Tetramorium pleganon Bolton,

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 : 53-56

Tetramorium pleganon Bolton, 1979

(Figs. 48, 108, 109, 110, 142)

Tetramorium pleganon Bolton, 1979:146. Holotype worker, MADAGASCAR, Antsiranana, 84 km SW Sambava on road to Andapa, 70-160 m, degraded forest, strays on path, AB 43, 17.II.1977 (W.L. & D.E. Brown) (MCZ: CASENT0280587) [examined]. Paratypes, three workers with same data as holotype (BMNH: CASENT0102399; MCZ: CASENT0280588) [examined].

Diagnosis

Tetramorium pleganon is easily recognisable within the T. tortuosum group in the Malagasy region due to the character combination of: propodeal spines long to very long (PSLI 37-44); petiolar node wider than long (DPeI 111-118); dorsum of petiolar node strongly rugose; first gastral tergite with superficial, fine, reticulate-punctate sculpture, ranging from basal third to more than half of tergite.

Description

HL 0.87-1.05 (0.93); HW 0.85-1.02 (0.91); SL 0.61-0.73 (0.66); EL 0.18-0.23 (0.19); PH 0.43-0.56 (0.48); PW 0.59-0.79 (0.69); WL 1.07-1.31 (1.17); PSL 0.32-0.43 (0.37); PTL 0.22-0.31 (0.25); PTH 0.34-0.44 (0.37); PTW 0.26-0.34 (0.29); PPL 0.27-0.34 (0.29); PPH 0.31-0.43 (0.35); PPW 0.34-0.43 (0.38); CI 96-99 (97); SI 71-74 (73); OI 20-23 (21); DMI 52-61 (59); LMI 38-43 (41); PSLI 37-44 (39); PeNI 40-44 (42); LPeI 63-73 (67); DPeI 111-118 (115); PpNI 52-61 (55); LPpI 80-89 (83); DPpI 122-137 (129); PPI 126-138 (130) (14 measured).

Head longer than wide (CI 96-99); posterior head margin moderately concave. Anterior clypeal margin medially impressed, often weakly so. Frontal carinae st rongly developed, diverging posteriorly, and ending at corners of posterior head margin. Antennal scrobes developed, shallow to moderately deep, and broad, without defined posterior and ventral margins. Antennal scapes short, not reaching posterior head margin (SI 71-74). Eyes small to moderate in size (OI 20-23). Mesosomal outline in profile weakly convex, moderately marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent; mesosoma comparatively stout and high (LMI 38-43). Propodeal spines very long, spinose and acute (PSLI 37-44); propodeal lobes short, triangular, and acute. Petiolar node in profile rectangular nodiform, approximately 1.1 to 1.2 times higher than long (LPeI 63-73), anterior and posterior faces approximately parallel, anterodorsal margin situated higher than posterodorsal, dorsum weakly tapering backwards posteriorly; node in dorsal view approximately 1.1 to 1.2 times wider than long (DPeI 111-118). Postpetiole in profile rounded, approximately 1.1 to 1.3 times higher than long (LPpI 80-89); in dorsa l view around 1.2 to 1.4 times wider than long (DPpI 122-137). Postpetiole in profile approximately as voluminous as petiolar node, in dorsal view 1.2 to 1.4 times wider than petiolar node (PPI 126-138). Mandibles generall y finely to strongly striate; clypeus longitudinally rugose, with four to nine rugae, median ruga always present and distinct, remaining rugae variably developed, usually weaker; cephalic dorsum between frontal carinae with 11 to 14 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, very rarely with cross-meshes. Ground sculpture on head generally feeble. Mesosoma laterally and dorsally distinctly longitudinally rugose, lateral mesosoma sometimes weaker sculptured than dorsum. Forecoxae generally unsculptured, smooth, and shining, sometimes with superficial scul pture. Ground sculpture on mesosoma generally faint to absent. Waist segments strongly rugose dorsally, laterally rugose sculpture much weaker; both waist segments with very conspicuous reticulate-punctate ground sculpture. First gastral tergite with fine, dense, reticulate-punctate ground sculpture, ranging from basal third to mo re than half of tergite. All dorsal surfaces of body with abundant, long, and fine standing hairs; first gast ral tergite with mix of moderately long appressed to decumbent hairs and more abundant and longer suberect to erect hairs. Anterior edges of antennal scapes with decumbent to suberect hairs. Body a uniform very dark brown to black colour, appendages often lighter in colour.

