Tetramorium venator Hita Garcia

Hita Garcia, Francisco & Fisher, Brian L., 2014, The ant genus Tetramorium Mayr in the Afrotropical region (Hymenoptera, Formicidae, Myrmicinae): synonymisation of Decamorium Forel under Tetramorium, and taxonomic revision of the T. decem species group, ZooKeys 411, pp. 67-103 : 89-93

Tetramorium venator Hita Garcia sp. n. Figs 3, 4D, 6B, 7C, 7D, 12

Type material.

Holotype, pinned worker, KENYA, Western Kenya, Kakamega Forest, Bunyala Forest Fragment, 0.37889N, 34.69917E, 1448 m, disturbed primary forest, Kakamega 2008 survey, leaf litter, pitfall trap, Transect 35, position 10 m, 1.VIII.2008 (G. Fischer) (CASC: CASENT0195574). Paratypes, six pinned workers with same data as holotype (BMNH: CASENT0195625; CASC: CASENT0217165; BMNH: CASENT0195625; LACM: CASENT0195627; MCZ: CASENT0195624; NMK: CASENT0195626; ZFMK: CASENT0195623).

Non-type material.

CAMEROON: Centre, Mbalmayo, 1.XI.1993 (N. Stork); Centre, Ottotomo, 24.IV.1986 (A. Dejean); Est, Abong Mbang, 28.VI.1988 (A. Dejean); Sud, Bondé Forest, N’kolo village, 27.5 km 155°SSE Elogbatindi, 3.22167N, 10.24667E, 40 m, rainforest, 12.IV.2000 (B.L. Fisher); Sud, Res. de Faune de Campo, Massif des Mamelles, 15.1 km 84°E Ébodjé, 2.59417N, 9.9595E, 180 m, rainforest, 4.IV.2000 (B.L. Fisher); Sud, Res. de Faune de Campo, 2.16 km 106°ESE Ébodjé, 2.56783N, 9.84433E, 10 m, littoral rainforest, 9.IV.2000 (B.L. Fisher); Sud, P. N. Campo, 43.3 km 108°ESE Campo, 2.2825N, 10.20617E, 290 m, rainforest, 7.IV.2000 (B.L. Fisher); Sud-Ouest, Bimbia Forest, 7.4 km 119°ESE Limbe, 3.98183N, 9.2625E, 40 m, 14.IV.2000 (B.L. Fisher); Sud-Ouest, Korup N. P., 6.9 km 317°NW Mundemba, 5.016N, 8.864E, 110 m, rainforest, 19.IV.2000 (B.L. Fisher); CENTRAL AFRICAN REPUBLIC: Prefecture Sangha-Mbaéré, Parc National Dzanga-Ndoki, Mabéa Bai, 21.4 km 53°NE Bayanga, 3.03333N, 16.41E, 510 m, rainforest, 1.-7.V.2001 (B.L. Fisher); DEMOCRATIC REPUBLIC OF CONGO: Epulu, 750 m, 1.38333N, 28.58333E, rainforest, 1.XI.1995 (S.D. Torti); Kikwit, Kinzambi, 27.III.1984 (A. Dejean); 44 miles E. of Kileba, 1110 m, 16.I.1958 (E.S. Ross & R.E. Leech); GABON: La Makandé Forêt des Abeilles, 1.I.-1.II.1999 (S. Lewis); Ogooué-Ivindo, Makokou, C.N.R.S., 10.VII.1974 (W. Gotwald); Ogooue-Maritime, Réserve des Monts Doudou; 24.3km 307°NW Doussala, 2.2225S, 10.40583E, 370 m, coastal lowland rainforest, 5.-12.III.2000 (S. van Noort); Ogooue-Maritime, Aire d’Exploit. Rationnelle de Faune des Monts Doudou, 24.3 km 307°NW Doussala, 2.22639S, 10.40972E, 375 m, rainforest, 6.III.2000 (B.L. Fisher); Ogooue-Maritime, Reserve de la Moukalaba-Dougoua, 12.2 km 305°NW Doussala, 2.28333S, 10.49717E, 110 m, coastal lowland rainforest, sited within forest, 24.II.-3.III.2000 (S. van Noort); Ogooue-Maritime, Reserve de Faune de la Moukalaba-Dougoua, 10.8 km 214°SW Doussala, 2.42267S, 10.54533E, 110 m, rainforest, 29.II.2000 (B.L. Fisher); Ogooue-Maritime, Reserve de Faune de la Moukalaba-Dougoua, 12.2 km 305°NW Doussala, 2.31667N, 10.53333E, 110 m, rainforest, 1.III.2000 (B.L. Fisher); Woleu-Ntem, 31.3 km 108°ESE Minvoul, 2.08N, 12.40667E, 600 m, rainforest, 7.-15.II.1998 (B.L. Fisher); GHANA: Akwapim, Tafo, 19.I.1970 (B. Bolton); Ashanti, Poano, cocoa, 9.IX.1992 (R. Belshaw); Atewa Forest Reserve, near Kibi, primary forest, 24.III.1992 (R. Belshaw); Eastern, Kade, 1.I.1992 (R. Belshaw); Enchi, 17.V.1969 (D. Leston); Esunkawkaw Forest Reserve, primary forest, 27.X.1992 (R. Belshaw); Nkawanda near Nkawkaw, secondary forest, 12.XII.1991 (R. Belshaw); Portrase, 1.III.1992 (R. Belshaw); KENYA: Western Kenya, Kakamega Forest, Bunyala Forest Fragment, 0.37889N, 34.69917E, 1448 m, disturbed primary forest, 1.VIII.2008 (G. Fischer); LIBERIA: Monrovia, 5.VII.1957 (E.S. Ross & R.E. Leech); TANZANIA: Kigoma Region, Gombe Stream National Park, 4.7S, 29.616667E, 915-1012 m, 29.XII.2009-12.I.2010 (R. O’Malley); UGANDA: Semuliki NP, 00.83556, 30.15542 ± 200 m, 676 m, rainforest, 30.-31.VII.2012 (B.L. Fisher et al.); Semuliki NP, 00.84483, 30.15052 ± 200 m, 680 m, rainforest, 2.VIII.2012 (B.L. Fisher et al.).

