Tetramorium plesiarum 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 : 38-41

Tetramorium plesiarum Bolton Figs 10C, 11B, 13B, 14A, 19, 62

Tetramorium plesiarum Bolton, 1979: 150.

Type material.

Holotype, pinned worker, MADAGASCAR, Causse de Kelifely, 17.30306°S, 45.73444°E, forest humus and litter, dry forest, 20.-30.XI.1974 (A. Peyrieras) (MCZ: MCZ_Holotype_32372) [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 Kelifely limestone plateau and should be considered an approximation but not the exact position of the type locality.]

Non-type material.

MADAGASCAR: Mahajanga, Reserve Forestiere Beanka, 50.7 km E Maintirano, 17.8802°S, 44.4688°E, 140 m, tropical dry forest on tsingy, 29.X.-1.XI.2009 (B.L. Fisher et al.); Mahajanga, Parc National de Namoroka, 9.8 km 300° WNW Vilanandro, 16.4667°S, 45.35°E, 140 m, tropical dry forest, 4.-8.XI.2002 (B.L. Fisher et al.); Mahajanga, Parc National de Namoroka, 17.8 km 329° WNW Vilanandro, 16.3767°S, 45.3267°E, 100 m, tropical dry forest, 8.-12.XI.2002 (B.L. Fisher et al.); Mahajanga, Parc National de Namoroka, 16.9 km 317° NW Vilanandro, 16.4067°S, 45.31°E, 100 m, tropical dry forest, 12.-16.XI.2002 (B.L. Fisher et al.); Mahajanga, Parc National Tsingy de Bemaraha, 10.6 km ESE 123° Antsalova, 18.7094°S, 44.7182°E, 150 m, tropical dry forest on tsingy, 16.-20.XI.2001 (B.L. Fisher et al.); Toliara, Parc National d’Andohahela, Forêt de Manantalinjo, 33.6 km 63° ENE Amboasary, 7.6 km 99° E Hazofotsy, 24.8169°S, 46.61°E, 150 m, spiny forest/thicket, 12.-16.I.2002 (B.L. Fisher et al.); Toliara, Parc National d’Andohahela, Forêt d’Ambohibory, 1.7 km 61° ENE Tsimelahy, 36.1 km 308° NW Tolagnaro, 24.93°S, 46.6455°E, 300 m, tropical dry forest, 16.-20.I.2002 (B.L. Fisher et al.); Toliara, Andohahela National Park, Tsimelahy–Parcel II, 24.9368°S, 46.6267°E, 180 m, transition forest, 5.-15.II.2003 (M.E. Irwin et al.); Toliara, Makay Mts., 21.2184°S, 45.3106°E, 510 m, gallery forest on sandy soil, 24.-27.XI.2010 (B.L. Fisher et al.); Toliara, Makay Mts., 21.2176°S, 45.3392°E, 500 m, gallery forest on sandy soil, 28.XI.2010 (B.L. Fisher et al.); Toliara, Makay Mts., 21.3136°S, 45.1478°E, 525 m, gallery forest on sandy soil, 6.XII.2010 (B.L. Fisher et al.); Toliara, Vohibasia Forest, 59 km NE Sakaraha, 22.4667°S, 44.85°E, 780 m, tropical dry forest, 13.I.1996 (B.L. Fisher); Toliara, Parc National de Zombitse, 19.8 km 84° E Sakaraha, 22.8433°S, 44.71°E, 770 m, tropical dry forest, 5.-9.II.2003 (B.L. Fisher et al.).

Diagnosis.

The following character set separates Tetramorium plesiarum from the remainder of the species group: smaller species (HW 0.80-1.00; WL 0.92-1.15); eyes of moderate size (OI 21-23); petiolar node high nodiform, not massively enlarged, anterodorsal margin protruding anteriorly and slightly more marginate than posterodorsal margin; petiolar node in profile relatively high and thin, between 1.6 to 1.8 times higher than long (LPeI 56-63), in dorsal view between 1.3 to 1.4 times wider than long (DPeI 131-137); gaster never extremely enlarged and swollen; head without strongly developed and conspicuous reticulate-punctate ground sculpture; mesopleuron and lateral propodeum with moderate punctate ground sculpture; first gastral tergite without strong reticulate-rugose sculpture, usually completely unsculptured, but if sculpture present, then relatively weak and restricted to base of tergite; pilosity on first gastral tergite mostly erect.

