Tetramorium avaratra Hita, 2012

Hita Garcia, F. & B. L. Fisher, 2012, The ant genus Tetramorium Mayr (Hymenoptera: Formicidae) in the Malagasy region - taxonomic revision of the T. kelleri and T. tortuosum species groups., Zootaxa 3592, pp. 1-85 : 47-50

Tetramorium avaratra Hita Garcia & Fisher sp. n.

(Figs. 46, 47, 49, 102, 103, 104, 141)

Holotype worker, MADAGASCAR, Antsiranana, Réserve Spéciale de l'Ankarana, 22.9 km 224° SW Anivorano Nord, 12.90889 S, 49.10983 E, 80 m, tropical dry forest, sifted litter (leaf mold, rotten wood), collection code BLF02858, 10.-16.II.2001 (B.L. Fisher, C. Griswold et al.) (CASC: CASENT0445167). Paratypes, 15 workers with same data as holotype (BMNH: CASENT0443679; CASC: CASENT0439463; CASENT0443689; CASENT0445147; CASENT0445161; CASENT0445174; CASENT0448424; CASENT0448440; CASENT0448557; CASENT0448579; CASENT0448643; CASENT0448665; MCZ: CASENT0443659; MHNG: CASENT0448417; NHMB: CASENT0448568).

Diagnosis

Tetramorium avaratra is easily recognisable within the T. jedi complex due to the following character combination: propodeal spines long (PSLI 27-34 without the Nosy Be specimens, and PSLI 27-37 with the Nosy Be material); petiolar node in dorsal view between 1.2 to 1.4 times wider than long (DPeI 126-137); dorsum of petiolar node only weakly rugose; base of first gastral tergite with superficial, fine, reticulate-punctate sculpture.

Description

HL 0.81-0.94 (0.88); HW 0.78-0.94 (0.87); SL 0.56-0.65 (0.60); EL 0.15-0.18 (0.17); PH 0.41-0.48 (0.45); PW 0.59-0.71 (0.65); WL 1.02-1.20 (1.12); PSL 0.24-0.33 (0.28); PTL 0.19-0.24 (0.22); PTH 0.33-0.40 (0.37); PTW 0.26-0.31 (0.29); PPL 0.23-0.30 (0.27); PPH 0.29-0.37 (0.34); PPW 0.30-0.38 (0.35); CI 97-101 (99); SI 66-72 (69); OI 18-20 (19); DMI 56-60 (57); LMI 38-41 (40); PSLI 27-37 (32); PeNI 43-46 (44); LPeI 54-66 (60); DPeI 126-137 (130); PpNI 50-56 (54); LPpI 74-85 (79); DPpI 124-137 (130); PPI 116-125 (120) (15 measured).

Head approximately as long as wide (CI 97-101); posterior head margin moderately concave. Anterior clypeal margin medially impressed. Frontal carinae strongly developed, diverging posteriorly, and ending at corners of posterior head margin. Antennal scrobes developed, moderately deep, and broad, without defined ventral margins. Antennal scapes very short, not reaching posterior head margin (SI 66-72). Eyes short (OI 18-20). Mesosomal outline in profile flat to weakly convex, strongly marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent; mesosoma comparatively stout and high (LMI 38-41). Propodeal spines long, spinose and acute (PSLI 27-37); propodeal lobes short, triangular, and moderately acute. Petiolar node in profile rectangular nodiform, approximately 1.5 to 1.8 times higher than long (LPeI 54-66), anterior and posterior faces approximately parallel, anterodorsal margin situated higher than posterodorsal, dorsum noticeably tapering backwards posteriorly; node in dorsal view approximately 1.2 to 1.4 times wider than long (DPeI 126-137). Postpetiole in profile rounded, approximately 1.2 to 1.4 times higher than long (LPpI 74-85); in dorsal view around 1.2 to 1.4 times wider than long (DPpI 124-137). Postpetiole in profile appearing less voluminous than petiolar node, in dorsal view 1.1 to 1.3 times wider than petiolar node (PPI 116-125). Mandibles finely to strongly striate; clypeus longitudinally rugose, with four to eight rugae, median ruga always present, well-developed and distinct, remaining rugae variably developed, usually weaker and sometimes irregularly arranged; cephalic dorsum between frontal carinae with 11 to 13 longitudinal rugae, most rugae running unbroken from posterior head margin to anterior clypeus, few rugae interrupted and none with cross-meshes; scrobal area mostly unsculptured; lateral and ventral head longitudinally rugose with very few cross-meshes. Mesosoma laterally and dorsally distinctly longitudinally rugose, lateral mesosoma sometimes weaker sculptured than dorsum. Forecoxae generally unsculptured, smooth, and shining, at most with superficial sculpture. Ground sculpture on head and mesosoma generally faint to absent. Waist segments weakly to moderately rugose, sculpture on petiolar node weaker than on postpetiole; both waist segments with conspicuous reticulate-punctate ground sculpture. First gastral tergite with superficial, fine reticulate-punctate sculpture, generally restricted to basal third of the tergite, in several specimens sculpture fairly reduced, but always present. All dorsal surfaces of body with abundant, long, and fine standing hairs. Anterior edges of antennal scapes with decumbent to suberect hairs. Body of uniform brown to dark brown colour, appendages often of lighter colour.

