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 initially classified as a subspecies of P. alcon, a European researcher, Lucien A. Berger, designated it as a separate species in 1946. Genetic similarities between P. rebeli and P. alcon have led many researchers to argue that the two are the same species and differences are due to intraspecific variation. Although P. rebeli is found across the Palearctic (see subspecies), it is difficult to determine the species' precise range due to confusion with P. alcon. Behavioral ecologists have found its role as a brood parasite to be of particular interest as, unlike many brood parasites, it does not directly oviposit in the hosts' nests. P. rebeli parasitizes the colony ant species Myrmica schencki as a larva by using chemical mimicry to trick the ants into believing that they are ant larvae; thus, the ants bring P. rebeli caterpillars back to their nests and feed them. P. rebeli is dependent on the plant Gentiana cruciata early in its life cycle and is vulnerable to parasitism by Ichneumon eumerus while inside the nest of M. schencki. It was placed on the IUCN Red List in 2000 and is classified as a species vulnerable to extinction.
Taxonomy The genus Phengaris was previously considered a subgroup within the genus Maculinea (explaining why P. rebeli was formerly known as M. rebeli) and the Maculinea-Phengaris clade is thought to be a section within Glaucopsyche. There are three groups within this Maculinea-Phengaris clade: the alcon group, the teleius group, and the Arion-Phengaris group. The groups are divided based on their alternative parasitization strategies of the host ants. The predatory strategy (in which the caterpillar consumes the host ants) and cuckoo strategy (in which the caterpillars feed off of the ants' regurgitation) are derived characteristics from the alcon group, with the predatory strategy having evolved from the teleius group and the cuckoo strategy having evolved from the arion-Phengaris group. Another way these groups are categorized is by whether or not they release a chemical (dorsal nectary organ secretions) to attract the attention of the host ant. This trait is not as prominent in ancestors of the alcon group and in M. nausithous, which is part of the teleius group. P. rebeli is most closely related to both subspecies of Phengaris alcon (P. alcon alcon and P. alcon kondakovi) with P. alcon alcon being more closely related to P. rebeli than to P. alcon kondakovi.
Subspecies Phengaris rebeli rebeli (Hirschke, 1904) Central and Southern Europe Phengaris rebeli cordidula (Jachontov, [1909]) Caucasus Major Phengaris rebeli imitator Tuzov, 2000 northern Tian-Shan, Dzungarian Alatau Phengaris rebeli kondakovi Kurentzov, 1970 Transbaikalia, Amur Oblast, Ussuri, northeast China Phengaris rebeli monticola (Staudinger, 1901) Armenia Phengaris rebeli ssp. Altai Mountains
Conflicts over classification Several researchers argue that P. rebeli has not evolved into a separate species from Phengaris alcon and that any variation between the two groups is due to intraspecific variation. Both species share a similar adult morphology, DNA and allozymes. Furthermore, they both have similar methods of parasitizing the host ant: they act as parasitic "cuckoos" within the ant nest and feed upon the ants' regurgitation. This is compared to the alternative method of predation used by Maculinea arion. To test this hypothesis, researchers examined how each species utilized the host ants. M. schencki and M. sabuleti are parasitized by P. rebeli while M. salina and M. vandeli are parasitized by P. alcon. M. scabrinodis is parasitized by both P. rebeli and P. alcon; however, P. alcon is far more likely than P. rebeli to parasitize M. scabrinodis. Researchers found that in general, P. alcon was far more likely to parasitize the host ant than P. rebeli; however, ant nests that supported P. alcon were much smaller and supported lower populations than ant nests that supported P. rebeli.
Appearance P. rebeli are noted for their large blue wings, with the males displaying a violet blue shade and the females displaying blue basal areas interspersed with brown spots, similar to other butterflies in the genus. The undersides of the wings are a dark brown with small black spots that are circled in white. This species can be distinguished from its close relative, P. alcon, by the broader black margins of the upper-side of wings of males and the extensive blue basal areas of wings of the females. It has a wingspan of approximately 32–36 mm.
Habitat It resides in fairly dry areas at lower elevations and damp meadows among trees at alpine elevation and is found in altitudes of 1000–2000 meters. Populations of P. rebeli are concentrated in the northern part of Portugal, Croatia and Greece, the western Pyrenees, France, and eastern part of Germany.
Lifecycle This butterfly begins life as eggs laid on leaves of Gentiana cruciata plants. The caterpillars hatch and feed upon the flowers and developing fruits of the plant. After feeding and growing for four instars, the caterpillars drop to the ground. There, the caterpillar releases chemicals which mimic the larvae of Myrmica ants. If an ant finds the caterpillar, it will carry the caterpillar back to its nest. Once inside the nest, the caterpillar tricks the ants into feeding and caring for it. P. rebeli pupates within the ant nest and crawls out as an adult.
Host plant P. rebeli choose where to lay their eggs based on the size of G. cruciata leaves and not upon the location of the closest Myrmica ant colony. This fact is supported by the timing of its oviposition. P. rebeli lays their eggs during the warm summer season, when Myrmica ants are most likely to be underground. Researchers also observed females did not base their oviposition on where they found Myrmica nests. Larger populations of G. cruciata are associated with higher production of flowers and seeds, but also with an increased frequency of P. rebeli feeding upon the plant. Researchers are particularly interested in the G. cruciata plant because both P. rebeli and G. cruciata are endangered. Lepidopterists have suggested that conservation of P. rebeli requires focus on conservation of G. cruciata.
Parasitism of ants
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