Tetramorium orientale Forel, 1895a

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 : 22-24

Tetramorium orientale Forel, 1895a stat. n.

(figs 7, 20, 21, 22)

Tetramorium (Xiphomyrmex) bessonii var. orientale Forel, 1895a:247 . Holotype worker, MADAGASCAR, Fianarantsoa, Imerina (Sikora) (MHNG: CASENT0101744) [examined]. [Synonymy with T. bessonii by Bolton, 1979:141].

Diagnosis

Tetramorium orientale is easily recognisable within its species group due to the character combination of: welldeveloped, conspicuous promesonotal suture; high nodiform petiolar node in profile with approximately parallel anterior and posterior faces, anterodorsal and posterodorsal angles at about same height, dorsum not tapering backwards posteriorly; absence of standing hairs on waist segments and first gastral tergite, and very short, appressed pubescence on first gastral tergite.

Description

HL 0.82; HW 0.84; SL 0.62; EL 0.18; PH 0.48; PW 0.63; WL 1.06; PSL 0.28; PTL 0.19; PTH 0.34; PTW 0.30; PPL 0.25; PPH 0.35; PPW 0.39; CI 102; SI 74; OI 21; DMI 59; LMI 45; PSLI 34; PeNI 47; LPeI 57; DPeI 155; PpNI 62; LPpI 71; DPpI 156; PPI 132 (one measured).

Head wider than long (CI 102). Anterior clypeal margin with distinct median impression. Frontal carinae well developed, ending shortly between posterior eye margin and posterior head margin. Antennal scrobes faint to absent, posterior and ventral margins not differentiated. Antennal scapes short, not reaching posterior head margin (SI 74). Eyes small to moderate (OI 21). Mesosomal outline in profile convex, dorsally transversely rounded, weakly marginate from lateral to dorsal mesosoma, promesonotal suture present, metanotal groove weakly developed; mesosoma comparatively stout and high (LMI 45). Propodeal spines long, spinose, and acute (PSLI 34). Propodeal lobes very small and broadly triangular. Petiolar node high nodiform, anterior and posterior faces approximately parallel, anterodorsal and posterodorsal angles at about same height, dorsum not tapering backwards posteriorly; node in dorsal view not strongly transverse, approximately 1.5 to 1.6 times wider than long (DPeI 155), in lateral view 1.8 times higher than long (LPeI 57). Postpetiole in profile rounded and weakly anteroposteriorly compressed, 1.4 times higher than long (LPpI 71), in dorsal view approximately approximately 1.5 to 1.6 times wider than long (DPpI 156). Postpetiole in profile approximately as voluminous as petiolar node, in dorsal view 1.3 times wider than petiolar node (PPI 132). Mandibles striate; clypeus with strong median longitudinal rugae and one weaker ruga at each side; cephalic dorsum between frontal carinae with one well-developed longitudinal median ruga and traces of short rugulae laterally, median ruga of same length as frontal carinae and diverging approximately at eye level into two rugae running to posterior clypeal margin; scrobal area unsculptured, lateral and ventral head anteriorly with irregular longitudinal rugulae, posteriorly with almost unsculptured; ground sculpture on head faint to absent. Mesosoma, waist segments, and gaster unsculptured, smooth, and shining. Head with several pairs of standing hairs, mesosoma with only one pair on pronotal dorsum, waist segments and first gastral tergite without any pilosity; all dorsal surfaces of body with widely-spaced, very short, and appressed pubescence. Body uniformly brown.

Notes

This species is only known from the type locality. Unfortunately, the information from the type label data is very limited. The locality given is "Imerina", which can mean a wide area on the Central Plateau of Madagascar. This very broad geographical reference does not allow an exact determination of the type locality.

Tetramorium orientale was originally described as subspecies of T. bessonii ( Forel, 1895a) , and later synonymised under the same species ( Bolton, 1979). This synonymisation is understandable considering the geographically limited material available at the time. Bolton (1979) only revised T. bessonii since none of the other species group members were known, and the only specimen of T. orientale was most likely a rare variation of T. bessonii . However, our study shows that T. orientale is not conspecific with T. bessonii since both differ in several aspects that provide sufficient evidence to raise T. orientale to species status. The petiolar node shape, which is strongly anteroposteriorly compressed with the anterodorsal margin situated higher than the posterodorsal in T. bessonii , is less compressed, more high nodiform with antero- and posterodorsal margins at about the same height in T. orientale . Furthermore, the cephalic sculpture consisting of several rugae between the frontal carinae always present in T. bessonii is reduced to a single median ruga in T. orientale . Another character that separates both species is head shape. The head of T. bessonii is always distinctly longer than wide (CI 92–96) while it is wider than long in T. orientale (CI 102).

Within the species group, T. orientale is morphologically closer to T. malagasy and T. ryanphelanae . All three have the high nodiform petiolar node in profile in common, which differs from the strongly anteroposteriorly compressed node seen in T. artemis , T. bessonii , and T. wardi . However, T. orientale displays much shorter pubescence and a lack of standing hairs on waist segments and first gastral tergite in comparison to T. ryanphelanae , making these species unlikely to be confused. Tetramorium malagasy , however, is very similar to T. orientale , and it is possible that both are indeed the same species. The only character separating them is the welldeveloped and conspicuous promesonotal suture, which is present in T. orientale , and the lack of it in T. malagasy . A single morphological character might seem to be a weak argument, but our decision is based on the examination of a large number of T. malagasy specimens from numerous localities throughout Madagascar, and, as pointed out above, not a single one showed the noticeable promesonotal suture seen in T. orientale . Unfortunately, the unknown type locality of T. orientale makes it difficult to obtain fresh specimens. Furthermore, since it is only known from the holotype, which is more than 100 years old, it is not possible to recover genetic material that could be used to test this ant’s conspecificity with T. malagasy . For all of these reasons, we consider both to be distinct species, although we cannot rule out the possibility that the single specimen of T. orientale is an aberrant form of T. malagasy .