Tetramorium decem Forel, 1913a

Hita Garcia, Francisco & Fisher, Brian L., 2014, The ant genus Tetramorium Mayr in the Afrotropical region (Hymenoptera, Formicidae, Myrmicinae): synonymisation of Decamorium Forel under Tetramorium, and taxonomic revision of the T. decem species group, ZooKeys 411, pp. 67-103 : 77-80

Tetramorium decem Forel, 1913a comb. r. Figs 1A, 2A, 2B, 3, 6A, 8

Tetramorium (Decamorium) decem Forel, 1913a: 121. [Combination in Decamorium by Wheeler 1922: 906; senior synonym of Decamorium ultor by Bolton 1976: 298.]

Type material.

Lectotype [designated here], pinned worker, ZIMBABWE, Redbank, 19.98333S, 28.37759E, 7.IV.1912 (G. Arnold) (MHNG: CASENT0909196) [examined]. Paralectotypes [designated here], seven pinned workers with same data as lectotype (BMNH: CASENT0901035; MHNG: CASENT0248316; MSNG: CASENT0904789) [examined].

[Note: the GPS data of the type locality was not provided by the locality label or the original description. The data presented above is based on our own geo-referencing of the town of Redbank located in the Matabeleland North Province. Consequently, the location should be considered as an approximation and not the exact position of the type locality.]

Non-type material.

KENYA: Coastal Province, Malindi District, Arabuko Sokoke Forest, 3.28S, 39.97E, 75 m, Brachystegia forest, 26.V.2001 (R.R. Snelling & D.J. Martins); Coastal Province, Malindi District, Arabuko Sokoke Forest, 3.32111S, 39.92944E, ca. 50 m, VI.2009 (F. Hita Garcia & G. Fischer); TANZANIA: Mkomazi Game Reserve, Ibaya, 3.96667S, 37.8E, in burnt grassland, 19.-20.XI.1994 (A. Russel-Smith).

Diagnosis.

Tetramorium decem can be recognised by the following combination of characters: relatively larger species (HW 0.59-0.62; WL 1.02-1.16); propodeal teeth relatively longer (PSLI 17-19); petiolar node in profile around 1.2 to 1.3 times higher than long (LPeI 77-82); dorsum of promesonotum unsculptured, smooth, and very shiny; strongly bicoloured species with dark brown or black gaster contrasting with light brown to reddish brown remainder of body.

Worker measurements

(N=15). HL 0.71-0.74 (0.72); HW 0.59-0.62 (0.60); SL 0.42-0.45 (0.43); EL 0.19-0.21 (0.20); PH 0.33-0.37 (0.35); PW 0.47-0.50 (0.48); WL 1.02-1.16 (1.06); PSL 0.12-0.14 (0.13); PTL 0.25-0.27 (0.26); PTH 0.31-0.34 (0.33); PTW 0.22-0.24 (0.23); PPL 0.24-0.27 (0.25); PPH 0.32-0.36 (0.34); PPW 0.32-0.36 (0.34); CI 83-85 (84); SI 70-76 (72); OI 32-34 (33); DMI 41-47 (45); LMI 32-34 (33); PSLI 17-19 (18); PeNI 46-51 (48); LPeI 77-82 (80); DPeI 85-92 (88); PpNI 67-76 (70); LPpI 71-77 (75); DPpI 128-138 (133); PPI 143-149 (147).

Worker description.

