Tetramorium dysalum

It can be encountered in most rainforests and montane rainforests of eastern and northern Madagascar, and it occurs at altitudes of 25 to 1565 m.

Identification
A member of the Tetramorium dysalum-species group

Hita Garcia and Fisher (2012) - Tetramorium dysalum can be well recognised within the species group due to its unique character combination of: very short antennal scapes (SI 64 - 69); propodeal spines stout, long and often curved backwards (PSLI 30 - 43); unsculptured mandibles; mesosomal dorsum with longitudinally rugose sculpture.

This species displays a remarkable size variation. Generally, there seem to be two size classes within this species that differ in several aspects. Smaller specimens (HW 0.53 - 0.69) are found throughout the whole range, and tend to have shorter propodeal spines (PSLI 30 - 34), and a stronger anteroposteriorly compressed and sculptured petiolar node. The larger specimens (HW 0.80 - 0.90), which are much rarer and only found in few localities (Marojejy, Anjanaharibe, Manongarivo, and Amparihibe), have larger spines (PSLI 40 - 43) and a less anteroposteriorly compressed and sculptured petiolar node.

Distribution
Tetramorium dysalum has a very wide distribution range in Madagascar, and can also be found on Nosy Be.

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar.

Castes
Hita Garcia and Fisher (2012) - This species displays a remarkable size variation. It is possible there are morphologically distinct subcastes in this species. Within the genus Tetramorium it is common to find remarkable intraspecific size variation without the development of distinct subcastes (Bolton, 1980; Hita Garcia et al., 2010; Hita Garcia & Fisher, 2011). Very common and widely distributed species are the most likely to display large size variations. Yamane and Jaitrong (2011) recently described a new species from Laos which appears to possess a morphologically distinct major worker subcaste. The apparent division into minor and major subcastes is based on differences in pilosity, head shape, and sculpture. This variation is comparatively common in several Afrotropical and Malagasy Tetramorium, and is usually considered a regular intraspecific size variation that includes minor differences in pilosity, head shape, and sculpture. Nevertheless, both subcastes described by Yamane and Jaitrong (2011) were collected from a single nest, which provides good evidence for this polymorphism. In the case of T. dysalum, it would be more difficult to recognise the two observed size classes as polymorphic subcastes, and we are very reluctant to do so. Despite examining a large number of specimens, more material, especially from nest collections, is necessary before drawing such a conclusion.

Nomenclature

 *  dysalum. Tetramorium dysalum Bolton, 1979: 141, fig. 24 (w.q.) MADAGASCAR. See also: Hita Garcia & Fisher, 2012: 63.

Worker
Hita Garcia and Fisher (2012) - HL 0.54 - 0.91 (0.70); HW 0.53 - 0.90 (0.70); SL 0.35 - 0.60 (0.47); EL 0.11 - 0.20 (0.14); PH 0.27 - 0.45 (0.35); PW 0.38 - 0.67 (0.51); WL 0.64 - 1.15 (0.87); PSL 0.16 - 0.38 (0.24); PTL 0.10 - 0.19 (0.15); PTH 0.21 - 0.36 (0.29); PTW 0.15 - 0.28 (0.21); PPL 0.16 - 0.28 (0.21); PPH 0.18 - 0.33 (0.26); PPW 0.21 - 0.35 (0.27); CI 98 - 103 (100); SI 64 - 69 (67); OI 18 - 23 (21); DMI 55 - 62 (59); LMI 39 - 42 (40); PSLI 30 - 43 (34); PeNI 38 - 44 (41); LPeI 45 - 58 (52); DPeI 128 - 155 (142); PpNI 51 - 57 (54); LPpI 74 - 88 (80); DPpI 125 - 147 (131); PPI 121 - 140 (131) (25 measured).

Head generally as long as wide (CI 98 - 103). Anterior clypeal margin with distinct median impression. Frontal carinae well-developed, after posterior eye margin distinctly weaker, ending between posterior eye margin and posterior head margin. Antennal scrobes faint, narrow. Antennal scapes short, not reaching posterior head margin (SI 64 - 69). Eyes comparatively small to moderate (OI 18 - 23). Mesosomal outline in profile weakly convex, distinctly marginate from lateral to dorsal mesosoma, promesonotal suture absent, metanotal groove usually absent, rarely weakly present; mesosoma comparatively stout and compact (LMI 39 - 42). Propodeal spines stout, long to very long, and often curved backwards (PSLI 30 - 43). Propodeal lobes short and broadly triangular. Petiolar node in profile weakly cuneiform to moderately nodiform, approximately 1.7 to 2.2 times higher than long (LPeI 45 - 58), anterodorsal margin sharply developed and situated higher than posterodorsal, dorsum strongly tapering backwards posteriorly; node in dorsal view between 1.1 to 1.4 times longer than wide (DPeI 128 - 155). Postpetiole in profile rounded, approximately 1.7 to 2.2 times higher than long (LPpI 74 - 88), in dorsal view between 1.2 to 1.5 times wider than long (DPpI 125 - 147). Postpetiole in profile appearing a bit less voluminous than petiolar node, in dorsal view approximately 1.2 to 1.4 times wider than petiolar node (PPI 121 - 140). Mandibles always unsculptured, smooth and shiny; clypeus with variable sculpture, generally with few irregular, longitudinal rugae and medially relatively unsculptured, sometimes with more regularly arranged longitudinal rugae; cephalic dorsum between frontal carinae with eight to 13 longitudinal, mostly unbroken rugae, most rugae running from anterior clypeal margin to posterior head margin; scrobal area mostly unsculptured, smooth and shining, remainder of lateral and ventral head with longitudinal rugae. Ground sculpture generally faint, sometimes moderately developed. Mesosoma laterally generally with irregular longitudinal rugae, sometimes lateral pronotum almost unsculptured; mesosomal dorsum packed with comparatively regular longitudinal rugae. Petiolar node laterally and posteriorly usually with weak, irregular rugulae and often with weak reticulate-punctate ground sculpture, petiolar dorsum almost always unsculptured, smooth, and shiny. Postpetiole generally with irregular longitudinal rugulae and often with reticulate-punctate ground sculpture. Gaster always unsculptured, smooth and shining. All dorsal surfaces of body with long, erect or suberect pilosity. Head, mesosoma, waist segments, and gaster uniformly brown to dark brown, often mandibles, antennae, and legs of lighter brown.

Type Material
Hita Garcia and Fisher (2012) - Tetramorium dysalum Bolton, 1979:141. Holotype worker, MADAGASCAR, Perinet and vicinity, rainforest, 17.III.1969 (W.L. Brown) [examined]. Paratypes, 39 workers and one dealate queen with same data as holotype [examined].