Tetramorium nama

Known and described from a collection of eight workers sampled from a single pitfall trap.

Identification
Hawkes 2020: Tetramorium nama is morphologically most similar to Tetramorium grandinode, with which it shares almost identical cephalic sculpture, but can be easily separated from this species by the following characters: in T. nama, the longitudinal costulae on the dorsum of the promesonotum run parallel and separate all the way to the anterior pronotal margin (Figure 2A), whereas in T. grandinode the costulae become strongly arcuate anteriorly, with lines from either side of the midline usually joining medially and forming a nested set of hyperbolic curves (Figure 2B); in T. nama, the petiole dorsum is much longer and has irregular concentric or whorled to irregularly transverse costulate sculpture (Figure 2A), while in T. grandinode the petiole node is very short and has strong transverse costulae on its dorsal surface (Figure 2B). The petiole node in T. nama is narrower (only slightly wider than the distance between the propodeal spine tips) than in T. grandinode (in which the petiole node is ca. 1.4–1.5 times wider than the distance between the propodeal spine tips). From Tetramorium lerouxi, the only other glabrous species with the petiole node distinctly laterally expanded, T. nama can be readily distinguished by the sculpture of the dorsal mesosoma and petiole segments as indicated in the key. T. nama shares similar head, mesosoma, petiole and postpetiole sculpture with Tetramorium duncani, but can be distinguished from this species as the former has substantially longer propodeal spines (PSLI2 23–25 vs. 12–17) a much shorter petiole node (LPeI 66–70 vs. 78–96), a distinct subpetiolar process (which T. duncani lacks) and a much less pronounced sub-postpetiolar process (very well-developed in T. duncani).

Distribution based on Regional Taxon Lists
Afrotropical Region: South Africa.

Habitat
Riverine fringe showing living vegetation dominated by Euclea pseudebenus as well as numerous cut Prosopis glandulosa (freshly cut and piles of dry branches). It is known only from a single collection of eight workers from one pitfall trap, which was situated in an area transitional between Lower Gariep Alluvial Vegetation and Noms Mountain Desert (Mucina and Rutherford, 2006). The pitfall trap transect was located in open vegetation between closed thicket on the banks of the Orange River and alluvial terrace gravels further from the river. The site is located in the extreme north of the RNP in the Namakwa district of the Northern Cape, South Africa; more extensive surveys in the surrounding region are required to determine the extent of occurrence of the species.

Biology
This species is only know from a single collection of eight workers captured in a pitfall trap. Few facts can be gleaned from the type series regarding this ant's biology. . . but what is known allows some opportunity for speculation.

The morphology of T. nama places it in the solidum species-group, which is a group of seed harvesting ants. It therefore seems likely Tetramorium nama is a seed harvester and possesses traits associated with their diet that can explain how they are able to inhabit what is generally a harsh environment for ants. Seed harvesters can capitalize on the sporadic but often prolific seed production that typically occurs in open, low plant-biomass, arid habitat. Forages can collect a huge number of seeds and create large seed reserves within the nest. This can be a vital food resource for colonies that live in an environment that almost always features a dearth of seeds and insects they could potentially scavenge upon.

Based on other sampling conducted in and around the type locality, T. nama appears to be rare and is likely to have a relatively small range. If so, it faces more threats than just the demographic challenges that arise for any species with a small population size and a specialized lifestyle. Tetramorium nama also occurs in an area where mining, grazing and an invasive tree species are degrading the local environment and climate change has the potential to push the already hot and dry local conditions to new extremes.

Nomenclature

 * . Tetramorium nama Hawkes 2020: 59, figs. 1A-C, 2A, 3 (w.) SOUTH AFRICA.

Worker
Holotype CASENT0818990: HL 1.21, HL2 1.17, HW 1.10, SL 0.85, EL 0.31, PH 0.56, PW 0.74, WL 1.32, PSL 0.28, PTH 0.42, PTL 0.29, PTW 0.43, PPH 0.42, PPL 0.29, PPW 0.56. Indices: CI 91, CI2 94, DMI 56, DPeI 147, DPpI 191, OI 28, SI 77, LMI 42, PSLI 23, PSLI2 24, PeNI 58, LPeI 70), LPpI 69, PpNI 76, PPI 130 (all measurements in mm, indices as percentage).

Paratypes (6 measured, mean including holotype in parentheses): HL 1.14–1.22 (1.19), HL2 1.11–1.19 (1.15), HW 1.04–1.13 (1.09), SL 0.80–0.86 (0.83), EL 0.30–0.33 (0.32), PH 0.54–0.56 (0.55), PW 0.68–0.75 (0.73), WL 1.17–1.32 (1.24), PSL 0.26–0.29 (0.27), PTH 0.38–0.43 (0.41), PTL 0.27–0.29 (0.28), PTW 0.39–0.44 (0.42), PPH 0.39–0.43 (0.42), PPL 0.26–0.29 (0.28), PPW 0.49–0.56 (0.53). Indices: CI 90–93 (92), CI2 94–96 (95), DMI 58–60 (59), DPeI 148–158 (152), DPpI 184–201 (194), OI 28–30 (29), SI 74–77 (76), LMI 44–46 (44), PSLI 22–24 (23), PSLI2 23–25 (24), PeNI 56–60 (58), LPeI 66–70 (68), LPpI 64–69 (66), PpNI 71–75 (73), PPI 124–127 (126) (all measurements in mm, indices as percentage)

