Tetramorium rala Hita Garcia & Fisher

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 : 97-100

Tetramorium rala Hita Garcia & Fisher sp. n. Figs 43A, 55, 65

Type material.

Holotype, pinned worker, MADAGASCAR, Antsiranana, Parc National de Marojejy, Manantenina River, 28.0 km 38° NE Andapa, 8.2 km 333° NNW Manantenina, 14.43667°S, 49.775°E, 450 m, rainforest, sifted litter (leaf mold, rotten wood), collection code BLF08722, 12.-15.XI.2003 (B.L. Fisher et al.) (CAS: CASENT0046163). Paratypes, five pinned workers with same data as holotype (BMNH: CASENT0046035; CAS: CASENT0045975; CASENT0046039; CASENT0046049; MCZ: CASENT0046176); and nine pinned workers with same data as holotype except sampled from rotten log and collection code BLF08772 (CAS: CASENT0077304; CASENT0077305; CASENT0077306).

Non-type material.

MADAGASCAR: Antsiranana, Cap Masoala, 19 km W Andampibe, 15.69361°S, 50.18167°E, 125 m, lowland rainforest, 2.XII.1992 (G.A. Alpert); Antsiranana, Makirovana forest, 14.17066°S, 49.95409°E, 415 m, rainforest, 28.-29.IV.2011 (B.L. Fisher et al.); Antsiranana, Makirovana forest, 14.16044°S, 49.95216°E, 550 m, rainforest, 1.V.2011 (B.L. Fisher et al.); Antsiranana, Parc National de Marojejy, Manantenina River, 28.0 km 38° NE Andapa, 8.2 km 333° NNW Manantenina, 14.43667°S, 49.775°E, 450 m, rainforest, 12.-15.XI.2003 (B.L. Fisher et al.); Antsiranana, 15 km S Sambava, 10 m, 19.XII.1972 (J.-M. Bentsch); Fianarantsoa, Réserve Speciale Manombo 24.5 km 228° Farafangana, 23.01583°S, 47.719°E, 30 m, rainforest, 21.IV.2005 (B.L. Fisher et al.); Toamasina, 6.3 km S Ambanizana, Andranobe, 15.6813°S, 49.958°E, 25 m, rainforest, 14.XI.1993 (B.L. Fisher); Toamasina, 5.3 km SSE Ambanizana, Andranobe, 15.67133°S, 49.97395°E, 425 m, rainforest, 21.XI.1993 (B.L. Fisher); Toamasina, Réserve Spéciale Ambatovaky, Sandrangato river, 16.77274°S, 49.26551°E, 450 m, rainforest, 20.-22.II.2010 (B.L. Fisher et al.); Toamasina, Réserve Spéciale Ambatovaky, Sandrangato river, 16.76912°S, 49.26704°E, 475 m, rainforest, 21.II.2010 (B.L. Fisher et al.); Toamasina, Réserve Spéciale Ambatovaky, Sandrangato river, 16.7633°S, 49.26692°E, 520 m, rainforest, 22.II.2010 (B.L. Fisher et al.); Toamasina, 19 km ESE Maroantsetra, 15.48333°S, 49.9°E, 300 m, rainforest, 22.IV.1989 (P.S. Ward); Toamasina, Nosy Mangabe, 15.5°S, 49.76667°E, 20-50 m, rainforest, 20.IV.1989 (P.S. Ward); Toamasina, F.C. Sandranantitra, 18.04833°S, 49.09167°E, 450 m, rainforest, 18.-21.I.1999 (H.J. Ratsirarson); Toamasina, S.F. Tampolo, 10 km NNE Fenoarivo Atn., 17.2825°S, 49.43°E, 10 m, littoral rainforest, 4.IV.1997 (B.L. Fisher).

Diagnosis.

