Tetramorium robertsoni

Other than showing a preference for open areas, little is known about the biology of Tetramorium robertsoni.

Identification
The following character combination distinguishes Tetramorium robertsoni from other members of the complex: CI 93 - 94; antennal scapes moderate (SI 78 - 81); eyes moderate to large (OI 25 - 28); metanotal groove in profile barely impressed; mandibles unsculptured, smooth and shiny; median area of clypeus unsculptured; all dorsal surfaces with simple long, erect to suberect hairs; colour uniformly brown. T. robertsoni has a median area of the clypeus that is unsculptured and its metanotal groove barely impressed in profile, while Tetramorium edouardi has a clypeus with longitudinal rugulation, strongly developed median ruga and a distinctly impressed metanotal groove. Another morphologically related species is Tetramorium rubrum although its possession of a noticeably longer antennal scape (SI 85 - 93) and head (CI 87 - 91) separate it from T. robertsoni (SI 78 - 83, CI 92 - 95). Also, both species occur far apart from each other since T. rubrum occurs only in West Africa while T. robertsoni is only known from Tanzania. Additionally, T. robertsoni can be easily discriminated from Tetramorium philippwagneri and Tetramorium schoutedeni since the latter two have relatively small eyes (OI 21 - 22) and are distinctly bicoloured, whereas T. robertsoni shows larger eyes (OI 25 -28) and an uniform coloration. Finally, the simple hairs of T. robertsoni distinguish it clearly from the species with bizarre pilosity (Tetramorium pinnipilum, Tetramorium rogatum, Tetramorium zonacaciae), or without any standing hairs on mesosoma, waist segments, and gaster (Tetramorium mkomazi).

A member of the Afrotropical edouardi species complex, which is part of the weitzeckeri species group.

Key to weitzeckeri-group species.

Distribution
Known only from a few localities in Tanzania.

Distribution based on Regional Taxon Lists
Afrotropical Region: Tanzania.

Nomenclature

 *  robertsoni. Tetramorium robertsoni Hita Garcia, Fischer & Peters, 2010b: 33, figs. 23A, 37-39 (w.) TANZANIA.

Worker
HL 0.800 - 0.906 (0.849); HW 0.744 - 0.844 (0.794 ); SL 0.589 - 0.700 (0.647); EL 0.189 - 0.222 (0.206); PW 0.589 - 0.689 (0.637); WL 0.967 - 1.222 (1.098); PSL 0.244 - 0.339 (0.301); PTL 0.211 - 0.289 (0.249); PTH 0.300 - 0.378 (0.334); PTW 0.267 - 0.367 (0.311); PPL 0.256 - 0.300 (0.276); PPH 0.311 - 0.389 (0.343); PPW 0.367 - 0.444 (0.395); CI 92 - 95 (94); SI 78 - 83 (81); OI 25 - 28 (26); PSLI 31 - 39 (35); PeNI 44 - 55 (49); LPeI 68 - 80 (74); DPeI 119 - 132 (125); PpNI 60 - 67 (62); LPpI 74 - 86 (81); DPpI 132 - 156 (143); PPI 121 - 138 (128) (8 measured).

Head slightly longer than wide (CI 92 - 95). Anterior clypeal margin with small but distinct median impression. Frontal carinae strongly developed, less strongly developed behind eye level, ending shortly before posterior margin of head. Antennal scrobe shallow, narrow, and without defined posterior and ventral margins, ending before posterior margin of head. Antennal scape of medium size, not reaching posterior margin of head (SI 78 - 83). Eyes moderate to relatively large (OI 25 - 28), with 10 to 12 ommatidia in longest row. In lateral view metanotal groove not or barely impressed. Propodeal spines long and spinose (PSLI 31 - 39). Propodeal lobes small, triangular and acute. Petiolar node high nodiform, in dorsal view slightly wider than long (DPeI 119 - 132), in profile around 1.2 to 1.4 times higher than long (LPeI 68 - 80). Postpetiole in dorsal view between 1.2 to 1.6 times wider than long (DPpI 132 - 156); in lateral view rounded, around 1.1 to 1.3 times higher than long (LPpI 74 - 86). Mandibles unsculptured, smooth and shiny. Clypeus few rugae laterally, median area unsculptured and shiny. Head mostly longitudinally rugose with 7 to 8 widely spaced longitudinal rugae between frontal carinae, running unbroken to posterior margin of head. Mesosoma with mostly longitudinal rugulation, propodeal declivity unsculptured. Ground sculpturation on head and mesosoma smooth and shiny. Petiole and postpetiole mostly longitudinally rugose; gaster completely unsculptured, smooth and shiny. All dorsal surfaces of head, mesosoma, petiole, postpetiole, and gaster with many long, simple, suberect to erect hairs. Fine pubescence on antennal scapes and tibiae decumbent to suberect. Coloration brown, appendages of lighter colour.

Type Material
Holotype worker, TANZANIA, Mkomazi Game Reserve, Ibaya, 03° 58' S, 37° 48' E, savanna, unburnt slope, ex pitfall trap, 14.XI.1994, leg. A. Russell-Smith (: ZFMK_HYM_2009_6090). Paratypes, 2 workers with same data as holotype (BMNH: ZFMK_HYM_2009_6089, ZFMK_HYM_2009_6091); 5 workers from TANZANIA, Amani, 850m, 9.XI.1957, leg. E.S. Ross & R.E. Leech (: 4 workers CASENT0218274, CASENT0218276, CASENT0218277, CASENT0218278; ZFMK: 1 worker CASENT0218275).

Etymology
This species is dedicated to Dr. Hamish G. Robertson from South Africa in honour of his work in Afrotropical myrmecology.