Head much longer than wide (CI 83-85); posterior head margin weakly concave. Anterior clypeal margin with distinct, but often shallow median impression. Frontal carinae strongly developed and noticeably raised forming dorsal margin of very well-developed antennal scrobes, curving down ventrally and anteriorly halfway between posterior eye margin and posterior head margin and forming posterior and parts of ventral scrobe margins; antennal scrobes very well developed, deep and with clearly defined margins, but ventral margin less strongly developed, median scrobal carina absent. Antennal scapes short, not reaching posterior head margin (SI 70-76). Eyes very large (OI 32-34). Mesosomal outline in profile flat to weakly convex, relatively low and elongate (LMI 32-34), moderately to strongly marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove present, distinct, and clearly impressed. Propodeal spines short, elongate-triangular, and moderately acute (PSLI 17-19), propodeal lobes short, triangular, and usually blunt, always significantly shorter than propodeal spines. Tibiae and femorae strongly swollen. Petiolar node nodiform with moderately rounded antero- and posterodorsal margins, around 1.2 to 1.3 times higher than long (LPeI 77-82), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about the same height, petiolar dorsum clearly convex; node in dorsal view between 1.1 to 1.2 times longer than wide (DPeI 85-92), in dorsal view pronotum around 2.0 to 2.2 times wider than petiolar node (PeNI 46-51). Postpetiole in profile globular to subglobular, approximately 1.3 to 1.4 times higher than long (LPpI 71-77); in dorsal view around 1.3 to 1.4 times wider than long (DPpI 128-138), pronotum between 1.3 to 1.5 times wider than postpetiole (PpNI 67-76). Postpetiole in profile usually appearing less voluminous than petiolar node, postpetiole in dorsal view around 1.4 to 1.5 times wider than petiolar node (PPI 143-149). Mandibles and clypeus usually fully unsculptured, smooth, and shining, mandibles sometimes with few traces of rugulae apically; cephalic dorsum between frontal carinae mostly unsculptured and shiny, median ruga present and distinct, cephalic dorsum also puncticulate to punctate throughout its length, posteriorly close to posterior head margin especially pronounced; scrobal area partly unsculptured, smooth and shiny and partly merging with surrounding rugose sculpture on sides of head. Ground sculpture on head usually weak to absent. Dorsum of mesosoma mostly unsculptured, smooth and shiny with scattered punctures, rarely with few traces of rugulae; lateral mesosoma longitudinally rugose and very conspicuously reticulate-punctate except for mostly unsculptured lateral pronotum and katepisternum. Forecoxae unsculptured, smooth, and shining. Petiolar node and postpetiole superficially longitudinally rugulose or irregularly rugulose superimposed on conspicuous but relatively weak reticulate-punctate ground sculpture. Mesosoma and waist segments appearing mostly matt. First gastral tergite unsculptured, smooth, and shiny. Pilosity and pubescence greatly reduced: head with few pairs of moderately long, standing hairs, anterior pronotum with one long pair, waist segments sometimes with one long pair each, and sometimes first gastral tergite with one long pair; appressed pubescence present everywhere on body, but noticeable only on antennae, cephalic dorsum, legs, and first gastral tergite. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed hairs. Body strongly bicoloured with dark brown to black gaster contrasting with light brown to reddish brown remainder.

Distribution and biology.

The distribution range of Tetramorium decem is far smaller than previously thought (Fig. 3). Indeed, most of the material listed in the literature as Tetramorium decem or labelled as such in museum collections turned out to be either Tetramorium ultor or Tetramorium venator , while only a few collections proved to be genuine Tetramorium decem . Based on the redefined species definition, Tetramorium decem is only known from the type locality in Zimbabwe and two additional localities in East Africa: Arabuko Sokoke in Kenya and Mkomazi in Tanzania. Nevertheless, if more extensive sampling efforts are undertaken in East Africa, Tetramorium decem is likely to be found in more localities in Kenya, Tanzania, and Zimbabwe. Like Tetramorium uelense and Tetramorium ultor , Tetramorium decem prefers arid habitats, such as savannah and woodland. Based on Arnold (1917) and the collection label from some material from Arabuko Sokoke, Tetramorium decem nests in sandy soil. The diet consists of termites, as with most other members of the species group.

Discussion.

Tetramorium decem is the core species of the group, and was the type species for the description of the subgenus Decamorium by Forel (1913a). It is perhaps the most conspicuous species of the group. Its bicolouration, larger size, lack of sculpture on the mesosomal dorsum, and a higher petiolar node render it immediately recognisable. The mostly unsculptured, smooth and shiny mesosomal dorsum distinguishes Tetramorium decem from Tetramorium raptor and Tetramorium uelense , in which the dorsum of the mesosoma is clearly longitudinally rugose/rugulose. Tetramorium ultor and Tetramorium venator both share the lack of sculpture on the mesosomal dorsum with Tetramorium decem , but can still be easily separated from the latter. Tetramorium decem is generally larger in size (WL 1.02-1.16), has longer propodeal spines (PSLI 17-19) and is also conspicuously bicoloured, whereas Tetramorium ultor and Tetramorium venator are smaller species (WL 0.85-0.98) with significantly shorter propodeal teeth (PSLI 9-13) and a more uniform brown to black body colouration. In addition, Tetramorium decem also has a higher petiolar node, in profile around 1.2 to 1.3 times higher than long (LPeI 77-82), compared to the other two, in which the node in profile is only around 1.0 to 1.2 times higher than long (LPeI 86-100). The species that appears to be morphologically closest to Tetramorium decem is Tetramorium uelense . Both species share the large body, bicolouration, and preference for arid habitats. However, in addition to the sculpture on the mesosoma, Tetramorium uelense also has a lower petiolar node, in profile around 1.1 times higher than long (LPeI 88-93). Another character that is shared between Tetramorium decem and Tetramorium uelense but absent in the other species of the group is the development of the ventral margin of the antennal scrobe. In Tetramorium raptor , Tetramorium ultor , and Tetramorium venator the margin is clearly and well defined, while in Tetramorium decem and Tetramorium uelense it is less so and merges more with the surrounding rugose sculpture.

Variation.

Based on the available material we did not observe any significant form of intraspecific variation in Tetramorium decem .