside (ground-colour is less bright). In the summer form the wings are less dentate, and the hindwing has a narrow dark submarginal band, near which stands a row of light lunules proximally bordered by a band of brown arcs. The underside is of a paler color, being less distinctly — sometimes, however, very prominently — marmorated and shaded.
Taxonomy and phylogeny
The comma belongs to the family Nymphalidae, the largest family of butterflies with 13 subfamilies. Within the genus Polygonia, a sister-group relationship between P. c-album and P. faunus is strongly supported by larval development analysis and synapomorphies. In both species, the adults and larvae have similar polyphagous habits. The genus Polygonia is also closely related to the genera Kanisha and Roddia, each containing a single species: K. canace and R. l-album.
Geographic range and habitat
The comma inhabits areas including Europe, North Africa, and Asia. It is primarily a woodland butterfly, living in low-density forests with sunshine and moist soil. Specifically, the species is commonly found in the woodland, country lanes, and garden areas of Norway, Sweden, and Great Britain.
Subspecies
thumb |Form hutchinsoni (named for [[Emma Hutchinson) Northamptonshire, UK]]
The following subspecies are found in the indicated parts of the comma's range:
- P. c. c-album Europe
- P. c. imperfecta <small>(Blachier, 1908)</small> North Africa
- P. c. extensa <small>(Leech, 1892)</small> western China, central China
- P. c. kultukensis <small>(Kleinschmidt, 1929)</small> Transbaikalia
- P. c. hamigera <small>(Butler, 1877)</small> Ussuri (type locality Edo, Japan)
- P. c. koreana <small>(Bryk, 1946)</small> Korea
- P. c. sachalinensis <small>(Matsumura, 1915)</small> Sakhalin
- P. c. asakurai <small>(Nakahara, 1920)</small> Taiwan
- P. c. agnicula <small>(Moore, 1872)</small> Nepal
Food resources
Larval host plant preferences and selection
For comma butterflies, food resources consumed during development are the primary source of nitrogen and protein during adulthood. Because they feed exclusively on plants, making them a phytophagous species, the quality of plants upon which the larvae feed is strongly correlated with their future fitness. The larval form is often divided into five developmental stages known as instars. Although during the first three instars larvae are observed to remain almost entirely upon the underside of leaves, the fourth and fifth instar larvae are more active in obtaining food resources. The later instar larvae are specialized feeders and favor several host plants during the larval stage: Urtica dioica, Ulmus glabra, Salix caprea, R. uva-crispa, and Betula pubescens. While pupal weight and overall larval survival rates are similar among larvae regardless of host plant, the larval development times differ significantly. As a result, larvae prefer feeding on plants that allow them to develop in the shortest amount of time. Larvae reared on U. dioica demand the shortest development time and is thus favored over other plants. On the other hand, B. pubescens is at the bottom of the host plant preference hierarchy.
<gallery mode="packed">
File:Nettle - Ortica - Foto Giovanni Dall'Orto.jpg |Urtica dioica
File:Ulmus glabra - 1.jpg |Ulmus glabra
File:Salix caprea.jpg |Salix caprea
</gallery>
Reproduction and life history
Mating
Mating system
Comma butterflies have a polyandrous mating system where females mate with multiple males to receive the necessary amount of sperm to fertilize their eggs.
Female mate choice
Females exercise mate choice before, during, and after mating and can distinguish between males who were reared on high-quality versus low-quality host plants. The ability to recognize adults reared on higher quality host plants is selected for because males fed better plants during development provide superior nuptial gifts. In comma butterflies, nuptial gifts are edible spermatophores containing spermatozoa and nutrients. When comparing the two common host plants U. dioica and S. caprea, females preferentially choose to mate with males reared on U. dioica, because these males have higher protein content and increased spermatophore production. This pattern of deviation results from the open population structure with high gene flow.
Parent-offspring conflict
In theory, females would prefer host plants where their offspring performance is maximized, and the larvae would benefit from being able to feed on the best resources nearby their hatch site. However, this is not always observed in nature due to external factors such as predators, parasites, and pathogens. Instead, there is a trade-off between female host plant preference and larval fitness in many species of butterfly. In P. c-album, instead of accepting the host plant that the female selected, first instar larvae leave their hatch site in search of alternative food sources. After each egg is laid, the female scouts out other possible host plants before determining the site of her next egg. which generally takes four to five days. Although the female can allocate more resources into egg production based on the nuptial gifts received by mates, the total number of eggs laid or the mass of the eggs are altered based on the host plant. A lack of correlation suggests that neither egg quantity nor egg mass indicate future fitness for the offspring.
Larva
thumb|Larva
The larval period is separated into five distinct stages or instars. During the first three instars, the comma larvae have a cryptic appearance to avoid detection while they primarily stay on the underside of leaves.
Adult
Full-grown comma butterflies have a wingspan of about 45 mm or 1.8 inches. The name comma butterfly derives from the small white C-shaped marking resembling a comma on the underside of its wings. Due to their orange and dark brown/black appearance, the butterflies resemble fallen leaves when their wings are closed. Adults can also undergo one of two morphs: the directly developing morph or the diapausing morph. During the directly developing morph, the butterflies mature sexually at a rapid rate. Females undergoing this morph oviposit in the summer, leading the phase to also be referred to as the summer morph. Butterflies portraying the summer morph have light coloured undersides.
<gallery mode="packed">
File:Polygonia c-album MHNT CUT 2013 3 19 Grisolles Male Dos.jpg |Male
File:Polygonia c-album MHNT CUT 2013 3 19 Grisolles Male Ventre.jpg |Male underside
File:Polygonia c-album MHNT CUT 2013 3 19 Verdun sur Garonne Female Dos.jpg |Female
File:Polygonia c-album MHNT CUT 2013 3 19 Verdun sur Garonne Female Ventre.jpg |Female underside
</gallery>
Predators, parasites, and diseases
Predators
Because of their wide distribution around the world, comma butterflies have a variety of vertebrate and invertebrate predators, including blue tits, chickens, P. vanessae often oviposit in the larvae of butterflies such as P. c-album and Nymphalis antiopa.
Diseases
P. c-album are known to be infected by cytoplasmic virus diseases. The disease infection usually starts in the cytoplasm of the midgut and progresses throughout the foregut and hindgut as well.
Antipredator adaptations
Larva
The first three larval instars are camouflaged, the dark colours making the larvae less vulnerable to detection. In the fourth instar, the appearance of the larval body is relatively more colourful with white, black, and orange aposematic patterns. A white stripe along its back mimics the pattern of bird droppings, further displaying protective colouration of the species.
Population change
In the 19th century, the British population of the comma crashed, possibly as a result of reduced hop (H. lupulus) farming. From about 1930 the population recovered, and the comma is now one of the more familiar butterflies in Southern England. It is also found in Scotland and in North Wales. Since the 1970s in Britain, specialist butterflies have decreased in population as their preferred habitat and host plants area becomes smaller. On the other hand, generalist species such as P. c-album have started to expand their range. In particular, comma butterflies have expanded along the northern edge of their range.
References
Further reading
External links
- Polygonia c-album at Fauna Europaea