The following character combination distinguishes Tetramorium rala from the remainder of the Tetramorium schaufussii species complex: relatively small species (HW 0.46-0.49; WL 0.58-0.64); eyes relatively large (OI 26-28); antennal scapes very short (SI 61-68); frontal carinae usually very weakly developed, only feebly raised, usually ending shortly after posterior eye margin or merging with cephalic sculpture halfway between posterior eye margin and posterior head margin; propodeal spines medium-sized to long, elongate-triangular to spinose, and acute (PSLI 21-25), propodeal lobes short, triangular, and acute or blunt, but always much shorter than propodeal spines, spines and lobes not strongly inclined towards each other; petiolar node in profile high rounded nodiform to thinly cuneiform, in profile 2.0 to 2.2 times higher than long (LPeI 45-50), in dorsal view around 1.3 to 1.5 times broader than long (DPeI 129-145); mesosoma with three to four pairs on dorsal promesonotum, propodeum and waist segments without any standing pilosity; body uniformly whitish yellow to light brown.

Worker measurements

(N=15). HL 0.49-0.53 (0.51); HW 0.46-0.49 (0.47); SL 0.28-0.33 (0.31); EL 0.12-0.13 (0.13); PH 0.22-0.24 (0.23); PW 0.32-0.37 (0.35); WL 0.58-0.64 (0.61); PSL 0.11-0.13 (0.12); PTL 0.09-0.11 (0.10); PTH 0.20-0.23 (0.21); PTW 0.13-0.16 (0.14); PPL 0.12-0.14 (0.13); PPH 0.18-0.21 (0.19); PPW 0.18-0.22 (0.19); CI 90-94 (92); SI 61-68 (65); OI 26-28 (27); DMI 52-60 (57); LMI 36-39 (37); PSLI 21-25 (23); PeNI 37-43 (40); LPeI 45-50 (49); DPeI 129-145 (136); PpNI 52-59 (54); LPpI 67-75 (70); DPpI 141-157 (148); PPI 129-142 (138).

Worker description.

Head clearly longer than wide (CI 90-94); posterior head margin weakly concave, almost straight. Anterior clypeal margin with distinct median impression. Frontal carinae usually very weakly developed, only feebly raised, usually ending shortly after posterior eye margin or merging with cephalic sculpture halfway between posterior eye margin and posterior head margin. Antennal scrobes very weak to absent, very shallow and without clear and distinct posterior and ventral margins. Antennal scapes very short, not reaching posterior head margin (SI 61-68). Eyes relatively large (OI 26-28). Mesosomal outline in profile flat to weakly convex, comparatively low and long (LMI 36-39), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove very weak to absent. Propodeal spines medium-sized, elongate-triangular to spinose, and acute (PSLI 21-25), propodeal lobes short, triangular, and acute or blunt, but always much shorter than propodeal spines, spines and lobes not strongly inclined towards each other. Petiolar node in profile high rounded nodiform to thinly cuneiform, around 2.0 to 2.2 times higher than long (LPeI 45-50), anterior and posterior faces not parallel, anterodorsal margin usually situated higher and more strongly angled than posterodorsal margin, petiolar dorsum relatively flat to weakly convex and tapering backwards posteriorly; node in dorsal view around 1.3 to 1.5 times broader than long (DPeI 129-145), in dorsal view pronotum between 2.3 to 2.7 times wider than petiolar node (PeNI 37-43). Postpetiole in profile globular to subglobular, approximately 1.3 to 1.5 times higher than long (LPpI 67-75); in dorsal view around 1.4 to 1.6 times wider than long (DPpI 141-157), pronotum between 1.7 to 1.9 times wider than postpetiole (PpNI 52-59). Postpetiole in profile lower, thicker, and more rounded than petiolar node, postpetiole in dorsal view around 1.3 to 1.4 times wider than petiolar node (PPI 129-142). Mandibles completely unsculptured, smooth, and shiny; clypeus longitudinally rugulose with three to five rugulae, median rugula always present and usually fully developed, one or two mostly entire, rarely broken, lateral rugulae present on each side; cephalic dorsum between frontal carinae irregularly longitudinally rugulose with seven to ten fine rugulae, rugulae usually running from posterior clypeal margin to posterior head margin, but mostly irregularly shaped, interrupted or with cross-meshes; scrobal area mostly unsculptured; lateral head mainly longitudinally rugulose to reticulate-rugulose, but larger areas often only weakly sculptured and appearing fairly smooth and shiny; ground sculpture on head weakly to moderately punctate. Dorsum of mesosoma ranging from weakly longitudinally rugulose with larger areas with almost completely reduced sculpture to longitudinally rugose with well developed rugae; lateral mesosoma weakly to moderately irregularly longitudinally rugulose or reticulate-rugulose, often with larger areas of almost completely reduced sculpture; ground sculpture on mesosoma usually weak to absent, sometimes moderately punctate. Forecoxae, both waist segments, and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; mesosoma with three to four pairs on promesonotum; propodeum and waist segments without any standing pilosity; first gastral tergite with short, moderately dense, appressed (rarely decumbent) pubescence combined with several scattered, long, fine erect to suberect hairs; anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed to decumbent hairs. Body uniformly whitish yellow to light brown.