Notes

This new species is restricted in its distribution to several localities in the northern tip of Madagascar and Nosy Be. Interestingly, there is no material known from the area between the population on Nosy Be and the other localities from Andavakoera, Ankarana, Bekaraoka, Ampondrabe, and Analamerana. Tetramorium avaratra appears to have comparatively flexible habitat requirements, having been found in rainforests, tropical dry forests, and on tsingy. Also, T. avaratra appears to be a ground-active species sampled mainly from leaf litter, and seems restricted to low elevations of 30 to 425 m.

Tetramorium avaratra shows variation in two important morphological characters. First, the propodeal spines of T. avaratra are usually long, but relatively short for the T. tortuosum group, with a PSLI of 27-34 with a mean value of 31. The few specimens known from the island of Nosy Be, however, have significantly longer spines (PSLI 37-39). This is the only difference observed, and we consider it to be geographic variation since, as mentioned above, the Nosy Be population is fairly widely separated from the other T. avaratra populations. The second interesting character, which is variable, is the sculpture on the first gastral tergite. Generally, the reticulate-punctate ground sculpture is well-developed on the basal third and fairly conspicuous. Nevertheless, in some specimens from Ankarana and Andavakoera, this character is often weakly developed, but still always present and visible.

Within the complex, T. avaratra cannot be mistaken with T. jedi. The latter species has much more pronounced sculpture on the whole first gastral tergite, which is densely and strongly reticulate-punctate, while the sculpture in T. avaratra is only superficial, much less developed, and restricted to the basal third of the first gastral tergite. In addition, both differ in the shape of the petiolar node since it is distinctly longer than wide in T. jedi (DPeI 79-85), whereas it is wider than long in T. avaratra (DPeI 126-137). The third species in the T. jedi complex, T. pleganon, is morphologically much closer to T. avaratra. Tetramorium pleganon differs from T. avaratra in several aspects, although some are not obvious at first glance. The propodeal spines are generally much longer in T. pleganon (PSLI 37-44) than in T. avaratra (PSLI 27-34 without the Nosy Be specimens, PSLI 27-37 with the Nosy Be material). Additionally, the petiolar node dorsum is wider and higher in T. avaratra (DPeI 126-137; LPeI 54-66) than in T. pleganon (DPeI 111-118; LPeI 63-73. Apart from these differences, both species differ also in the development of sculpture on the waist segments and the first gastral tergite, which is generally less well-developed in T. avaratra than in T. pleganon. This is especially visible on the dorsum of the petiolar node, which is always strongly rugose in T. pleganon but much less rugose in T. avaratra, where it is partly smooth. The distribution ranges of both species overlap. Indeed, T. pleganon and T. avaratra are found in sympatry in Ankarana while retaining their species-characteristics, providing additional evidence for their heterospecificity.

As already mentioned above, it is possible that T. avaratra and T. pleganon are not members of the T. tortuosum group. The petiolar nodes of both are wider than long in dorsal view (DPeI 111-137) while all other T. tortuosum group species have petiolar node shapes that range from distinctly longer than wide to weakly wider than long (DPeI 72-114, usually below 100). Also, the general morphology of T. avaratra and T. pleganon, in particular the shape of the petiolar node and strong margination, is very close to some species from the T. dysalum species group, especially T. dysalum. However, no member of the T. dysalum group has a sculptured first gastral tergite, which clearly distinguishes T. avaratra and T. pleganon from that group despite the strong general similarity with T. dysalum. The latter species also has completely unsculptured mandibles, whereas the mandibles of T. avaratra and T. pleganon are always sculptured, even though sometimes only finely so. At present, we consider these two species best placed within the T. tortuosum group, but cannot discount that they might be more closely related to another species group or represent a lineage parallel to other Malagasy species groups.

Etymology

The species epithet is an arbitrary combination of letters.

Material examined

MADAGASCAR: Antsiranana, Forêt d'Ampondrabe, 26.3km 10° NNE Daraina, 12.97 S, 49.7 E, 175 m, tropical dry forest, 10.XII.2003 (B.L. Fisher); Antsiranana, Rés. Analamerana, 28.4 km 99° Anivorano-Nord, 12.74667 S, 49.49483 E, 60 m, tropical dry forest, 5.XII.2004 (B.L. Fisher); Antsiranana, Forêt d' Andavakoera, 21.4 km 75° ENE Ambilobe, 13.11833 S, 49.23 E, 425 m, rainforest 15.XII.2003 (B.L. Fisher); Antsiranana, Réserve Spéciale de l'Ankarana, 22.9 km 224° SW Anivorano Nord, 12.90889 S, 49.10983 E, 80 m, tropical dry forest, 10.-16.II.2001 (B.L. Fisher, C. Griswold et al.); Antsiranana, Réserve Spéciale de l'Ankarana, 13.6 km 192° SSW Anivorano Nord, 12.86361 S, 49.22583 E, 210 m, tropical dry forest, 16.-21.II.2001 (B.L. Fisher, C. Griswold et al.); Antsiranana, Forêt de Bekaraoka, 6.8 km 60° ENE Daraina, 13.16667 S, 49.71 E, 150 m, tropical dry forest, 7.XII.2003 (B.L. Fisher); Antsiranana, Nosy Be, Réserve Naturelle Intégrale de Lokobe, 6.3 km 112° ESE Hellville, 13.41933 S, 48.33117 E, 30 m, rainforest, 19.-24.III.2001 (B.L. Fisher, C. Griswold et al.).