Tetramorium cognatum Bolton 1979

Tetramorium cognatum Bolton, 1979 PDF: 135, figs. 1, 2 (w.q.) MADAGASCAR. Malagasy. Primary type information: MADAGASCAR, Toamasina, Perinet & vicinity, 18.82667°S, 48.44778°E, rainforest, rotten wood, 19.III.1969, coll. W.L. Brown; CASENT0102344; MCZC AntCat AntWiki HOL

Taxonomic history

See also Hita Garcia & Fisher, 2014c PDF: 68.

(Figs 1, 2)

Holotype worker. TL 2.8, HL 0.66, HW 0.56, CI 85, SL 0.42, SI 75, PW 0.44, AL 0.78.

Mandibles smooth, with scattered small pits. Anterior margin of clypeus with a shallow median impression, the clypeus with a pair of lateral carinae which are at least as strongly developed as the median. Frontal carinae extended back on head by a pair of weak ridges which are almost parallel, very slightly sinuate . Antennal scrobes feeble, scarcely impressed but as long as the scapes, the latter short. Corners of pronotum in dorsal view angular. Metanotal groove feebly impressed with the alitrunk in profile. Propodeum armed with a pair of short triangular spines, the metapleural lobes triangular and larger than the propodeal spines (in some specimens the two are subequal). Node of petiole high and narrow, rounded, in dorsal view slightly broader than long. Dorsum of head and promesonotum finely longitudinally rugulose, the rugulae irregular and tending to meander slightly, the spaces between the rugulae with a fine superficial sculpture of small punctures. Pedicel and gaster unsculptured. Dorsum of head and alitrunk with sparse pubescence and with a number of long, erect hairs (variable on propodeum, usually hairless but some with a single short pair laterad, immediately behind the metanotal groove). First gastral tergite with long and quite dense pubescence but without long hairs such as are seen on the head, alitrunk, and fringing the remaining gastral tergites. Colour mid-brown, the gaster slightly darker.

Paratype workers. As holotype but some more lightly and others more darkly coloured. The petiole node shows some variation and may be as broad as long in dorsal view. The range of dimensions noted is TL 2.5 - 2.8, HL 0.60 - 0.66, HW 0.54 - 0.58, CI 85 - 91, SL 0.36 - 0.42, SI 70 - 75, PW 0.40 - 0.44, AL 0.70 - 0.78 (10 measured).

Holotype worker, Madagascar: Perinei & vic., rain for. rot. wd., 19. iii. 1969, rain forest (W. L. Brown) (MCZ, Cambridge).

Paratypes. 11 workers with same data as holotype; 5 workers and 2 females with same data as holotype but 17. iii. 1969; 2 workers with same data as holotype but 18. iii. 1969 (MCZ, Cambridge; BMNH; MHN, Geneva; NM, Basle).

In the schaufussi-group the cognatum-complex of species is characterized by the lack of pilosity on the first gastral tergite but its retention on succeeding segments. In this complex are severini , proximum , cognatum and naganum . Of these severini is the most conspicuous, being larger than the rest (compare measurements) and having very reduced sculpture on the dorsal alitrunk. The other three species are distinctly smaller and the dorsal alitrunk is strongly rugulose or reticulaterugulose. T. naganum is distinguished by having numerous fine hairs on propodeum and pedicel segments which are absent in the other three members of this complex, although a single pair of fine short hairs is developed laterad immediately behind the metanotal groove in some samples of cognatum . Finally, cognatum is separated from proximum by the presence in the latter of dense short pubescence on the first gastral tergite which is slightly elevated, whilst in the former pubescence is minute, very sparse and strongly appressed.

It is interesting to note that ibycterum of the ranarum-group and latreillei of the tortuosumgroup have paralleled the members of this complex in losing the pilosity of the first gastral tergite, though what advantage is gained by suppressing the gastral hairs cannot be guessed at.

NON-PARATYPIC MATERIAL

Madagascar: no loc (Staudinger); vic. Andasibe (= Perinet) (W. L. & D. E. Brown); Parc Nat. Mont. d'Ambre (W. L. & D. E. Brown); La Mandraka (W. L. & D. E. Brown).