Notes

Tetramorium pleganon possesses a comparatively wide distribution in Madagascar since it is found in many localities from Zombitse and Kalambatrita in the south up to Ambato and Antsahabe in the north. It appears to be comparatively flexible in its habitat preferences. Most of the localities where it was encountered consisted of rainforest, montane rainforest, or tropical dry forest, but the number of specimens collected in these habitats was comparatively low. In contrast, the largest number of examined specimens were sampled in Uapaca woodland, savannah grassland, and degraded forests, indicating that T. pleganon might be more successful in disturbed and open habitats than in dense forests.

In Bolton's (1979) revision T. pleganon was easily diagnosable and recognisable from all other Malagasy Tetramorium due to its 11-segmented antennae and the sculptured first gastral tergite. However, our ongoing revision has revealed several species with 11-segmented antennae and sculpture on the first gastral tergite, indicating this character combination is more common than previously thought, and is certainly not unique to T. pleganon. Nevertheless, within the T. tortuosum group there are different types of sculpture observable on the first gastral tergite, and the reticulate-punctate ground sculpture seen in T. pleganon places it well within the T. jedi complex. Within this complex, T. pleganon is unlikely to be misidentified with T. jedi since the latter species has a completely sculptured tergite with very strongly developed and conspicuous reticulate-punctate sculpture. In T. pleganon the sculpture is well-developed, too, but much more superficial, and does not cover the whole tergite. In addition, the petiolar node of T. pleganon is distinctly wider than long (DPeI 111-188), which contrasts with the clearly longer than wide node of T. jedi (DPeI 79-85). Tetramorium avaratra, the third species of the complex, is morphologically much closer to T. pleganon, but differs in propodeal spine length, petiolar node shape, and general development of sculpture on waist segments and gaster. Tetramorium avaratra has generally much shorter propodeal spines (PSLI 27-34 without the Nosy Be specimens, PSLI 27-37 with the Nosy Be material) than T. pleganon (PSLI 37-44). Also, the petiolar node is higher and wider in T. avaratra (LPeI 54-66; DPeI 126-137) than in T. pleganon (LPeI 63-73; DPeI 111-118), and the latter species has much better developed sculpture on the waist segments and the first gastral tergite. As noted in the description of T. avaratra, both species overlap in their distribution, and are found living in sympatry in Ankarana. However, both species display their species-characteristics in this locality, and can be well separated from each other by the diagnostics provided above.

Despite this wide distribution range and relative flexibility in habitat preference, T. pleganon is morphologically very stable throughout its range with very little variation in morphometry, shape, or colour. The morphological similarities with T. dysalum, as well as the potentially erroneous placement of T. avaratra and T. pleganon within the T. tortuosum species group, are discussed in detail in the description of T. avaratra.

