Tetramorium cavernicola Hita Garcia & Fisher

Hita Garcia, Francisco & Fisher, Brian L., 2015, Taxonomy of the hyper-diverse ant genus Tetramorium Mayr in the Malagasy region (Hymenoptera, Formicidae, Myrmicinae) - first record of the T. setigerum species group and additions to the Malagasy species groups with an updated illustrated identification key, ZooKeys 512, pp. 121-153 : 144-146

Taxon classification Animalia Hymenoptera Formicidae

Tetramorium cavernicola Hita Garcia & Fisher sp. n. Figs 6A, E, 29B, 30

Type material.

Holotype, pinned worker, MADAGASCAR, Antsiranana, Réserve Spéciale d’Ankarana, Andrafiabe, 12.92968 S, 49.05983 E, 59 m, in cave, ground nest, collection code BLF32473, 26.XI.2013 (B. Fisher et al.) (CASC: CASENT0247028). Paratypes, 15 pinned workers with same data as holotype (CASC: CASENT0247022; CASENT0247023; CASENT0247024; CASENT0247025; CASENT0247026; CASENT0247027; CASENT0247028; CASENT0247357; CASENT0247358; CASENT0248742; CASENT0248745; CASENT0248746; CASENT0373132; HLMD: CASENT0247029; MHNG: CASENT0248743; NHMB: CASENT0248744); and three pinned workers with same data as holotype except collection code BLF32472 and collected as ground foragers (BMNH: CASENT0247021; CASC: CASENT0247020; MCZ: CASENT0373133).

Non-type material.

MADAGASCAR: Antsiranana, Réserve Spéciale d’Ankarana, Andrafiabe, 12.92968 S, 49.05983 E, 59 m, 26.XI.2013 (B. Fisher et al.).

Diagnosis.

Tetramorium cavernicola differs from all other Malagasy congeners by the following combination of characters: 12-segmented antennae; anterior clypeal margin entire and convex; lateral clypeus not modified into tooth or denticle; antennal scape very long (SI 120-123); mesosoma in profile relatively low and slender (LMI 35-36); and propodeum armed with very short teeth/spines (PSLI 7-11).

Worker measurements

(N=15). HL 0.74-0.78 (0.76); HW 0.58-0.61 (0.60); SL 0.71-0.75 (0.72); EL 0.14-0.15 (0.14); PH 0.32 –– 0.35 (0.33); PW 0.45-0.48 (0.46); WL 0.92-0.99 (0.95); PSL 0.06-0.08 (0.07); PTL 0.17-0.19 (0.18); PTH 0.22-0.24 (0.23); PTW 0.21-0.23 (0.22); PPL 0.22-0.24 (0.23); PPH 0.24-0.25 (0.25); PPW 0.26-0.28 (0.27); CI 77-79 (78); SI 120-123 (122); OI 23-26; DMI 47-50 (49); LMI 35-36 (35); PSLI 7-11 (9); PeNI 47-49 (47); LPeI 73-79 (77); DPeI 121-127 (123); PpNI 56-60 (58); LPpI 90-98 (94); DPpI 113-123 (117); PPI 120-127 (124).

Worker description.