Worker measurements

(N=12). HL 0.66-0.75 (0.73); HW 0.67-0.76 (0.72); SL 0.45-0.49 (0.47); EL 0.15-0.17 (0.15); PH 0.33-0.44 (0.36); PW 0.50-0.57 (0.53); WL 0.81-0.92 (0.85); PSL 0.16-0.21 (0.18); PTL 0.18-0.22 (0.19); PTH 0.31-0.35 (0.33); PTW 0.23-0.29 (0.26); PPL 0.22-0.26 (0.24); PPH 0.29-0.33 (0.31); PPW 0.32-0.40 (0.35); CI 97-102 (99); SI 64-69 (66); OI 21-23 (22); DMI 60-65 (63); LMI 41-47 (43); PSLI 23-28 (25); PeNI 45-51 (49); LPeI 56-63 (59); DPeI 131-137 (133); PpNI 63-70 (66); LPpI 73-79 (76); DPpI 140-157 (149); PPI 129-143 (136).

Worker description.

Head more or less as long as broad (CI 97-102); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae strongly developed and forming dorsal margin of very well-developed antennal scrobes, scrobes moderately to very deep and with clearly defined margins all around; median scrobal carina very well developed and distinctly surpassing posterior eye level, usually ending halfway between posterior eye margin and posterior scrobe margin, often approaching posterior scrobe margin. Antennal scapes short, not reaching posterior head margin (SI 64-69). Eyes small to moderate (OI 21-23). Mesosomal outline in profile weakly to moderately convex, rounded and high (LMI 41-47), moderately marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent. Propodeal spines elongate-triangular to spinose, moderately long to long, and acute (PSLI 23-28), spines always with broad base and acute tip; propodeal lobes well developed, triangular to elongate-triangular, and acute, always much shorter than propodeal spines. Petiolar node in profile high nodiform, between 1.6 to 1.8 times higher than long (LPeI 56-63), anterodorsal margin situated higher and more angled than posterodorsal, more rounded margin, petiolar dorsum weakly to moderately tapering backwards posteriorly, anterodorsal margin slightly protruding anteriorly, anterior and posterior faces approximately parallel; node in dorsal view between 1.3 to 1.4 times wider than long (DPeI 131-137), pronotum between 1.9 to 2.2 times wider than petiolar node (PeNI 45-51). Postpetiole in profile subglobular, approximately 1.3 to 1.4 times higher than long (LPpI 73-79); in dorsal view around 1.4 to 1.6 times wider than long (DPpI 140-157), in dorsal view pronotum between 1.4 to 1.6 times wider than postpetiole (PpNI 63-70). Postpetiole in profile appearing slightly less voluminous than petiolar node, postpetiole in dorsal view about 1.3 to 1.4 times wider than petiolar node (PPI 129-143). Mandibles unsculptured, smooth, and shining; clypeus longitudinally rugose, with three to five distinct rugae, median ruga better developed than remainder, rugae without cross-meshes; cephalic dorsum between frontal carinae with ten to twelve longitudinal rugae, rugae running from posterior clypeal margin to posterior head margin, often interrupted or with cross-meshes, especially posteriorly; scrobal area mostly unsculptured, relatively smooth and shiny; lateral head longitudinally rugose to reticulate-rugose. Ground sculpture on head usually present but weak. Mesosoma laterally irregularly longitudinally rugose, usually with moderate punctate ground sculpture on mesopleuron and propodeum, dorsal mesosoma longitudinally rugose without any distinct ground sculpture, spaces between rugae smooth and shining. Forecoxae unsculptured, smooth, and shining. Sides of petiolar node and postpetiole with conspicuous, moderate reticulate-punctate ground sculpture, both nodes appearing relatively matte; petiolar node and postpetiole dorsally weakly rugulose/rugose, but mostly unsculptured, and appearing smooth and shining. Gaster usually unsculptured, smooth and shining, sometimes base of first gastral tergite with traces of punctate ground sculpture. Whole body with very abundant, dense, moderately long, and fine standing hairs; first gastral tergite with abundant, long, erect hairs and much scarcer, shorter, decumbent to subdecumbent hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with decumbent to suberect hairs. Body of uniform brown, appendages often lighter.

