Leptogenys variabilis

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Leptogenys variabilis
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Ponerinae
Tribe: Ponerini
Genus: Leptogenys
Species group: attenuata
Species: L. variabilis
Binomial name
Leptogenys variabilis
Rakotonirina & Fisher, 2014

Leptogenys variabilis casent0022060 p 1 high.jpg

Leptogenys variabilis casent0022060 d 1 high.jpg

Specimen Labels

Leptogenys variabilis forages most often on the ground and in leaf litter but rarely on lower vegetation. Nest series have been collected frequently from rotten logs, under the soil, and beneath rocks. A few specimens have been found in rotten branches on the ground, under rootmat litter on rock, under rotten logs, and in rotting bamboo.

Identification

A member of the attenuata species group. Rakotonirina and Fisher (2014) - Worker. Third antennal segment of normal length, less than twice the length of the second; eye breaking outline of side of head; mandible smooth and shining apart from scattered piligerous punctures; in profile, lower half of propodeum from level of metathoracic spiracle and level of propodeal spiracle generally smooth. With petiole in profile, posterodorsal angle of node not projecting posteriorly nor overhanging posterolaterally; node longer than high (LNI: 91–105), anterior narrow ridge of junction to mesosoma attached directly to anterior face of node. In dorsal view, petiolar node longer and slim (DNI: 67–86), anterior portion distinctly but not strongly compressed laterally; yellowish-brown hairs on body dorsum.

Workers of Leptogenys fasika might be confounded with those of Leptogenys variabilis, but the former is larger (HW: 1.20–1.31, PW: 0.98–1.11), the antennal scape relatively longer and the petiolar node as long as high in profile; the node in dorsal view is more robust, without distinct lateral compression on the anterior portion; and the color of hairs on dorsum of body is whitish yellow. By contrast, L. variabilis workers are smaller (HW: 0.75–1.08, PW: 0.60–0.91) and have a shorter antennal scape; a much longer petiolar node in lateral view (LNI: 91–105) that is narrower with clearly laterally pinched anterior portion in dorsal view; hairs on body dorsum yellowish-brown.

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

The majority of samples have been recorded from dry forest habitats in western Madagascar, though a few specimens were collected in montane rainforests around which transitional habitats to either littoral rainforest or dry forests occurred.

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.

  • variabilis. Leptogenys variabilis Rakotonirina & Fisher, 2014: 60, figs. 19A, 23B, 26B, 30B, 71, 84 (w.q.) MADAGASCAR.

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

Variation. Leptogenys variabilis is one of the most highly variable taxa in the attenuata group. Its populations involve extensive variation of morphological characters and may encompass more than one species. In fact, we found two distinctive forms for this species, one of which has medium-sized worker specimens (HW: 0.90–1.06) and a distinctly elongate petiolar node (LNI: 91–96). The second form is smaller (HW: 0.75–0.89), with much shorter and robust petiolar node (LNI: 93–100). Erect hairs and pubescence on dorsum of the body of these two forms are light brown or brown. The two forms occur sympatrically in some localities such as RS Ambre, Montagne des Français, Ampombofofo, and Forêt d'Analabe, suggesting that these forms constitute separate species. However, these differences are not supported when morphological diversity across the species’ whole range is considered. Some worker specimens show intermediate forms of characters such as body size, and the shape of petiolar node, which has a tendancy to be much shorter and robust.

Description

Worker

(33 specimens). HW: 0.75–1.08, HL: 1.03–1.50, CI: 68–75, SL: 0.92–1.60, SI: 122–155, PW: 0.60–0.91, WL: 1.59–2.45, PNH: 0.49–0.79, PNL: 0.49–0.76, PNW: 0.37–0.63, DNI: 67–86, LNI: 91–105.

Head longer than broad, sides slightly diverging anteriorly and posteriorly rounding to more or less straight posterior margin. In full-face view, eye medium-sized, maximum diameter about one-fourth the length of lateral cephalic margin; breaking outline of lateral cephalic border. Antennal scape long, roughly one fourth its length extending over posterior margin of head. Third antennal segment normal, length less than twice the length of the second. In lateral view, propodeal lobe lacking. In profile, petiolar node clearly longer than high, anterior narrow ridge at junction to propodeum attached directly to anterior face of node, with no visible distance between them. In dorsal view, petiolar node elongate and slim, length less than twice its greatest width; anterior portion distinctly compressed laterally, width not gradually decreasing from rear to front. Mandible smooth apart from scattered hair pits; clypeus rugulose or with sparse punctures but never entirely smooth. Dorsum of head and body, lateral surface of mesosoma and declivitous surface generally smooth and shining. Yellowish-brown standing hairs and pubescence cover the head and body; lateral portion of body almost without erect hairs. Integument dark brown to black; appendages brown basally and yellow-orange on apical portion; tip of gaster lighter in color. Some specimens represent bluish or opalescent reflection.

Queen

(4 specimens). HW: 0.95–1.00, HL: 1.32–1.38, CI: 72–73, SL: 1.29–1.32, SI: 132–135, PW: 0.73–0.79, WL: 1.93–2.07, PNH: 0.60–0.63, PNL: 0.44–0.51, PNW: 0.53–0.58, DNI: 110–131, LNI: 118–139. Ergatoid queens and workers of L. variabilis are very similar to each other, but as usual head broader, antennal scape much shorter, erect hairs more slender and numerous, and gastral segments greatly enlarged for the queen; thoracic sclerites present but incomplete and finally petiolar node relatively broader in dorsal view and shorter than high in profile.

Type Material

Holotype worker: Madagascar, Mahajanga, PN Namoroka, 16.9 km 317° NW Vilanandro, -16.40667, 45.31, 100 m, tropical dry forest, ex rotten log, 12–16 Nov 2002 (Fisher, Griswold et al.) collection code: BLF06654, specimen code: CASENT0486515 (California Academy of Sciences). Paratypes: series of 8 workers, with same data as holotype but specimen coded: CASENT0486516. CASENT 0247272, CASENT0486514, CASENT0247208, CASENT0247207, CASENT0247206, CASENT0247205, CASENT0247204 (CASC, The Natural History Museum, Musee d'Histoire Naturelle Genève, Parc Botanique et Zoologique de Tsimbazaza).

References

  • Rakotonirina, J.C. & Fisher, B.L. 2014. Revision of the Malagasy ponerine ants of the genus Leptogenys Roger (Hymenoptera: Formicidae). Zootaxa 3836, 1-163.