Tetramorium macki, Garcia & Fisher, 2012

Garcia, Francisco Hita & Fisher, Brian L., 2012, The ant genus Tetramorium Mayr (Hymenoptera: Formicidae) in the Malagasy region — taxonomy of the T. bessonii, T. bonibony, T. dysalum, T. marginatum, T. tsingy, and T. weitzeckeri species groups, Zootaxa 3365, pp. 1-123 : 68-70

Tetramorium macki sp. n.

(figs 76, 101, 102, 103)

Holotype worker, MADAGASCAR, Toamasina, F.C. Sandranantitra, 18.04833 S, 49.09167 E, 450 m, rainforest, sifted litter (leaf mold, rotten wood), collection code HJR102, 21.–24.I.1999 (H.J. Ratsirarson) ( CASC: CASENT0189093 ) . Paratypes, seven workers from Toamasina, F.C. Andriantantely, 18.695 S, 48.81333 E, 530 m, rainforest, sifted litter, collection code HJR121, 4.–7.XII.1998 (H.J. Ratsirarson) ( CASC: CASENT0217710 , CASENT0217711 , CASENT0218032 , CASENT0247151 ) .

Diagnosis

Tetramorium macki can be recognised easily within the T. steinheili group due to the following character combination: short antennal scapes (SI 70–74); comparatively short propodeal spines (PSLI 21–24); weakly cuneiform petiolar node shape with the anterodorsal angle situated higher than the posterodorsal, so that the dorsum tapers backwards posteriorly; mesosomal dorsum with longitudinally rugose sculpture; completely unsculptured waist segments; yellowish colouration.

Description

HL 0.49–0.58 (0.53); HW 0.45–0.54 (0.48); SL 0.32–0.39 (0.35); EL 0.09–0.12 (0.10); PH 0.25–0.30 (0.27); PW 0.34–0.43 (0.38); WL 0.57–0.71 (0.62); PSL 0.11–0.14 (0.12); PTL 0.11–0.13 (0.12); PTH 0.20–0.23 (0.21); PTW 0.16–0.19 (0.17); PPL 0.14–0.16 (0.15); PPH 0.19–0.21 (0.20); PPW 0.21–0.24 (0.22); CI 90–94 (92); SI 70–74 (72); OI 20–23 (21); DMI 58–63 (61); LMI 42–45 (43); PSLI 21–24 (23); PeNI 43–49 (46); LPeI 51–59 (55); DPeI 142–156 (150); PpNI 52–62 (58); LPpI 71–76 (73); DPpI 147–157 (151); PPI 122–132 (127) (13 measured).

Head distinctly longer than wide (CI 90–94). Anterior clypeal margin medially impressed. Frontal carinae moderately developed and fine, ending between posterior eye margin and posterior head margin. Antennal scrobes faint. Antennal scapes short, ending between posterior eye margin and posterior head margin (SI 70–74). Eyes small to moderate (OI 20–23). Mesosomal outline in profile weakly convex, moderately marginate from lateral to dorsal mesosoma, promesonotal suture and metanotal groove absent; mesosoma in profile comparatively stout and compact (LMI 42–45). Propodeal spines short to moderate, elongate-triangular and acute (PSLI 21–24). Propodeal lobes short and triangular. Petiolar node in profile high nodiform to cuneiform, approximately 1.7 to 2 times higher than long (LPeI 51–59), anterior and posterior faces not parallel, anterodorsal margin situated much higher than posterodorsal margin, dorsum distinctly tapering backwards posteriorly; node in dorsal view approximately 1.5 times wider than long (DPeI 142–156). Postpetiole in profile rounded, approximately 1.3 to 1.4 times higher than long (LPpI 71–76), in dorsal view approximately 1.5 times wider than long (DPpI 147–157). Postpetiole in profile approximately as voluminous as petiolar node, in dorsal view approximately 1.2 to 1.3 times wider than petiolar node (PPI 122–132). Mandibles finely striate but generally fairly shiny; clypeus with three to five longitudinal rugae or rugulae; cephalic dorsum between frontal carinae with six to eight longitudinal rugae, rugae running almost unbroken to posterior head margin, cross-meshes rare; lateral head weakly sculptured, anteriorly with irregular longitudinal rugulae mostly. Ground sculpture generally faint. Lateropronotum with weak sculpture only, remainder of lateral mesosoma with mainly longitudinally arranged, irregular rugae or rugulae. Both waist segments and gaster unsculptured, smooth and shining. All dorsal surfaces of body with long, fine, erect to suberect pilosity. Head, mesosoma, waist segments, and gaster of yellowish to light brownish colour; appendages of weakly lighter colour.

