Tetramorium dysalum Bolton, 1979

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 : 63-65

Tetramorium dysalum Bolton, 1979

(figs 79, 80, 95, 96, 97, 98, 99, 100)

Tetramorium dysalum Bolton, 1979:141 . Holotype worker, MADAGASCAR, Perinet and vicinity , rainforest , 17.III.1969 (W.L. Brown) ( MCZ) [examined]. Paratypes, 39 workers and one dealate queen with same data as holotype ( MCZ; BMNH) [examined] .

Diagnosis

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.

Description

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.

Notes

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

This species displays a remarkable size variation, as can be seen in the measurements given above. 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. In Anjanaharibe, Manongarivo, and Amparihibe both forms can be found together, and this interesting division into two size classes led us to consider splitting these forms into two distinct species. However, after examining all available specimens, we found several intermediates (HW 0.74–0.77; PSLI 36–39) that connect both morphometric ranges, although we must admit that the number of intermediates is very small, and are mainly found in Ambanizana, Manongarivo, and Binara. We currently consider all the material treated here as T. dysalum as a single but very size-variable species, yet cannot rule out the possibility that both forms represent distinct but comparatively cryptic species. The intermediates could be tentative hybrids between the small and the large forms. However, this explanation seems unlikely as the intermediates are only rarely found in combination with both size classes. Instead, the smaller form is often the only one encountered, sometimes together with the larger form or with a few intermediates. It is also probable that the material treated as T. dysalum includes several currently unrecognised species, but the diagnostic characters distinguishing them have not yet been identified. The use of molecular techniques and additional material might improve this situation.

Another possibility could be the presence of 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.

Apart from the variation described above, most other morphological and morphometric characters are very stable throughout the whole distribution range, and T. dysalum is generally easily recognisable within its species group due to its combination of very short antennal scapes (SI 64–69), long to very long propodeal spines (PSLI 30–43), and a mesosomal dorsum with distinct and well-developed longitudinal rugae. The sharply defined anterodorsal margin of the petiolar node with the petiolar dorsum tapering backwards posteriorly is unique in the group, since the anterodorsal margin is usually less sharply developed in the other species. However, as already mentioned in the notes on the T. dysalum group, larger specimens of T. dysalum could be confused with some species of the T. tortuosum group. Tetramorium pleganon and few undescribed species possess a petiolar node shape which is close to the larger T. dysalum specimens, but the two can be easily separated in other ways. In T. pleganon and allies the petiolar node and usually the first gastral tergite are strongly sculptured, whereas the larger specimens of T. dysalum have a weakly sculptured petiolar node and a completely unsculptured first gastral tergite.

