Tetramorium naganum Bolton

Hita Garcia, Francisco & Fisher, Brian L., 2014, The hyper-diverse ant genus Tetramorium Mayr (Hymenoptera, Formicidae) in the Malagasy region taxonomic revision of the T. naganum, T. plesiarum, T. schaufussii, and T. severini species groups, ZooKeys 413, pp. 1-170 : 19-22

Tetramorium naganum Bolton Figs 1B, 2C, 4B, 9, 61

Tetramorium naganum Bolton, 1979: 150.

Type material.

Holotype, pinned worker, MADAGASCAR, Toamasina, La Mandraka, 18.912778°S, 47.892222°E 1280 m, montane forest, collection code AB41, 8.II.1977 (W.L. & D.E. Brown) (MCZ: MCZ_Holotype_32379) [examined]. Paratypes, 16 pinned workers and one dealate queen with same data as holotype (BMNH: CASENT0102346; CASENT0235212; MCZ: MCZ_Paratype_32379) [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 georeferencing of the rainforest locality La Mandraka and should be considered an approximation and not the exact location of the type locality of Tetramorium naganum .]

Non-type material.

MADAGASCAR: Antsiranana, Rés. Anjanaharibe-Sud, 6.5 km SSW Befingotra, 14.75°S, 49.5°E, 875 m, rainforest, 19.X.1994 (B.L. Fisher); Antsiranana, Rés. Anjanaharibe-Sud, 9.2 km WSW Befingotra, 14.75°S, 49.4667°E, 1280 m, montane rainforest, 5.XI.1994 (B.L. Fisher); Antananarivo, 3 km 41° NE Andranomay, 11.5 km 147° SSE Anjozorobe, 18.4733°S, 47.96°E, 1300 m, 5.-13.XII.2000 (B.L. Fisher et al.); Toamasina, 6.9 km NE Ambanizana, Ambohitsitondroina, 15.5851°S, 50.0095°E, 825 m, rainforest, 2.XII.1993 (B.L. Fisher); Toamasina, Ambanizana, Parc National Masoala, 15.5722°S, 50.0069°E, 1020 m, montane rainforest, 2.-6.III.2003 (D. Andriamalala et al.); Toamasina, Ambatoharanana, Corridor Forestier Analamay-Mantadia, 18.8042°S, 48.4008°E, 968 m, 12.-19.XII.2012 (B.L. Fisher et al.); Toamasina, Analamay, 18.8062°S, 48.3371°E, 1068 m, montane rainforest, 21.III.2004 (B.L. Fisher); Toamasina, Ankerana, 18.4017°S, 48.806°E, 1035 m, montane forest, 24.-29.I.2012 (B.L. Fisher et al.); Toamasina, Montagne d’Anjanaharibe, 19.5 km 27° NNE Ambinanitelo, 15.17833°S, 49.635°E, 1100 m, montane rainforest, 12.-16.III.2003 (B.L. Fisher).

Diagnosis.

Tetramorium naganum can be easily diagnosed within the Tetramorium naganum group on the basis of the following character combination: eyes small to moderate in size (OI 21-23); propodeal spines relatively long (PSLI 28-33); petiolar node in profile relatively thin, between 1.7 to 1.9 times higher than long (LPeI 54-58); waist segments with long, standing hairs; first gastral tergite with short, comparatively dense, appressed to decumbent pubescence, and without any long standing hairs.

Worker measurements

(N=10). HL 0.57-0.72 (0.63); HW 0.59-0.73 (0.65); SL 0.39-0.51 (0.46); EL 0.13-0.16 (0.14); PH 0.29-0.40 (0.33); PW 0.41-0.53 (0.45); WL 0.73-0.92 (0.78); PSL 0.18-0.22 (0.20); PTL 0.13-0.16 (0.14); PTH 0.24-0.28 (0.25); PTW 0.15-0.19 (0.16); PPL 0.18-0.22 (0.19); PPH 0.23-0.27 (0.24); PPW 0.23-0.28 (0.25); CI 94-99 (97); SI 68-77 (73); OI 21-23 (22); DMI 56-62 (58); LMI 40-45 (43); PSLI 28-33 (30); PeNI 34-38 (35); LPeI 54-58 (56); DPeI 107-122 (115); PpNI 52-59 (54); LPpI 77-84 (80); DPpI 125-137 (128); PPI 147-159 (153).

Worker description.