Head a little longer than wide (CI 92), posterior margin shallowly indented medially, sides slightly convex, rounding posteriorly into the broadly convex occipital corners. Clypeus with a distinct but shallow medial indentation and ca. 10–12 longitudinal costulae overlain on a very effaced shagreenate ground sculpture, the surface between the costulae almost smooth, moderately shining. Frontal carinae fading out behind the frontal lobes and merging with the remaining cephalic sculpture from the level of the anterior margin of the eyes, often broken behind this point, but occasionally fairly long and reaching to midway between the level of the posterior margin of the eyes and the occipital margin. Eyes large, situated at approximately the mid-length of the sides of the head and with 16–17 ommatidia in the longest row, ocelli absent. Mandibles weakly longitudinally rugose, with seven teeth. Psammophore well-developed, comprising a row of ca. 10–14 elongate J-shaped hairs on the ventral surface of the head behind the posterior margin of the buccal cavity, two rows of ca. five hairs each along the distal inner and outer ventral margins of each mandible and a cluster of four or five hairs proximally on the ventral mandibular margins. Antennal scapes short, stout, basally curved and distally thickened; when laid back, scapes fall short of the posterior margin of the head by ca. one-fifth of their length. Scapes with strong appressed pubescence, lacking erect setae, remaining antennal segments with sub-appressed pubescence. Scapes weakly longitudinally carinulate, the remaining antennal segments smooth and shining, unsculptured except for piligerous punctures. Dorsal surface of head with dense longitudinal costulae, ca. 22 between the frontal carinae at the level of the mid-point of the eyes; costulae approximately parallel medially but diverging posterolaterally toward the occipital corners, behind which they reflex and continue anterad on the lateral surface of the head, a few above, but most below the eyes. Spaces between the costulae shiny and almost smooth, with faint reticulate/shagreenate sculpture.

Mesosoma laterally with irregular longitudinal costulae overlaid on a weak reticulate- punctate ground sculpture, anterodorsally with one continuous and several broken transverse marginal costulae; dorsally with effaced reticulate-punctate ground sculpture overlain by fairly uniform longitudinal costulae that continue running approximately parallel all the way to the pronotal margin, where they either fade out or join approximately at right angles with one of the transverse components. Propodeal spiracles round, situated slightly above the mid-height of the sides of the propodeum. Propodeal spines long and acute (PSLI 22–24). Declivity dorsally shallowly concave in dorsal view but straight ventrally. Ground sculpture of propodeum shagreenate to reticulate-punctate, overlain by costulae which are longitudinal on the dorsal face but transverse on the declivitous face and between the bases of the propodeal spines. Propodeal lobes broadly rounded.

Petiole node in dorsal view subtrapezoidal, distinctly wider behind than in front and distinctly wider than long, in profile with a broadly rounded anterodorsal margin and an acute, slightly overhanging posterodorsal margin. Subpetiolar process a narrow lamella subtended by a short but distinct anteriorly orientated tooth. Dorsal surface of node usually with several irregular roughly concentric or whorled costulae, in some specimens the costulae are irregularly transverse.

Postpetiole node distinctly broader than the petiole node in dorsal view, with irregular, slightly recurved transverse costulae over the entire dorsal surface, the anterior face of the node slightly concave, the posterior face slightly convex.

Gaster with dense but fine basigastral costulae radiating over the anterior third of the first tergite, overlain on a dense shagreenate ground sculpture which weakens posteriorly. Sting present, weakly curved ventrad, with a distinct pennant-shaped lamellate appendage.

Legs with fairly uniform shagreenate sculpture throughout.

Pilosity: two pairs of erect setae are present on the dorsal surface of the head behind the frontal lobes; one about level with the anterior margin of the eyes and one close to the occipital corners. Standing hairs are absent from all dorsal surfaces of the mesosoma, petiole segments, the first and usually the second gastral segment (the latter occasionally with one to two pairs of very short suberect setae). Dorsal surfaces of head, petiole, postpetiole and gaster with scattered appressed pubescence, which is very sparse, reduced in length and appearing virtually absent from the dorsal mesosoma. Femora and tibiae with appressed to sub-appressed pubescence on all surfaces. Gastral sternites with appressed pubescence and long erect setae, which on the first sternite are concentrated medially and posteriorly.

Colour mainly dark blackish brown, the mandibles a distinctly contrasting reddish brown; antennae, legs and peduncle of petiole similar to the mandibles but with the median portions of the femora and tibiae darker and similar to the body colour.

The type series is very consistent in overall appearance and colour, but there is some variation in the pattern of sculpture on the petiole node as indicated above. Worker measurements and proportions are quite consistent with measurement ranges 4–13% and index ranges 2–9% of their mean values.

Type Material

 * Holotype. South Africa • 1worker; Northern Cape Province, Namakwa, Richtersveld National Park; 28.05795S, 17.11256E ±100 m; alt. 65 ±10 m.a.s.l.; P.G. Hawkes, D. Molenaar, R.N. Ungerer leg.; 12–18 Sep. 2019; Collection number: ODM2019-T8-1; Pitfall trap; Point-mounted; SAMC CASENT0818990.
 * Paratypes. South Africa • 6 workers; same data as for holotype; Point-mounted; AFRC CASENT0818735, CASENT0818736, BMNH CASENT0818992, CASC CASENT0818993, CASENT0818994, SAMC CASENT0818991; • 1 worker; same data as for holotype; 95% ethanol; AFRC CASENT0819639.

Etymology
Nama refers to the local Nama people who, together with SANParks, jointly manage the Richtersveld National Park. The specific epithet is a noun in apposition and is thus invariant.