Leptogenys oswaldi

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Leptogenys oswaldi
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Ponerinae
Tribe: Ponerini
Genus: Leptogenys
Species: L. oswaldi
Binomial name
Leptogenys oswaldi
(Forel, 1891)

Leptogenys oswaldi casent0101837 profile 1.jpg

Leptogenys oswaldi casent0101837 dorsal 1.jpg

The species forages both on lower vegetation and on the surface of the ground. Individual workers have been collected from litter sifting, in malaise traps, and with lights. Nest series have been found in rotten branches and dead branches above the ground, in rotten logs and beneath tree bark.

Identification

A member of the imerinensis complex of the incisa species group. Rakotonirina and Fisher (2014) - Worker. Mandible subtriangularly elongate and not strongly crossing when fully closed against clypeus; anteromedian lobe of clypeus broadly triangular; eye interrupting lateral cephalic border in full-face view of head; dorsum of head densely and finely reticulate-rugose.

Leptogenys oswaldi is the only species within the incisa group that has mandibles capable of closing tightly against the anteromedian lobe of the clypeus. This species can be confused with Leptogenys mayotte of Mayotte Island because its mandible is also capable of closing against the clypeus, but the eyes of L. oswaldi extend beyond the lateral cephalic border, whereas those of L. mayotte do not break the outline of the sides of the head.

In Madagascar, L. oswaldi is the only species of the ant genus Leptogenys that has an ecogeographic east-west distribution (cf. Vences and Glaw 2002; Yoder and Heckman, 2006), along which fairly pronounced morphological variation exists. Populations in the eastern humid forests are characterized by much longer standing hairs and abundant pubescence on the body, while populations inhabiting the dry forests of western Madagascar are covered with shorter erect hairs on the dorsum of the body and are almost without pubescence. Intermediates are found across the geographic range.

Keys including this Species

Distribution

Leptogenys oswaldi occurs in the northern half of Madagascar and its ranges from rainforest habitats in the east to the dry forests in the west of the island. This geographic distribution pattern demonstrates its ability to colonize a wide range of habitats including tsingy, dry, littoral, and humid forests.

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

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

Nomenclature

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

  • oswaldi. Lobopelta oswaldi Forel, 1891b: 119, pl. 4, fig. 2 (w.) MADAGASCAR. Combination in Leptogenys: Emery, 1911d: 102. See also: Bolton, 1975a: 297.

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) - (10 specimens). HW: 1.49–1.67, HL: 1.86–2.06, CI: 79–83, SL: 1.84–2.11, SI: 119–129, PW: 1.19–1.36, WL: 2.92–3.26, PNH: 0.84–0.96, PNL: 0.85–0.95, PNW: 0.75–0.97, DNI: 83–102, LNI: 93–103.

Head longer than wide and widest at mid-length immediately behind the level of eyes; lateral margin weakly convex throughout the length. Eye slightly protruding and breaking outline of side of head. Antennal scape relatively long (SI: 119–129). Median portion of clypeus projecting anteriorly into broad triangular lobe, bordered by a subopaque lamella, and having a pair of small, peg-like setae. Mandible long and narrow near base; blade distinctly widest at about apical third, where the inner margin forms a rounded or blunt basal angle; with preapical tooth approximately at apical fourth of length; capable of closing tightly against clypeus; basal groove broadly impressed. Hypostomal teeth not seen in cephalic full-face view. With mesosoma in dorsal view, metanotal groove impressed and with few cross-ribs; in profile, mesosoma relatively high and short; propodeal lobe absent or consisting of blunt angle; propodeal dorsum joining declivity with blunt angle. With petiole in profile, anterior face of node forming convex line with dorsal margin, terminating into distinct angle with anteriorly sloped posterior face. Constriction between third and fourth abdominal segments noticeably strong. FIGURE 105. Leptogenys oswaldi worker CASENT0496083. A: lateral view. B: head in full-face view. C: dorsal view. Mandible finely longitudinally striate, interspersed with few punctures. Dorsum of head in front of eye level longitudinally rugulose, and densely and finely reticulate-rugulose through posterior section; microreticulate sculpture with scattered punctures present near posterior border. Prontoum finely microreticulate, interspersed with sparse punctures; rest of mesosoma densely and finely reticulate-rugulose. Propodeal declivity either shagreened or transversely rugose. Dorsum of petiolar node and third abdominal tergite finely microreticulate superimposed with small punctures. Erect hairs short and robust, pubescence abundant on dorsum of body. Integument black, appendages black to dark brown near base and light brown to yellow at apical portion.

Type Material

Rakotonirina and Fisher (2014) - Holotype worker, Madagascar, Toamasina, 30 miles au Nord-Ouest de Tamatave (O’swald) AntWeb CASENT0101837 (Musee d'Histoire Naturelle Genève) [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 297, see also)
  • Emery, C. 1911e. Hymenoptera. Fam. Formicidae. Subfam. Ponerinae. Genera Insectorum 118: 1-125 (page 102, Combination in Leptogenys)
  • Forel, A. 1891c. Les Formicides. [part]. In: Grandidier, A. Histoire physique, naturelle, et politique de Madagascar. Volume XX. Histoire naturelle des Hyménoptères. Deuxième partie (28e fascicule). Paris: Hachette et Cie, v + 237 pp. (page 119, pl. 4, fig. 2 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.