Etymology.

The new species is named after the fictional character “Rala” from Walter Moers’ fantasy novel "Rumo and His Miraculous Adventures". The species epithet is an arbitrary combination of letter, thus invariable.

Distribution and biology.

The distribution range of Tetramorium rala is relatively disjunctive (Fig. 65). Its main distribution seems to be in the northeast in the area around the Bay of Antongil and the Masoala Peninsula north to Marojejy and Makirovana. Further south of this main cluster of localities Tetramorium rala is only known from three additional places: Ambatovaky, Tampolo, and Manombo. One explanation for this patchy distribution would be a preferense for lowland rainforests. Tetramorium rala lives in rainforests and littoral forests at lower elevations ranging from 10 to 550 m where it is found in leaf litter. Very few intact lowland rainforests remain south of its main distribution in the northeast of Madagascar.

Discussion.

Tetramorium rala is a very distinctive member of the Tetramorium schaufussii complex due to its smaller size, relatively long propodeal spines, high nodiform to thinly cuneiform petiolar node, lack of standing pilosity on the waist segments, and very bright body colouration. Consequently, it is very unlikely to be confused with any other species. Most species are much larger in body size, have shorter propodeal spines, and/or possess standing pilosity on the waist segments. Only some smaller specimens of Tetramorium schaufussii could at first glance be mistaken with Tetramorium rala , but these two species are effortlessly separable. Tetramorium schaufussii has much shorter propodeal spines (PSLI 11-18), a lower petiolar node, which in profile is only 1.6 to 1.9 times higher than long (LPeI 52-63), and long, standing pilosity on the waist segments. By contrast, in Tetramorium rala the propodeal spines are much longer (PSLI 21-25), the petiolar node is higher, in profile around 2.0 to 2.2 higher than long (LPeI 45-50), and the waist segments lack standing pilosity.

However, even though Tetramorium rala is easily identifiable within the Tetramorium schaufussii complex, it is morphologically very close to Tetramorium rumo from the Tetramorium cognatum complex since they share a very similar gestalt. Both species are smaller in size, have relatively longer propodeal spines (compared to most other species of the species group), a high nodiform to thinly cuneiform petiolar node, lack standing pilosity on the waist segments, and possess very bright body colouration. The main separating character, which also places them in separate species complexes, is the lack of standing pilosity on the first gastral tergite in Tetramorium rumo versus the presence of standing pilosity on the first gastral tergite in Tetramorium rala . Both species are morphologically closer to each other than to any other species of the Tetramorium schaufussii species group, but there are highly diagnostic differences to support their heterospecificity. The petiolar node of Tetramorium rumo is thinner and stronger anteroposteriorly compressed, in profile around 2.3 to 2.7 times higher than long (LPeI 37-43), and in dorsal view between 1.5 to 1.7 times wider than long (DPeI 156-171), whereas Tetramorium rala has a node which in profile is 2.0 to 2.2 times higher than long (LPeI 45-50), and in dorsal view around 1.3 to 1.5 times broader than long (DPeI 129-145). In addition, Tetramorium rumo also has larger eyes (OI 28-31) than Tetramorium rala (OI 26-28). Further evidence of their heterospecifity can be deduced from their distribution ranges, which overlap in central-eastern Madagascar, but both species maintain their species-specific characteristic without intermediate forms. In Manombo both species were also found living in sympatry in close proximity.