Leptogenys angusta

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Leptogenys angusta
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Ponerinae
Tribe: Ponerini
Genus: Leptogenys
Species group: attenuata
Species: L. angusta
Binomial name
Leptogenys angusta
(Forel, 1892)

Leptogenys angusta casent0101798 profile 1.jpg

Leptogenys angusta casent0101798 dorsal 1.jpg

Specimen labels

Collections for L. angusta have been made from litter sifting, malaise, pitfall, and yellow pan traps. Whereas some individual worker specimens search for prey on the ground, others have been observed foraging on lower vegetation. Colony nests of this species have been found in rotten logs and in rotten branches on the ground. One colony was found with a staphyliniid beetle belonging to the subfamily Pselaphinae. (Rakotonirina and Fisher 2014)

Identification

A member of the attenuata species group. Rakotonirina and Fisher (2014) - Third antennal segment noticeably long, more than twice the length of second segment; eye large, breaking line of side of head, maximum diameter about one third the length of lateral cephalic margin; in dorsal view mesonotum as long as broad and petiolar node remarkably elongate and strongly narrowed anteriorly; antenna and leg elongate (SI: 163–203).

Leptogenys angusta is one of the largest species in the attenuata group in Madagascar. Compared to the maximum diameter of the eye of Leptogenys zohy, which is less than the maximum diameter of the scape, that of L. angusta is twice as wide as the widest part of the scape. Leptogenys johary has a much shorter third antennal segment that is twice as long as the second while L. angusta has a much longer third antennal segment that is more than twice as long as the second. Leptogenys angusta is comprised of two morphological variants. The larger form is characterized by a much more elongate head that slightly increases in width anteriorly and by a much larger eye (maximum diameter one third the length of side of head). The second is recognized by its smaller size, shorter head, very weakly diverging sides anterior to eye level, and smaller eye with a diameter between one third and one fourth the length of the lateral cephalic border. It is important to note that intermediates between these two forms have been encountered.

Keys including this Species

Distribution

Distribution based on Regional Taxon Lists

Malagasy Region: Madagascar (type locality).

Distribution based on AntMaps

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Distribution based on AntWeb specimens

Check data from AntWeb

Habitat

This species is widely distributed in the humid forests of eastern Madagascar. However, the species is also found on the grassland in Ambatovy and in tropical dry forest in Antsahabe Daraina, adjacent to montane forests and lowland rainforests. The two morphs within the species segregate across environmental gradients, suggesting that different selection pressures are at work among these different habitats. The larger form occurs generally in the lower altitude of the northeastern forests of Madagascar while the smaller form is known from the montane forest in the central-east to south-east of the island.

Biology

The Leptogenys genus page has more details about the general biology of ants in this genus. The following synopsis provided by Rakotonirina and Fisher (2014) offers an overview of the Malagasy Leptogenys: Recent surveys of arthropods in the Malagasy region uncovered a wealth of new species and showed that Leptogenys is one of the dominant ponerine ants widely distributed across all types of forest habitats. Workers are usually found foraging on the forest floor or in the leaf litter and only rarely on vegetation. They nest terrestrially under the soil, rocks, logs, or rootmat ground layers and in rotten logs, branches, in rotting bamboo, and rotten tree stumps. Most of the Malagasy species are endemic to Madagascar. In all Malagasy species, winged queens are absent, which limits their ability to disperse across the complex topography and various ecological barriers in the region. In the absence of alate queens, reproduction of Leptogenys in the region may be by fission, which enhances population viscosity and may result in important morphological variation across a species' geographic range. Though queens do not fly, males of Leptogenys are alate and are one of the most frequently collected ant genera in Malaise traps throughout Madagascar. Leptogenys exhibits a wide range of phenotypic diversity segregated both among spatially isolated habitats and along continuous environmental gradients.

Castes

Worker

Nomenclature

The following information is derived from Barry Bolton's New General Catalogue, a catalogue of the world's ants.

  • angusta. Lobopelta angusta Forel, 1892k: 519 (w.) MADAGASCAR. Combination in Leptogenys (Lobopelta): Emery, 1911d: 101. See also: Bolton, 1975a: 296.

Unless otherwise noted the text for the remainder of this section is reported from the publication that includes the original description.

Description

Worker

Rakotonirina and Fisher (2014) - (28 specimens). HW: 1.13–1.57, HL: 1.78–2.47, CI: 62–68, SL: 1.88–3.20, SI: 163–203, PW: 0.96–1.35, WL: 2.88–4.21, PNH: 0.70–1.00, PNL: 1.06–1.58, PNW: 0.49–0.78, DNI: 43–53, LNI: 59–72.

Head distinctly elongate, diverging anteriorly; posterior margin weakly concave medially. Basal angle of mandible obtus or with small tooth. In full-face view, eye large, maximum diameter twice as large as or greater than twice the maximum width of scape; usually breaking line of lateral border of head. Antennal scape long, apical half roughly surpassing posterior margin of head; third antennal segment markedly elongate, more than twice the length of the second. In dorsal view, mesonotum as long as broad. Propodeum with toothlike lobe or blunt angle on posterolateral margin; propodeal spiracle elliptical. Petiolar node elongate, in dorsal view more than twice as long as broad; anterior half strongly pinched laterally. Overall body relatively long. Mandible smooth with scattered piligerous punctures; most of body smooth and shining, except the lower half of lateral face of propodeum at level of propodeal spiracle, with occasional effaced transverse striation in profile. Dorsum of body with erect and suberect hairs: brown, longer and more robust on head and near base of scape, but yellow, shorter and more slender on mesosoma and gaster; pubescence present. Dorsum of head with paired hairs along midline. Coloration black to dark brown, with lighter appendages, and tip of gaster.

Queen

Rakotonirina and Fisher (2014) - (2 specimens): HW: 1.29–1.65, HL: 1.83–2.38, CI: 69–70, SL: 1.01–1.28, SI: 150–154, PW: 1.93–2.54, WL: 2.86–3.71, PNH: 0.76–1.02, PNL: 0.73–0.98, PNW: 0.68–0.84, DNI: 86–94, LNI: 103–105. Overall body of ergatoid queen shorter than that of worker; petiolar node as long as high in profile; gaster remarkably voluminous. Ocelli absent. Hairs numerous, erect hairs slender and pubescence longer.

Type Material

Rakotonirina and Fisher (2014) - Lectotype worker, present designation, Madagascar, Antananarivo Province, Andrangoloaka forest (Sikora), AntWeb CASENT0101834 (Musee d'Histoire Naturelle Genève). Paralectotypes: 2 workers, Toamasina, Moramanga, two workers on the same pin with specimen codes CASENT0101798, CASENT0101972 (MHNG) [examined].

References

  • Bolton, B. 1975a. A revision of the ant genus Leptogenys Roger (Hymenoptera: Formicidae) in the Ethiopian region with a review of the Malagasy species. Bull. Br. Mus. (Nat. Hist.) Entomol. 31: 235-305 (page 296, see also)
  • Emery, C. 1911e. Hymenoptera. Fam. Formicidae. Subfam. Ponerinae. Genera Insectorum 118: 1-125 (page 101, Combination in Leptogenys (Lobopelta))
  • Forel, A. 1892l. Nouvelles espèces de Formicides de Madagascar (récoltées par M. Sikora). Première série. Ann. Soc. Entomol. Belg. 36: 516-535 (page 519, worker described)
  • Rakotonirina, J.C. & Fisher, B.L. 2014. Revision of the Malagasy ponerine ants of the genus Leptogenys Roger (Hymenoptera: Formicidae). Zootaxa 3836, 1-163.