Material examined

MADAGASCAR: Antananarivo, Réserve Spéciale d'Ambohitantely, Forêt d Ambohitantely, 20.9 km 72° NE d Ankazobe, 18.22528 S, 47.28683 E, 1410 m, montane rainforest, 17.-22.IV.2001 (B.L. Fisher, C. Griswold et al.); Antsiranana, Forêt Ambato, 26.6 km 33° Ambanja, 13.4645 S, 48.55167 E, 150 m, rainforest, 8.-10.XII.2004 (B.L. Fisher); Antsiranana, Ampasindava, Forêt d'Ambilanivy, 3.9 km 181° S Ambaliha, 13.79861 S, 48.16167 E, 600 m, rainforest, 4.-9.III.2001 (B.L. Fisher, C. Griswold et al.); Antsiranana, Andapa, 14° 40' S, 49° 39' E, 500 m, degraded forest, 26.I.1991 (G.D. Alpert); Antsiranana, 84 km SW Sambava on road to Andapa, 70-160 m, degraded forest, 17.II.1977 (W.L. & D.E. Brown); Antsiranana, Res. Ankarana, 12° 54' S, 49° 6' E, 100 m, tropical dry forest, 22.VIII.1992 (G.D. Alpert); Antsiranana, Forêt d' Antsahabe, 11.4 km 275° W Daraina, 13.21167 S, 49.55667 E, 550 m, tropical dry forest, 12.XII.2003 (B.L. Fisher); Antsiranana, R.S. Manongarivo, 10.8 km 229° SW Antanambao, 13.96167 S, 48.43333 E, 400 m, rainforest, 8.XI.1998 (B.L. Fisher); Antsiranana, R.S. Manongarivo, 12.8 km 228° SW Antanambao, 13.97667 S, 48.42333 E, 780 m, rainforest, 11.-17.X.1998 (B.L. Fisher); Antsiranana, Makirovana forest, 14.17066 S, 49.95409 E, 415 m, rainforest, 28.-29.IV.2011 (B.L. Fisher et al.); Fianarantsoa, Antapia II Non Protected Area, 26.47 km SW Ambositra, 20.71889 S, 47.0867 E, 1494 m, Uapaca woodland, 4.-6.II.2010 (A. Ravelomanana); Fianarantsoa, Antohatsahomby I Non Protected Area, 22.77 km NW Ambatofinandrahana, 20.55056 S, 46.58562 E, 1550 m, Uapaca woodland, 15.-17.III.2010 (A. Ravelomanana); Fianarantsoa, Mampiarika III Non Protected Area, 28.93 km SW Ambositra, 20.73583 S, 47.08399 E, 1487 m, Uapaca woodland, 1.-2.II.2010 (A. Ravelomanana); Fianarantsoa, Soanierenana I Non Protected Area, 25.33 km SW Ambositra, 20.72139 S, 47.10994 E, 1723 m, savannah grassland, 6.-8.II.2010 (A. Ravelomanana); Mahajanga, Parc National d'Ankarafantsika, Forêt de Tsimaloto, 18.3 km 46° NE de Tsaramandroso, 16.22806 S, 47.14361 E, 135 m, tropical dry forest, 2.-8.IV.2001 (B.L. Fisher, C. Griswold et al.); Mahajanga, Réserve d'Ankoririka, 10.6 km 13° NE de Tsaramandroso, 16.26722 S, 47.04861 E, 210 m, tropical dry forest, 9.-14.IV.2001 (B.L. Fisher, C. Griswold et al.); Toamasina, Ambatovy, 12.4 km NE Moramanga, 18.84773 S, 48.29568 E, 1000 m, montane rainforest, 5.-8.III.2007 (B.L. Fisher et al.); Toamasina, Manakambahiny, near Vavatenina Forest, 17.46667 S, 49.35 E, 9.II.1995 (A. Pauly); Toamasina, MoraranoChrome, 17.75 S, 47.98333 E, forest, 1.I.1992 (A. Pauly); Toamasina, S.F. Tampolo, 10 km NNE Fenoarivo Atn., 17.2825 S, 49.43 E, 10 m, littoral rainforest, 10.IV.1997 (B.L. Fisher); Toliara, Réserve Spéciale d'Ambohijanahary, Forêt d'Ankazotsihitafototra, 35.2 km 312° NW Ambaravaranala, 18.26667 S, 45.40667 E, 1050 m, montane rainforest, 13.-17.I.2003 (B.L. Fisher et al.); Toliara, Réserve Spéciale Kalambatritra, 23.4185 S, 46.4583 E, 1365 m, grassland, 8.II.2009 (B.L. Fisher et al.).