Distribution and biology.

Despite being known only from seven localities and fewer than 20 specimens, Tetramorium plesiarum has a comparatively large distribution range (Fig. 62). However, the populations appear to be relatively disjunctive. The species is known from Andohahela in the southeast of Madagascar and from six additional, more or less scattered localities in the western part of the island ranging from Zombitse and Vohibatsia north through the Makay Mountains, Tsingy de Bemaraha, and Beanka to the Kelifely plateau and Namoroka. The small number of specimens suggests that Tetramorium plesiarum is much less common than the sympatric Tetramorium bressleri , which shares much of the distribution range, but is known from many more localities and hundreds of specimens. The rarity of Tetramorium plesiarum might well explain the disjunctive distribution. Unfortunately, there is no “fresh” material available from the type locality since the holotype remains the only known specimen from the Kelifely plateau. All localities are tropical dry forests, tropical dry forests on tsingy, or gallery forests ranging from 100 to 780 m elevation. Like the other group members Tetramorium plesiarum was mostly collected by pitfall trapping and litter sifting suggesting a ground-active lifestyle.

Discussion.

Tetramorium plesiarum lacks strong specialisations, such as the strongly sculptured and enlarged gaster of Tetramorium gollum , or the massively developed petiolar node of Tetramorium hobbit . Furthermore, Tetramorium mars has a lower and wider petiolar node (LPeI 69-76; DPeI 108-123) compared to Tetramorium plesiarum (LPeI 56-63; DPeI 131-137). The latter also has much less sculpture on the dorsum of the petiolar node. Within the species group Tetramorium plesiarum is morphologically most similar to Tetramorium bressleri , and as mentioned in the description of the latter, we have treated them as conspecific through most of the revision The most noticeable difference is certainly body size since Tetramorium bressleri (HW 0.80-1.00; WL 0.92-1.15) is much larger than Tetramorium plesiarum (HW 0.80-1.00; WL 0.92-1.15). As noted above, there is some slight overlap caused by one large specimen of Tetramorium plesiarum and very few small specimens of Tetramorium bressleri , but in the main they fit their respective size ranges. Not considering body size, they also differ in eye size and sculpture on mesosoma and waist segments. The eyes of Tetramorium plesiarum (OI 21-23) are larger than in Tetramorium bressleri (OI 18-19). The mesopleuron and lateral propodeum of Tetramorium bressleri is usually mostly unsculptured and relatively smooth and shining, whereas this area is longitudinally rugose with reticulate-punctate ground sculpture in Tetramorium plesiarum . Almost the same pattern is seen in the sculpture on the lateral petiolar node as it is significantly more reticulate-punctate and matte in Tetramorium plesiarum than in Tetramorium bressleri , in which the weak reticulate-punctate ground sculpture appears faintly matte but still relatively smooth and shiny. The sculpture on the sides of the petiolar node varies, too, since it is much more reticulate-punctate and matte in Tetramorium plesiarum than in Tetramorium bressleri , in which the weak reticulate-punctate ground sculpture looks faintly matte but still relatively smooth and shiny. The shape of the petiolar node in profile is an additional useful character. Finally, in Tetramorium plesiarum the anterodorsal margin of the petiolar node protrudes anteriorly and is slightly more marginate than the more rounded posterodorsal margin, contrasting with the shape observed in Tetramorium bressleri , in which both margins are usually equally marginate and the anterodorsal margin does not protrude anteriorly at all.