Notes

At present, the new species is only known to occur in Andriantantely, Betampona, Didy, and Sandranantitra. All four localities are comparatively close to each other geographically, and represent lowland rainforests lying at altitudes between 450 m to 960 m. On the basis of the available collection label data, T. macki appears to live in leaf litter.

Tetramorium macki can be straightforwardly identified within the T. dysalum group due to its combination of short propodeal spines (PSLI 21–24), weakly cuneiform petiolar node, and yellow colouration. The other two species with short propodeal spines/teeth, T. orc and T. robitika , are not likely to be confused with T. macki . Tetramorium robitika has a high nodiform petiolar node with anterodorsal and posterodorsal margins at about the same height while T. macki has a cuneiform node with the dorsum tapering backwards posteriorly. Also, T. orc with its shorter antennal scapes (SI 68–69) and dark to very dark brown colouration differs strikingly from T. macki with its longer antennal scapes (SI 70–74) and yellowish colouration.

As noted above, within the T. dysalum group T. macki is fairly easy to differentiate from the remaining species. However, T. macki has a general gestalt that is comparatively close to the one seen in some members of the T. ranarum group ( T. degener Santschi and few morphologically similar undescribed species), and without close examination they could be confused with each other. All are relatively small, yellowish species with a petiolar node which is higher and wider than it is long, and comparatively small propodeal spines. Yet these T. ranarum group members either have propodeal lobes of approximately the same length and shape as the propodeal spines or a petiolar node with distinct sculpture, whereas T. macki possesses propodeal spines of short to moderate length that are much longer than the propodeal lobes, and a completely unsculptured petiolar node. These ants also differ in gastral pilosity. In T. macki the gastral pilosity is mainly suberect to erect with few subdecumbent to decumbent hairs while the gastral pilosity of T. degener and allies is mainly appressed to subdecumbent with few erect hairs. This character, in combination with the unsculptured, higher and wider petiolar node, justifies the placement of T. macki within the T. dysalum group. Nevertheless, these ants represent a good example of seemingly convergent evolution. Despite belonging to different groups, T. macki and T. degener and allies all are comparatively small species with reduced characters in comparison to their respective group members, and their general habitus might be misleading at first glance. Another difference is their preferred habitat, because T. macki , like most other T. dysalum members, is only found in humid rainforests, whereas T. degener and allies prefer much more arid habitats, such as spiny forests or thickets, woodlands, tropical dry forests, or anthropogenically modified habitats.

Etymology

The new species is named in honor of Dawn M. Mack for her support to discover and identify life on earth.

Material examined

MADAGASCAR: Toamasina, F.C. Andriantantely, 18.695 S, 48.81333 E, 530 m, rainforest, 4.–7.XII.1998 (H.J. Ratsirarson); Toamasina, F.C. Didy, 18.19833 S, 48.57833 E, 960 m, rainforest, 16.–23.XII.1998 (H.J. Ratsirarson); Toamasina, F.C. Sandranantitra, 18.04833 S, 49.09167 E, 450 m, rainforest, 21.–24.I.1999 (H.J. Ratsirarson); Toamasina, Réserve Nationale Intégrale Betampona, Betampona 35.1 km NW Toamasina, 17.91801 S, 49.20074 E, 500 m, rainforest, 16.XII.2007 (B.L. Fisher et al.).