Head much longer than wide (CI 77-79); posterior head margin weakly to moderately concave. Anterior clypeal margin entire and convex. Frontal carinae strongly developed, moderately raised, usually becoming weaker after posterior eye level, approaching or ending at posterior head margin; antennal scrobes very weak to absent. Antennal scapes very long, weakly surpassing posterior head margin (SI 120-123). Eyes moderately large (OI 23-26). Mesosomal outline in profile relatively flat, elongate and low (LMI 35-36), weakly marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent. Propodeum armed with short, triangular teeth (PSLI 7-11), propodeal lobes moderately developed, triangular to elongate-triangular, slightly longer and broader than propodeal teeth. Petiolar node nodiform with moderately rounded antero- and posterodorsal margins, in profile between 1.2 and 1.4 times higher than long (LPeI 73-79), anterior and posterior faces not parallel, node weakly narrowing towards dorsum, anterodorsal and posterodorsal margins situated at about same height and both weakly to moderately angled, petiolar dorsum flat to very weakly convex; node in dorsal view around 1.2 to 1.3 times wider than long (DPeI 121-127), in dorsal view pronotum around 2.0 to 2.1 times wider than petiolar node (PeNI 47-49). Postpetiole in profile approximately globular, around 1.0 to 1.1 times higher than long (LPpI 90-98); in dorsal view around 1.1 and 1.2 times wider than long (DPpI 113-123), pronotum around 1.7 to 1.8 times wider than postpetiole (PpNI 56-60). Postpetiole in profile appearing distinctly more voluminous than petiolar node, postpetiole in dorsal view around 1.2 to 1.3 times wider than petiolar node (PPI 120-127). Mandibles striate; clypeus longitudinally rugose/rugulose with well-developed median ruga and usually one or two weaker, sometimes irregular, lateral rugae/rugulae on each side; cephalic dorsum between frontal carinae anteriorly towards posterior clypeal margin with three or four distinct but irregularly shaped longitudinal rugae with numerous cross-meshes, halfway between eye level and posterior head margin fluent transition to well-developed rugoreticulum ranging to posterior head margin; scrobal area only weakly sculptured, remainder of lateral head clearly reticulate-rugose. Mesosoma laterally and dorsally conspicuously reticulate-ru gose; forecoxae unsculptured, smooth, and shining. Petiole and postpetiole irregularly rugulose, better developed on dorsum than sides. First gastral tergite unsculptured, smooth, and shiny. Ground sculpture on cephalic dorsum between frontal carinae weak, distinctly reticulate-punctate on lateral head, mesosoma, and waist segments, absent from gaster. All dorsal surfaces of body with short to moderately long, thick, and apically blunt pilosity; appressed pubescence on first gastral tergite strongly reduced to absent. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with decumbent to suberect hairs. Head and mesosoma reddish brown; waist segments lighter in colour, usually orange brown; mandibles, antennae, and legs yellowish brown.

Etymology.

The name of the new species is a Latin noun and means "cave dweller" or "cave inhabitant". It refers to the microhabitat where the type series was collected. The species epithet is a nominative noun in apposition.

Distribution and biology.

Currently, Tetramorium cavernicola is only known from Ankarana (Fig. 30D), where it was collected from a cave. The collection locality and the fact that the species is not known from outside the cave imply that Tetramorium cavernicola might be a specialised, cave-adapted ant. The generally very slender body and very long antennae and legs also support cave specialisation. Nevertheless, we do not consider the new species an obligate cave inhabitant. Arthropods that have evolved a cave-obligate lifestyle usually have a distinct set of morphological adaptations: reduction or loss of eyes, pigments, and wings; thinning of the cuticle; elongate antennae and legs; and slender body ( Christiansen 1962; Culver 1982; Barr 1985). Yet the eyes, pigment, and wings in Tetramorium cavernicola are clearly not reduced since its eyes are always well developed, as are the wings in the queen and male castes, and the body colouration is brownish. In addition, we cannot detect any thinning of the cuticle. The slender gestalt and long antennae and legs could argue for cave adaptation, but are actually very typical of most species in the Tetramorium setigerum group. The antennae and legs of Tetramorium dolichosum Bolton and Tetramorium perlongum Santschi (Fig. 29E, F) are much longer than in Tetramorium cavernicola , even though these species do not live in caves. Tetramorium cavernicola appears to nest in the ground since most of the type series was collected from a ground nest, but no additional natural history data exists for this species.

Discussion.

Tetramorium cavernicola is a very distinctive element of the Malagasy Tetramorium fauna and cannot be mistaken for any other congener based on the diagnosis provided above. There are some morphological similarities to the two species of the Tetramorium tosii group, as outlined earlier, but the distinction between these is easily found by comparing the shape of the head, the length of the antennal scapes, and the propodeal spines. In Tetramorium cavernicola the head is noticeably thinner (CI 77-79) and the antennal scapes are much longer (SI 120-123) while the propodeal spines are reduced to short teeth (PSLI 7-11). By contrast, the species in the Tetramorium tosii group have a thicker head (CI 85-91), much shorter scapes (SI 79-104), and much longer propodeal spines (PSLI 30-49).

Variation.

Since Tetramorium cavernicola is only known from the type locality, there is no observable intraspecific variation.