Diagnosis.

Tetramorium venator can be recognised by the following combination of characters: relatively smaller species (WL 0.87-0.98); very large eyes, largest in the group (OI 37-40); propodeum armed with very short, triangular, and moderately acute (PSLI 9-12); petiolar node in profile between 1.0 to 1.2 times higher than long (LPeI 90-100); dorsum of promesonotum unsculptured, smooth, and very shiny; head, mesosoma, waist segments, and gaster uniformly very dark brown to black, appendages of lighter brown.

Worker measurements

(N=25). HL 0.64-0.71 (0.67); HW 0.51-0.59 (0.54); SL 0.38-0.43 (0.40); EL 0.19-0.22 (0.21); PH 0.30-0.36 (0.32); PW 0.39-0.45 (0.41); WL 0.87-0.98 (0.92); PSL 0.06-0.09 (0.07); PTL 0.23-0.26 (0.25); PTH 0.25-0.29 (0.26); PTW 0.18-0.22 (0.20); PPL 0.21-0.25 (0.22); PPH 0.25-0.30 (0.26); PPW 0.25-0.30 (0.26); CI 79-83 (81); SI 70-75 (74); OI 37-40 (38); DMI 43-46 (44); LMI 33-37 (35); PSLI 9-12 (10); PeNI 45-51 (48); LPeI 90-100 (93); DPeI 76-85 (80); PpNI 63-67 (65); LPpI 80-86 (84); DPpI 115-124 (119); PPI 130-144 (135).

Worker description.

Head much longer than wide (CI 79-83); posterior head margin weakly concave. Anterior clypeal margin with distinct, but often shallow median impression. Frontal carinae strongly developed and noticeably raised forming dorsal margin of very well-developed antennal scrobes, curving down ventrally and anteriorly halfway between posterior eye margin and posterior head margin and forming posterior and ventral scrobe margins; antennal scrobes very well developed, deep and with clearly defined margins all around, median scrobal carina absent. Antennal scapes short, not reaching posterior head margin (SI 70-75). Eyes very large (37-40). Mesosomal outline in profile relatively flat, long and low (LMI 33-37), moderately marginate from lateral to dorsal mesosoma; promesonotal suture absent; metanotal groove present and distinct, but relatively shallow. Propodeum armed with very short, triangular, and moderately acute teeth (PSLI 9-12), propodeal lobes short, triangular to rounded, and usually blunt, in profile more or less of same length as propodeal teeth and appearing more voluminous than propodeal spines. Tibiae and femorae strongly swollen. Petiolar node nodiform with moderately rounded antero- and posterodorsal margins, in profile between 1.0 to 1.2 times higher than long (LPeI 90-100), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about same height and equally angled, petiolar dorsum usually conspicuously convex, sometimes only weakly so; node in dorsal view around 1.2 to 1.3 times longer than wide (DPeI 76-85), in dorsal view pronotum between 2.0 to 2.2 times wider than petiolar node (PeNI 45-51). Postpetiole in profile globular, approximately 1.2 times higher than long (LPpI 80-86); in dorsal view around 1.2 times wider than long (DPpI 115-124), pronotum approximately 1.5 to 1.6 times wider than postpetiole (PpNI 63-67). Postpetiole in profile appearing less voluminous than petiolar node, postpetiole in dorsal view between 1.3 to 1.5 times wider than petiolar node (PPI 130-144). Mandibles and clypeus usually fully unsculptured, smooth, and shining; cephalic dorsum between frontal carinae mostly unsculptured and shiny, median ruga present and distinct, cephalic dorsum also puncticulate to punctate across its length, close to posterior head margin especially pronounced; scrobal area unsculptured, smooth and very shiny; lateral head ventral of antennal scrobe mainly reticulate-rugose; ground sculpture on head usually weak to absent. Dorsum of mesosoma mostly unsculptured, smooth and shiny with scattered punctures, rarely with few traces of rugulae; lateral mesosoma mostly unsculptured and shiny, posteriorly irregularly rugose and conspicuously reticulate-punctate. Petiolar node and postpetiole only weakly sculptured, laterally usually superficially rugulose and punctate on lower half and more unsculptured on upper half, node dorsally mostly smooth; postpetiole mostly unsculptured, smooth and shiny with scattered punctures. First gastral tergite unsculptured, smooth, and shiny. Pilosity and pubescence greatly reduced: head with few pairs of moderately long, standing hairs, anterior pronotum with one long pair, waist segments sometimes with one long pair each, and sometimes first gastral tergite with one long pair; appressed pubescence present everywhere on body, but noticeable only on antennae, cephalic dorsum, legs, and first gastral tergite. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with appressed hairs. Head, mesosoma, waist segments, and gaster uniformly very dark brown to black, appendages of lighter brown.

