Tetramorium proximum

Tetramorium proximum appears to live in leaf litter.

Identification
A member of the Tetramorium cognatum species complex of the Tetramorium schaufussii species group. Hita Garcia and Fisher (2014) - Tetramorium proximum can be distinguished from the other members of the species complex on the basis of the following character combination: eyes relatively large (OI 24–28); antennal scapes short (SI 74–76); frontal carinae strongly developed, noticeably raised, and reaching or ending shortly before posterior head margin; propodeal spines short to medium-sized, elongate-triangular, and usually acute (PSLI 17–21); petiolar node high rounded nodiform, in profile around 1.7 to 1.9 times higher than long (LPeI 52–60), and in dorsal view around 1.3 to 1.5 times wider than long (DPpI 135–153); mesosoma with four to nine pairs of long, fine, standing hairs, usually five or six ranging from anterior pronotum to metanotal groove.

Tetramorium proximum is a very distinct species within the species complex. Due to its large body size (HW 0.65–0.81; WL 0.92–1.07) and strongly developed frontal carinae it cannot be mistaken for the five smaller species Tetramorium aspis, Tetramorium camelliae, Tetramorium cognatum, Tetramorium karthala, and Tetramorium rumo (HW 0.43–0.57; WL 0.56–0.81), all of which have weakly to moderately developed frontal carinae. Nor can T. proximum with its larger eyes (OI 24–28) and its long, standing pilosity on the dorsal mesosoma be confused with the smaller-eyed Tetramorium gladius (OI 19–20) or Tetramorium freya, which lacks any standing pilosity on the mesosoma. The remaining two species, Tetramorium myrmidon and Tetramorium tenuinode, are both morphologically close and relatively similar to Tetramorium proximum. The separation of these three requires more attention.

Tetramorium tenuinode, despite sharing a superficially similar habitus, differs from T. proximum in a number of characters, and co-occurs with the latter species throughout most of its distribution range while both species maintain their species-specific differences. The main diagnostic character is the pilosity on the dorsal mesosoma, which consists of two pairs of long, standing hairs (one on anterior pronotum and one on anterior mesonotum) in T. tenuinode, while in T. proximum there are usually five to six pairs (rarely four or more than six) from anterior pronotum to posterior mesonotum. Furthermore, T. proximum has significantly longer antennal scapes (SI 74–77) than T. tenuinode (SI 66–70), and is normally a darker colour. Also, T. tenuinode generally has a thinner petiolar node in lateral view that is around 1.8 to 2.2 times higher than long (LPeI 45–54), while the node of T. proximum is around 1.7 to 1.9 times higher than long (LPeI 52–60). There is some overlap in these morphometric ranges, but there is a strong general trend towards a much thinner node in T. tenuinode, which together with the other characters mentioned above works very well in distinguishing both species. The remaining species, T. myrmidon, might be confused with T. proximum since they share most morphological characters and their morphometric ranges overlap. Nevertheless, T. myrmidon is only found in Ambohijanahary where it co-occurs with T. proximum, and there they are both easily separable based on mesosomal pilosity (two pairs in T. myrmidon vs. five or six in T. proximum) and petiolar node height.

Tetramorium proximum is a relatively variable species with respect to certain characters. The greatest variation can be seen in gastral pubescence, which is always strongly appressed, but can vary from very short and scarce to relatively long and dense. Often this variation can be observed within the same locality or series, sometimes all specimens from one locality have short pubescence while populations from other localities have long pubescence. However, it seems that there is also a geographical component to this variation. The material from the southeast has predominantly long and dense pubescence, and the form with short pubescence is relatively rare, but still present. The material from central eastern Madagascar is a well-balanced mix of short and long pubescence. Interestingly, the material from the northeast, north, and the isolated forests in the west possesses almost exclusively short and scarce pubescence. Another, even though less variable character, is the shape of the petiolar node, which is high nodiform with a rounded dorsum, but can vary in height or thickness from population to population. Furthermore, some populations have fewer or more pairs of long, standing hairs on the mesosomal dorsum. The most common count is five to six pairs ranging throughout most of the distribution range, but in some localities one can see only four pairs while in others six to seven, and in a few series seven to eight pairs are common. The variation observed in T. proximum is not surprising, however, due to its wide distribution and commonness. Compared to other widely distributed and common Malagasy or Afrotropical Tetramorium species, this species actually shows much less variation.

Key to Tetramorium cognatum species complex workers

Distribution
Broadly distributed in Madagascar. The southernmost locality is Andohahela in the southeast; from there the species ranges with few interruptions up to Montagne d’Ambre at the northern tip of Madagascar. In addition to the eastern and northern forest belt, T. proximum is also found in the few isolated humid forests located further west, such as Analavelona, Isalo, and Ambohijanahary. (Hita Garcia and Fisher 2014)

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar.

Habitat
Tetramorium proximum is found in rainforests or montane rainforests at elevations from 25 to 1680 m.