Material examined

MADAGASCAR: Amparihibe, II.–III.2003 (K.A. Jackson & D. Carpenter); Antananarivo, Forêt de galerie, Andranorovitra, 24.0 km NNE Ankazobe, 18.11243 S, 47.19757 E, 1491 m, disturbed gallery montane forest, 2.– 3.VI.2008 (B.L. Fisher et al.); Antananarivo, Réserve Spéciale d'Ambohitantely, Forêt d Ambohitantely, 20.9 km 72° NE d Ankazobe, 18.22528 S, 47.28683 E, 1410 m, montane rainforest, 17.–22.IV.2001 (B.L. Fisher, C. Griswold et al.); Antsiranana, Forêt de Binara, 9.4km 235° SW Daraina, 13.26333 S, 49.6 E, 1100 m, 5.XII.2003 (B.L. Fisher); Antsiranana, 7 km N Joffreville [camp 2 of Fisher], 12.33333 S, 49.25 E, 360 m, in dry forest, 27.IV.–13.V.2001 (R. Harin'Hala); Antsiranana, Parc National de Marojejy, Manantenina River, 28.0 km 38° NE Andapa, 8.2 km 333° NNW Manantenina, 14.43667 S, 49.775 E, 450 m, rainforest, 12.–25.XI.2003 (B.L. Fisher et al.); Antsiranana, Parc National de Marojejy, Manantenina River, 27.6 km 35° NE Andapa, 9.6 km 327° NNW Manantenina, 14.435 S, 49.76 E, 775 m, rainforest, 15.–18.XI.2003 (B.L. Fisher et al.); Antsiranana, Parc National de Marojejy, Antranohofa, 26.6 km 31° NNE Andapa, 10.7 km 318° NW Manantenina, 14.44333 S, 49.74333 E, 1325 m, montane rainforest, 18.–20.XI.2003 (B.L. Fisher); Antsiranana, Parc National Montagne d'Ambre, 12° 31' S, 49° 11' E, 1000 m, rainforest, 12.VIII.1992 (G.D. Alpert); Antsiranana, Parc National Montagne d'Ambre, Petit Lac, 12° 31' S, 49° 10' E, 1000 m, montane rainforest, 19.VIII.1992 (G.D. Alpert); Antsiranana, Parc National Montagne d'Ambre, 12.53333 S, 49.16667 E, 1100 m, montane rainforest, 23.–28.XI.1993 (C. Griswold et al.); Antsiranana, Parc National Montagne d'Ambre, 3.6 km 235° SW Joffreville, 12.53444 S, 49.1795 E, 925 m, 20.– 26.I.2001 (B.L. Fisher, C. Griswold et al.); Antsiranana, Parc National Montagne d'Ambre, Antomboka, 12.50035 S, 49.175 E, 885 m, montane rainforest, 16.XI.2007 (B.L. Fisher et al.); Antsiranana, Rés. Anjanaharibe-Sud, 6.5 km SSW Befingotra, 14.75 S, 49.5 E, 875 m, rainforest, 19.X.1994 (B.L. Fisher); Antsiranana, Rés. AnjanaharibeSud, 9.2 km WSW Befingotra, 14.75 S, 49.46667 E, 1200 m, montane rainforest, 9.XI.1994 (B.L. Fisher); Antsiranana, Rés. Anjanaharibe-Sud, 11.0 km WSW Befingotra, 14.75 S, 49.45 E, 1565 m, montane rainforest, 16.XI.1994 (B.L. Fisher); Antsiranana, R.S. Manongarivo, 14.5 km 220° SW Antanambao, 13.99833 S, 48.42833 E, 1175 m, montane rainforest, 20.X.1998 (B.L. Fisher); Fianarantsoa, 45km S. Ambalavao, rainforest, 22.21667 S, 47.01667 E, 785 m, 25.IX.–1.X.1993 (B.L. Fisher); Fianarantsoa, Parc National d'Isalo, 9.1 km 354° N Ranohira, 22.48167 S, 45.46167 E, 725 m, gallery forest, 27.–31.I.2003 (B.L. Fisher, C. Griswold et al.); Fianarantsoa, Parc Nationale Ranomafana, Talatakely, 21.24833 S, 47.42667 E, in guava forest, 9.–26.IV.1998 (C. Griswold, D. Kavanaugh, et al.); Fianarantsoa, Parc Nationale Ranomafana, Belle Vue trail, 21.2665 S, 47.42017 E, 1020 m, mixed tropical forest, 15.