Etymology.

The name of the new species is Latin and means “hunter” referring to the predatory lifestyle of Tetramorium venator . The species epithet is a nominative noun, and thus invariant.

Distribution and biology.

Tetramorium venator is the most widespread and abundant species of the group. It is found throughout much of the equatorial forest belt from Liberia in the west to Kenya in the east (Fig. 3). Even though there was no material from Benin, Togo, Nigeria, Equatorial Guinea or South Sudan available for this study, we expect that Tetramorium venator will be found in most or all of these countries. Based on the available data, this species lives in the leaf litter stratum of primary, secondary, or disturbed rainforests. Additionally, Tetramorium venator seems to be found at lower elevations in West and Central Africa, but also occurs at mid elevations further east in the eastern D.R. Congo, Tanzania, and Kenya, where it reaches its highest known elevation at the type locality at 1448 m. Based on unpublished stable isotope data from the type series, Tetramorium venator is a predatory species, and we assume that it feeds on termites. This is supported by some series from Cameroon that were collected while foraging in the nests of Cubitermes Wasmann.

Discussion.

Despite being common and collected fairly often prior to this study, most of the material of Tetramorium venator was identified and labelled as Tetramorium decem . Indeed, more than 90% of all the material listed as the latter species at the beginning of our revision turned out to be Tetramorium venator . Nevertheless, our revision shows that they are clearly not conspecific. Tetramorium venator is smaller in size (WL 0.87-0.98), has larger eyes (OI 37-40), shorter propodeal teeth (PSLI 9-12), a lower petiolar node (LPeI 90-100), and has a uniform body colouration. By contrast, Tetramorium decem is larger (WL 1.02-1.16), has smaller eyes (OI 32-34), longer propodeal spines (PSLI 17-19), a higher petiolar node (LPeI 77-82), and is distinctly bicoloured. Also, Tetramorium venator is a rainforest species while Tetramorium decem lives in savannah or woodland.

The abovementioned very large eyes of Tetramorium venator separate it also from Tetramorium ultor , which has smaller eyes (OI 33-36). In addition, Tetramorium ultor is also of a much lighter colour, usually light brown to chestnut brown, and prefers dry forest or woodland habitats. It should be noted, however, that Tetramorium ultor and Tetramorium venator are morphologically very close to each other and differ significantly only in eye size, colour and habitat preference. They could represent different ecotypes of the same species, one adapted to more shaded and humid forest versus one specialised to more arid savannah, woodland, and dry forest. Nevertheless, if this was true, then we would see some intermediate forms in transitional habitats, and there are none at present. As a matter of fact, Tetramorium venator is also found in secondary and disturbed rainforests. The type series was collected in a highly disturbed rainforest fragment in Kenya and the material from Gombe in Tanzania is from a rainforest-woodland mosaic. Both species are also separated by the Great Rift Valley, which separates different faunistic sub-regions of the Afrotropical region. We consider Tetramorium venator as a faunal element of the Guineo-Congolian forest zone, while we believe Tetramorium ultor is a species of the arid corridor running from East to Southern Africa. Based on the available material and African biogeography in general, we conclude that our two species hypothesis is more likely.

Furthermore, Tetramorium venator cannot be misidentified with either Tetramorium uelense or Tetramorium raptor since both possess strongly developed rugulose/rugose sculpture on the promesonotal dorsum that is absent in Tetramorium venator . At present, Tetramorium venator overlaps in its distribution with Tetramorium uelense and Tetramorium raptor in West and Central Africa. We think it might also overlap with Tetramorium decem and Tetramorium ultor in East Africa, even though it currently seems as if they are widely separated geographically. However, since the sampling is very patchy, especially in East Africa, much more Tetramorium decem and Tetramorium ultor material is likely to be collected with further inventories, and these two species will be found in close proximity to Tetramorium venator . Nevertheless, the latter species is restricted to more humid forest habitats, whereas Tetramorium decem and Tetramorium ultor clearly prefer more arid savannah, grassland, woodland and tropical dry forest.

Variation.

Intriguingly, even though Tetramorium venator is very broadly distributed in Equatorial Africa, there seems to be no significant intraspecific variation.