Head weakly to distinctly longer than wide (CI 94-99); posterior head margin moderately concave. Anterior clypeal margin with distinct median impression. Frontal carinae strongly developed, diverging posteriorly, and usually approaching or ending at posterior head margin; antennal scrobe present, but weak, shallow, and without defined posterior or ventral margins. Antennal scapes short, not reaching posterior head margin (SI 68-77). Eyes short to moderate (OI 21-23). Mesosomal outline in profile weakly convex, relatively high (LMI 40-45), and moderately to strongly marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent. Propodeal spines spinose, long, and acute (PSLI 28-33); propodeal lobes short, triangular, and blunt or acute, always much shorter than propodeal spines. Petiolar node in profile high, rounded nodiform, with well-rounded antero- and posterodorsal margins, between 1.7 to 1.9 times higher than long (LPeI 54-58), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about the same height (very rarely anterodorsal margin higher than posterodorsal margin) and equally marginate, petiolar dorsum always convex; node in dorsal view around 1.1 to 1.2 times wider than long (DPeI 107-122), in dorsal view pronotum between 2.7 to 3.0 times wider than petiolar node (PeNI 34-38). Postpetiole in profile globular, approximately 1.2 to 1.3 times higher than long (LPpI 77-84); in dorsal view between 1.2 to 1.4 times wider than long (DPpI 125-137), pronotum around 1.7 to 1.9 times wider than postpetiole (PpNI 52-59). Postpetiole in profile thicker and lower than petiolar node, postpetiole in dorsal view around 1.5 to 1.6 times wider than petiolar node (PPI 147-159). Mandibles variably sculptured, ranging from fully unsculptured, smooth, and shining through partially striate to fully striate; clypeus longitudinally rugose/rugulose, with two to six rugae/rugulae, median ruga always well developed and distinct, lateral rugae/rugulae usually weaker and/or interrupted; cephalic dorsum between frontal carinae with six to nine longitudinal rugae, rugae running from posterior clypeal margin to posterior head margin but very often irregular, interrupted or with cross-meshes, especially posteriorly; scrobal area usually mostly unsculptured, rarely longitudinally rugose to reticulate-rugose; lateral head longitudinally rugose to reticulate-rugose. Ground sculpture on head absent to weakly punctate. Mesosoma laterally and dorsally irregularly longitudinally rugose, rarely lateral mesosoma with a few unsculptured areas medially. Forecoxae unsculptured, smooth and shining. Ground sculpture on mesosoma very weak to absent. Waist segments and gaster completely unsculptured, smooth and shining. Head, mesosoma, and waist segments with numerous, long, and fine standing hairs; first gastral tergite with short, comparatively dense, appressed to subdecumbent pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae usually with decumbent to suberect hairs. Head, mesosoma, waist segments, and gaster usually orange to light brown, rarely of darker brown, mandibles, antennae, and legs always lighter, usually light yellowish brown.

Distribution and biology.

Tetramorium naganum is found in rainforests or montane rainforests in eastern and north-eastern Madagascar (Fig. 61). The distribution range is disjunctive, very much as in Tetramorium alperti and Tetramorium dalek . Tetramorium naganum is either found in the region around La Mandraka, Analamay, Andranomay, and Andasibe-Mantadia, and Ankerana, or much further north between Anjanaharibe-Sud and the Masoala Peninsula (Ambanizana), with Montagne d’Anjanaharibe being in-between. The reasons behind this discontinuous distribution are not clear yet, but as for Tetramorium alperti , it is likely that Tetramorium naganum was previously much more common in eastern Malagasy humid forests, and present-day populations represent only relict populations. The altitudinal range of the species with 825-1300 m supports this. However, since Tetramorium naganum is not particularly abundant or common where it occurs, it may just be a relatively rare faunal element in eastern Madagascar. If so, further sampling might yield additional material in the future, especially in the geographic areas between the two main populations mentioned above. Like most species in this group, Tetramorium naganum seems to be a leaf litter inhabitant.

Discussion.

Tetramorium naganum is the only species of the group that was known prior to our revision, and can be seen as the core species of the group. The lack of pilosity on the first gastral tergite isolates it fairly well from Tetramorium alperti and Tetramorium gilgamesh since these possess pilosity in varying degrees of inclination, length, and abundance. The relatively thin and high petiolar node (LPeI 54-58) separates Tetramorium naganum from Tetramorium alperti and Tetramorium enkidu , which have much thicker petiolar nodes (LPeI 60-68). Additionally, Tetramorium naganum has smaller eyes (OI 21-23) than Tetramorium gilgamesh (OI 25-27). The last species of the group, Tetramorium dalek , shares the lack of long, standing pilosity on the first gastral tergite with Tetramorium naganum . Nevertheless, both species are very unlikely to be confused with each other. Tetramorium dalek is generally smaller (HW 0.45-0.54; WL 0.54-68), has shorter propodeal spines (PSLI 25-27), and lacks long, standing hairs on the waist segments, whereas Tetramorium naganum is generally larger (HW 0.55-0.72; WL 0.66-0.92), possesses longer propodeal spines (PSLI 28-33), and always has long, standing hairs on the waist segments.