–22.XI.2001 (R. Harin'Hala); Fianarantsoa, Parc National de Ranomafana, Vatoharanana River, 4.1 km 231° SW Ranomafana, 21.29 S, 47.43333 E, 1100 m, montane rainforest, 27.– 31.III.2003 (B.L. Fisher, C. Griswold et al.); Fianarantsoa, Rés. Andringitra, 43 km S Ambalavao , 22.23333 S, 47 E, 825 m, rainforest, 4.–5.X.1993 (B.L. Fisher); Fianarantsoa, R.S. Ivohibe, 7.5 km ENE Ivohibe, 22.47 E, 46.96 E, 900 m, rainforest, 7.–12.VII.1997 (B.L. Fisher); Fianarantsoa, R.S. Ivohibe 8.0 km E Ivohibe, 22.48333 S, 46.96833 E, 1200 m, montane rainforest, 15.–21.X.1997 (B.L. Fisher); Fianarantsoa, 9.0 km NE Ivohibe, 22.42667 S, 46.93833 E, 900 m, rainforest, 12.–17.XI.1997 (B.L. Fisher); Fianarantsoa, 3 km W Ranomafana, nr. Ifanadiana, 21° 15' S, 47° 25' E, 950 m, rainforest, 27.IV.1989 (P.S. Ward); Toamasina, Ambanizana, Parc National Masoala, 15.57167 S, 50.00611 E, 900–950 m, 26.II.–6.III.2003 (D. Andriamalala, D. Silva, et al.); Toamasina, Ambanizana, Parc National Masoala, 15.57222 S, 50.00694 E, 930–1110 m, 2.–6.III.2003 (D. Andriamalala, D. Silva, et al.); Toamasina, Ambohitsitondroina, 6.9 km NE Ambanizana, 15.56667 S, 50 E, 825 m, rainforest, 2.XII.1993 (B.L. Fisher); Toamasina, Andranobe, 5.3 km SSE Ambanizana, 15.66667 S, 49.96667 E, 425 m, 19.– 21.XI.1993 (B.L. Fisher); Toamasina, Andranobe, 6.3 km S Ambanizana, 15.68131 S, 49.958 E, 25 m, 15.68131 S, 49.958 E, 25 m, 13.–15.XI.1993 (B.L. Fisher); Toamasina, vic. Andasibe (=Perinet), 950–980 m, 2.–6.II.1976 (W.L. & D.E. Brown); Toamasina, 6 km ESE Andasibe (=Perinet), 18° 57' S, 48° 28' E, 900 m, rainforest, 17.XI.1990 (P.S. Ward); Toamasina, F.C. Didy, 18.19833 S, 48.57833 E, 960 m, rainforest, 16.–23.XII.1998 (H.J. Ratsirarson); Toamasina, Mangabe island, Antongil, rainforest, 19.II.1977 (W.L. & D.E. Brown); Toamasina, Montagne d'Anjanaharibe, 18.0 km 21° NNE Ambinanitelo, 15.18833 S, 49.615 E, 470 m, rainforest, 8.– 12.III.2003 (B.L. Fisher, C. Griswold et al.); Toamasina, Montagne d'Anjanaharibe, 19.5 km 27° NNE Ambinanitelo, 15.17833 S, 49.635 E, 1100 m, montane rainforest, 12.–16.III.2003 (B.L. Fisher, C. Griswold et al.); Toamasina, Montagne d'Akirindro 7.6 km 341° NNW Ambinanitelo, 15.28833 S, 49.54833 E, 600 m, rainforest, 17.–21.III.2003 (B.L. Fisher, C. Griswold et al.); Toamasina, P.N. Mantadia, 18.79167 S, 48.42667 E, 895 m, 28.XI.–1.XII.1998 (H.J. Ratsirarson); Toamasina, Périnet & vic., rainforest, 17.III.1969 (W.L. Brown); Toamasina, Réserve Spéciale Ambatovaky, Sandrangato river, 16.80561 S, 49.29507 E, 480 m, rainforest, 27.X.2010 (B.L. Fisher et al.); Toliara, Parc National d'Andohahela, Col du Sedro, 3.8 km 113° ESE Mahamavo, 37.6 km 341° NNW Tolagnaro, 24.76389 S, 46.75167 E, 900 m, montane rainforest, 21.–25.I.2002 (B.L. Fisher, C. Griswold et al.); Toliara, Rés. Andohahela, 11 km NW Enakara, 24.56667 S, 46.83333 E, 800 m, 17.XI.1992 (B.L. Fisher); Toliara, Réserve Spéciale d'Ambohijanahary, Forêt d'Ankazotsihitafototra, 35.2 km 312° NW Ambaravaranala, 18.26667 S, 45.40667 E, 1050 m, montane rainforest, 13.–17.I.2003 (B.L. Fisher, C. Griswold et al.).