Nomenclature

 *  proximum. Tetramorium proximum Bolton, 1979: 137, figs. 5, 6 (w.q.) MADAGASCAR.

Worker
Hita Garcia and Fisher (2014) - (N=12). HL 0.72–0.88 (0.78); HW 0.65–0.81 (0.72); SL 0.49–0.60 (0.54); EL 0.18–0.20 (0.19); PH 0.34–0.40 (0.37); PW 0.49–0.60 (0.54); WL 0.92–1.07 (0.98); PSL 0.12–0.18 (0.15); PTL 0.15–0.19 (0.18); PTH 0.29–0.35 (0.32); PTW 0.18–0.23 (0.21); PPL 0.19–0.23 (0.22); PPH 0.29–0.35 (0.31); PPW 0.28–0.34 (0.31); CI 89–94 (92); SI 74–76 (75); OI 24–28 (26); DMI 53–58 (55); LMI 37–40 (38); PSLI 17–21 (19); PeNI 37–42 (39); LPeI 52–60 (56); DPeI 111–130 (120); PpNI 52–61 (57); LPpI 65–74 (69); DPpI 135–153 (145); PPI 135–160 (148).

Head much longer than wide (CI 89–94); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae strongly developed, noticeably raised, diverging posteriorly, and either reaching or ending shortly before posterior head margin. Antennal scrobes present and distinct but weak, shallow and without clear and distinct posterior and ventral margins. Antennal scapes short, not reaching posterior head margin (SI 74–76). Eyes relatively large (24–28). Mesosomal outline in profile flat to weakly convex, relatively low and long (LMI 37–40), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove weakly to moderately developed. Propodeal spines short to medium-sized, elongate-triangular, and usually acute (PSLI 17–21), propodeal lobes short, triangular, and blunt or acute, always much shorter than propodeal spines. Petiolar node in profile high nodiform with well-rounded antero- and posterodorsal margins and strongly convex dorsum, around 1.7 to 1.9 times higher than long (LPeI 52–60), anterior and posterior faces approximately parallel, antero- and posterodorsal margins situated at about same height; petiolar node in dorsal view around 1.1 to 1.3 times wider than long (DPeI 111–130), in dorsal view pronotum around 2.4 to 2.7 times wider than petiolar node (PeNI 37–42). Postpetiole in profile subglobular and weakly anteroposteriorly compressed, around 1.4 to 1.5 times higher than long (LPpI 65–74); in dorsal view around 1.3 to 1.5 times wider than long (DPpI 135–153), pronotum around 1.7 to 1.9 times wider than postpetiole (PpNI 52–61). Postpetiole in profile appearing approximately of same volume as petiolar node, and both nodes of approximately similar height; postpetiole in dorsal view between 1.3 to 1.6 times wider than petiolar node (PPI 135–160). Mandibles completely unsculptured, smooth, and shiny; clypeus longitudinally rugose with usually three to five rugae, median ruga usually distinct and fully developed, sometimes partly reduced or broken, one or two weaker rugae present on each side; cephalic dorsum between frontal carinae longitudinally rugose with six to nine rugae, rugae running from posterior clypeal margin to posterior head margin, but often interrupted, splitting up or with cross-meshes; scrobal area mostly unsculptured; lateral head reticulate-rugose to longitudinally rugose. Ground sculpture on head weakly to moderately punctate. Dorsum of mesosoma mostly reticulate-rugose with smaller proportions of irregularly longitudinally rugose sculpture medially; lateral mesosoma mostly irregularly longitudinally rugose. Forecoxae mostly unsculptured, smooth, and shining, sometimes with traces of ground sculpture. Ground sculpture on mesosoma usually weak to absent. Both waist segments and gaster fully unsculptured, smooth, and shining. Dorsum of head with several pairs of long, fine, standing hairs; mesosoma with four to nine pairs of long, fine, standing hairs, usually with five or six ranging from anterior pronotum to metanotal groove, rarely propodeum with one pair anteriorly; waist segments and first gastral tergite without any standing hairs; appressed pubescence on first gastral tergite highly variable: ranging from short to very short and relatively scarce to relatively long and dense. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae usually with appressed, rarely decumbent, hairs. Head, mesosoma, waist segments, and gaster light brown to reddish brown, rarely of darker brown; mandibles, antennae, and legs lighter, usually light yellowish brown.

Type Material
Hita Garcia and Fisher (2014) - Holotype, pinned worker, MADAGASCAR, Toamasina, Périnet & vicinity, 18.82667°S, 48.44778°E, rainforest, rotten wood, 18.III.1969 (W. L. Brown) (: MCZ_Holotype_32264) [examined]. Paratypes, ten pinned workers and one pinned queen with same data as holotype (: CASENT0102341; CASENT0102342; CASENT0235211; MCZ: MCZ_Paratype_32264). [Note: the GPS data of the type locality was not provided either by the locality label or the original description. The data presented above is based on our own georeferencing of the Périnet=Andasibe area and should be considered an approximation and not the exact position of the type locality.]