Tetramorium xanthogaster Santschi 1911

Tetramorium sikorae var. xanthogaster Santschi, 1911e PDF: 124 (w.) MADAGASCAR. Malagasy. Primary type information: MADAGASCAR, coll. M.J. de Gaulle; CASENT0101146; NHMB AntCat AntWiki HOL

Taxonomic history

[Original spelling of Tetramorium xantogaster justifiably emended to Tetramorium xanthogaster by Wheeler, 1922: 1032.].Raised to species: Bolton, 1979 PDF: 139.See also Hita Garcia & Fisher, 2014c PDF: 150.

(Figs 3, 4)

Tetramorium (Xyphomyrmex) [sic] sikorae st. xantogaster [sic] Santschi, 1911: 124. Holotype worker, Madagascar {J. de Gaulle) (NM, Basle) [examined]. Xiphomyrmex sikorae subsp. xanthogaster Santschi ; Wheeler, 1922: 1032. Emery, 1922: 287 [justified emendation].

Worker. TL 3.2, HL 0.76, HW 0.66, CI 89, SL 0.54, SI 82, PW 0.50, AL 0.88.

Mandibles smooth with scattered small pits. Median clypeal carina very faint, almost effaced, much less distinct than the lateral carinae. Frontal carinae very reduced, their posterior extensions fine and no more distinct than the rugulae between them. Antennal scrobes absent. Metanotal groove not impressed. Propodeum armed with a pair of short, stout spines, the metapleural lobes roughly triangular. Dorsum of head with very fine, faint, irregular longitudinal rugulae and with a superficial reticulate ground sculpture between them. Dorsal alitrunk with scattered, weak, predominantly longitudinal rugulae. Pedicel and gaster unsculptured, smooth and polished. All dorsal surfaces of head and body with erect or suberect fine hairs. Head and alitrunk dark brown, pedicel and gaster clear pale yellow, the two strongly contrasting.

As Santschi pointed out in the original description, this small species is close to sikorae , but unlike that species it is bicoloured, has relatively longer antennal scapes, lacks scrobes and has much better developed propodeal spines. The presence of gastral pilosity places this species in the sikorae-complex of the schaufussi-group, but the characters given above will quickly separate xanthogaster from its allies.

Head clearly longer than wide (CI 92–94); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae weakly developed, only faintly raised, usually becoming much weaker around eye level and fading out halfway between posterior eye margin and posterior head margin. Antennal scrobes very weak, shallow and without clear and distinct posterior and ventral margins. Antennal scapes short, not reaching posterior head margin (SI 70–75). Eyes moderate to relatively large (OI 22–25). Mesosomal outline in profile flat to weakly convex, comparatively low and long (LMI 36–39), weakly to moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove weakly developed or absent. Propodeal spines/teeth very short to short, varying from triangular and blunt to elongate-triangular and acute (PSLI 10–16), propodeal lobes short, triangular, and blunt, always much shorter than propodeal spines, spines and lobes not strongly inclined towards each other. Petiolar node in profile high nodiform, nodiform or weakly cuneiform, always with relatively well rounded antero- and posterodorsal margins, around 1.5 to 1.7 times higher than long (LPeI 59–67), anterior and posterior faces often approximately parallel and often not, anterodorsal and posterodorsal margins usually at about same height, sometimes anterodorsal margin situated slightly higher than posterodorsal, petiolar dorsum weakly to moderately convex; petiolar node in dorsal view around 1.2 to 1.3 times wider than long (DPeI 119–133), in dorsal view pronotum between 2.2 to 2.7 times wider than petiolar node (PeNI 37–46). Postpetiole in profile globular to subglobular, approximately 1.3 to 1.5 times higher than long (LPpI 68–80); in dorsal view around 1.3 to 1.4 times wider than long (DPpI 125–140), pronotum between 1.8 to 2.1 times wider than postpetiole (PpNI 48–56). Postpetiole in profile appearing more or less as voluminous as petiolar node, postpetiole in dorsal view around 1.2 to 1.3 times wider than petiolar node (PPI 117–129). Mandibles unsculptured, smooth, and shining; generally sculpture on clypeus very much reduced, median area usually unsculptured with one or two weak, irregular, and broken rugulae laterally, very rarely median rugula present but then weak and broken; cephalic dorsum between frontal carinae irregularly longitudinally rugulose with six to eight widely separated rugulae, rugulae running from posterior clypeal margin to posterior head margin, but irregularly shaped, often broken or with cross-meshes, and becoming weaker or fading out towards posterior head margin; scrobal area partly unsculptured, but mostly merging laterally with surrounding reticulate-rugose to longitudinally rugose sculpture present around eyes, most of lateral head predominantly unsculptured, smooth, and shiny; ground sculpture on head weakly to moderately punctate. Dorsum of mesosoma weakly to moderately longitudinally rugulose, sometimes irregularly so, often rugulae very weak and parts of dorsal mesosoma smooth; lateral mesosoma anteriorly often only weakly sculptured and shiny, katepisternum and lateral propodeum usually irregularly longitudinally rugulose to reticulate-rugose, sometimes almost completely unsculptured, smooth, and shiny; ground sculpture on mesosoma usually only weakly developed, mostly absent. Forecoxae unsculptured, smooth, and shining. Waist segments and gaster unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; dorsum of promesonotum always with more than ten pairs of long, standing hairs, propodeum usually with one or two pairs, sometimes with up to five, rarely without any standing pilosity; waist segments each with several pairs; first gastral tergite with short, scarce to moderately abundant, appressed to decumbent pubescence in combination with scattered, long, standing hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with decumbent to subdecumbent hairs. Body colour variable, usually bicoloured with head and mesosoma of dark brown to blackish colour contrasting with yellowish or light brown appendages, waist segments, and gaster; very rarely only head of dark brown contrasting with yellowish remainder of body, sometimes body uniformly coloured, ranging from yellow to dark brown.

Tetramorium xanthogaster has a relatively patchy distribution range (Fig. 66). The southernmost locality is Analavelona in the southwest. The next known localities are located in the Central Highlands much further north and east (Ambohitantely, Ankokoy, and Marotandrano). The remaining localities are situated in the northern part of Madagascar (Andranobe, Marojejy, Binara, Montagne d’Ambre, and Manongarivo). Many of these localities are widely separated from each other. Furthermore, it seems that Tetramorium xanthogaster prefers montane rainforests since most collections are from elevations around or above 1000 m, whereas it was only occasionally collected from lower elevations. An explanation for the currently patchy distribution records could be that Tetramorium xanthogaster nests and/or forages in the vegetation since almost all of the available material was collected either from beating low vegetation or Malaise traps. Consequently, we expect that more collecting in the lower vegetation stratum will likely yield more material of this species.