Head much longer than wide (CI 87–91); in full-face view posterior head margin usually very weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae weakly developed, only faintly raised, slightly diverging posteriorly, and relatively long, often ending shortly before posterior head margin. Antennal scrobes very weakly developed, shallow and without clear and distinct posterior and ventral margins. Antennal scapes very short, not reaching posterior head margin (SI 61–67). Eyes very large (OI 27–29). Mesosomal outline in profile flat to weakly convex, comparatively low and long (LMI 36–40), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove usually present, but relatively weak. Propodeal spines reduced to very short, triangular teeth (PSLI 12–16), propodeal lobes short and triangular, spines and lobes usually of approximately same length, often spines weakly shorter than lobes, very rarely spines weakly longer than lobes. Petiolar node in profile rounded high nodiform, around 1.8 to 2.0 times higher than long (LPeI 49–55), anterior and posterior faces approximately parallel, anterodorsal margin usually sharper than more rounded posterodorsal margin, both margins often situated at about same height, often anterodorsal margin slightly higher, petiolar dorsum usually weakly convex; node in dorsal view around 1.3 to 2 times wider than long (DPeI 129–142), in dorsal view pronotum between 2.3 to 2.7 times wider than petiolar node (PeNI 38–44). Postpetiole in profile globular, rarely subglobular, between 1.3 to 1.5 times higher than long (LPpI 66–75); in dorsal view around 1.3 to 1.5 times wider than long (DPpI 137–153), pronotum between 1.7 to 1.9 times wider than postpetiole (PpNI 53–59). Postpetiole in profile usually appearing shorter and less voluminous than petiolar node, postpetiole in dorsal view between 1.3 to 1.5 times wider than petiolar node (PPI 131–147). Mandibles completely unsculptured, smooth, and shiny; clypeus usually irregularly longitudinally rugulose, median ruga often unbroken and well developed, often partly reduced, and often fully absent; lateral rugulae ranging from one to three on each side, often irregularly shaped, broken, or reduced to traces; cephalic dorsum between frontal carinae longitudinally rugulose with six to ten fine rugulae, rugulae usually running from posterior clypeal margin to posterior head margin, mostly irregularly shaped, interrupted, meandering or with cross-meshes, and sometimes becoming much weaker posteriorly; scrobal area mostly unsculptured, merging with surrounding sculpture; lateral head reticulate-rugose to longitudinally rugose, often with larger areas of reduced sculpture; ground sculpture on head weakly to moderately punctate, sometimes completely absent. Dorsum of mesosoma irregularly longitudinally rugulose, sometimes weakly so; lateral mesosoma usually mostly irregularly longitudinally rugulose, lateral pronotum often much weaker-sculptured, almost smooth, and sometimes reticulate-rugulose; ground sculpture on mesosoma usually weakly to moderately punctate, sometimes completely absent. Forecoxae usually unsculptured, smooth and shining, sometimes with traces of ground sculpture dorsally. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of long, standing hairs, dorsal mesosoma normally with four to six (sometimes reduced to two to three) pairs occurring from anterior pronotum to metanotal groove, but absent from propodeum; waist segments and first gastral tergite without any long, standing hairs at all; first gastral tergite with moderately long, dense, appressed to decumbent pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed to subdecumbent hairs. Body colouration variable, ranging from uniformly bright yellow to very dark brown, if colour brown to dark brown, appendages usually lighter.

This species is one of the most common Tetramorium encountered in the rainforests and montane rainforests of Madagascar (Fig. 63). Its distribution range encompasses almost all sampled forests in eastern and northern Madagascar, as well as the isolated humid forests in central and western parts of the island (e.g. Ambohijanahary, Isalo). Surprisingly, Tetramorium cognatum also seems to do fairly well outside humid forests since it is also found in a few disturbed gallery forests, in Uapaca woodland and tropical dry forests, and very rarely in spiny forest/thicket and savannah/grassland. Additional sampling in arid habitats might show that Tetramorium cognatum is even more widely distributed than currently understood. The species was mostly collected from leaf litter and the ground.