Pogonomyrmex cunicularius

A South American seed harvesting ant found in arid habitats.

Identification
Johnson (2015) - Worker Within the P. cunicularius-group, the combination of: (1) in profile, petiolar node broadly rounded, (2) inferior propodeal spines rounded, (3) superior propodeal spines moderately long, shorter than distance between their bases, and (4) first gastral tergum smooth and strongly shining uniquely characterize this species.

Male This caste is diagnosed by: (1) first gastral tergum lacking striae, (2) femur long (HFL > 1.95 mm), HFI > 150.0, (3) head weakly elongate (CI < 100.0), (4) posterior surface of petiolar node rugose to rugoreticulate, (5) in profile, petiolar node rounded, (6) superior propodeal spines consist of teeth to short spines, and (7) notauli present.

Pogonomyrmex cunicularius is not known to co-occur with any other P. cunicularius-group species but additional collections may show it co-occurs with both Pogonomyrmex pencosensis and Pogonomyrmex serpens. Pogonomyrmex cunicularius can be distinguished from these two species based on the following characters: (1) in profile, petiolar node broadly rounded, (2) inferior propodeal spines rounded, and (3) first gastral tergum smooth and strongly shining. In P. pencosensis and P. serpens: (1) in profile, the petiolar node is angulate, (2) inferior propodeal spines are acuminate, and (3) first gastral tergum is weakly to moderately coriarious, dull to weakly shining.

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Uruguay.

Habitat
Pogonomyrmex cunicularius is a lowland species that occurs at elevations from 20–90 m. This species is only known to occur east and north of Río Paraná in the Espinal, Uruguayan Savanna, and Humid Pampas ecoregions as defined by Olson et al. (2001). The very wide Río Paraná may act as a barrier to dispersal by ergatoid queens. At present, P. cunicularius appears to be rare with very fragmented populations that likely result from intense and widespread agricultural use over most of its historic range. (Johnson 2015)

Biology
This ant was found to be an important seed disperser of Jatropha excisa seeds by Aranda-Rickert and Fracchia (2011). As part of their field study, in the Monte Desert biome of northern Argentina, they found that nests of Pogonomyrmex cunicularius were ~ 60 cm deep with an average of 13 chambers. The entrance to the soil nest were surrounded by a characteristic 20-cm diameter disk made of course soil particles. Worker number per nest averaged around 600 workers (n=6).

Pogonomyrmex cunicularius foraging behavior has also been studied (Aranda-Rickert and Fracchia 2012). This ant is a subordinate species with solitary foragers. They will typically abandon baits when challenged by other ants but also employ an opportunistic robbing behaviour: "when a bait was being monopolized by other species, the ant rapidly took a piece of food while avoiding the other species attack and then returned with the prey to the nest." These ants are highly thermophilic. They are active outside the nest during the warmest part of the day, when soil temperatures can reach as high as 61C.

Johnson (2015) - This species is a solitary forager that can travel >25 m from the nest. Nests of P. cunicularius usually have a pebble tumulus up to 25 cm in diameter with a nest entrance that is up to 2–3 cm in diameter. Colonies of P. cunicularius probably contain 500 to >1000 workers, and they can produce >100 ergatoid queens and numerous males (pers. obs.).

Sexuals have been collected from nests from 13 December to 13 February, and one founding queen was excavated on 17 February, indicating the mating flights occur during the austral summer. The large number of ergatoid queens produced by colonies (>100) infers that queens use independent colony founding (see Peeters et al., 2012), which is an unusual behavior for ergatoid queens (see Johnson, 2010). One excavated queen was haplometrotic, and founding queens are probably semi-claustral (they forage) (see Johnson, 2010). Queens contained 9–12 ovarioles (n = 3), compared to four in workers (n = 6).

Nomenclature

 *  cunicularius. Pogonomyrmex cunicularius Mayr, 1887: 613 (w.m.) ARGENTINA. [Misspelled as cunicularis by Santschi, 1922b: 349 and some subsequent authors.] Senior synonym of brevispinus: Johnson, 2015: 37.
 * brevispinus. Pogonomyrmex cunicularis var. brevispinus Santschi, 1931e: 275 (w. ergatoid q.m.) ARGENTINA. Junior synonym of cunicularius: Kusnezov, 1951a: 251; Johnson, 2015: 37.

Worker
Johnson (2015) - Lectotype (n = 16). HL 2.38 (1.85–2.47); HW 2.07 (1.52–2.10); MOD 0.38 (0.31–0.42); OMD 0.62 (0.45–0.69); SL 1.55 (1.44–1.92); PNW 1.44 (1.04–1.47); HFL 2.57 (2.09–2.68); ML 2.83 (2.05–2.87); PW 0.50 (0.40–0.54); PPW 0.72 (0.55–0.76). Indices: SI 74.88 (79.40–100.00); CI 86.97 (81.01–88.21); OI 18.36 (17.79–21.16); HFI 124.15 (119.23–139.38).

Head elongate (CI = 81.01–88.21), widest immediately posterior to mandibles, narrowing posterior to eyes; posterior margin flat to weakly convex in full-face view. Cephalic dorsum with weak to moderately strong, wavy or irregular longitudinal rugae to weakly rugoreticulate, rugae often weaker to indistinct near posterior margin; in full-face view, medial rugae diverging weakly toward posterior corners of head. Cephalic interrugae weakly to moderately granulate, weakly shining. Vertex weakly rugose to weakly to moderately granulate, dull to weakly shining. Anterior margin of clypeus flat to weakly convex; dorsal surface with at least several subparallel longitudinal or oblique rugae. Mandibles with six teeth; mandibular dorsum coarsely rugose. Eyes small, MOD ranging from 0.15–0.18x HL. In profile, eyes situated anterior to middle of head, OMD = 1.36– 1.77x MOD. Antennal scapes long (SI = 74.88–100.00), surpassing vertex by less than length of first funicular segment; entire scape with longitudinal striae. Basal flange of scape well-developed with carinate margin. Psammophore poorly-developed, consisting of short to medium-length hairs scattered across ventral surface of head.

Promesonotal profile moderately convex, propodeum flat; all mesosomal surfaces with subparallel, irregular rugae to weakly rugoreticulate. In dorsal view, humeral shoulders of pronotum rounded. Dorsum of promesonotum and sides of pronotum with transverse, oblique to longitudinal, irregular rugae to rugoreticulate; mesopleura with irregular rugae that angle posterodorsally. Superior propodeal spines moderately long, acuminate, shorter than distance between their bases; spines connected by well-defined keel; wavy to irregular transverse rugae on propodeal dorsum traverse ventrally or anteroventrally on sides. Inferior propodeal spines well-developed, triangular, wider than high, tips broadly rounded to bluntly angulate. Propodeal spiracles narrowly ovate facing posterad. Interrugae on mesosoma smooth to weakly granulate, weakly to strongly shining. Legs long (HFL = 2.09–2.68 mm), weakly to moderately coriarious to granulate, dull to weakly shining. Peduncle of petiole about 0.8x length of petiolar node, anteroventral margin with bluntly angulate to angulate triangular process. In profile, posterior surface of petiolar node flattened; node asymmetrical with anterior surface shorter than posterior surface, apex broadly rounded. In dorsal view, petiolar node about 1.5x longer than wide, widest near anterior margin. Sides and posterior surface of petiolar node with weak to moderately coarse, irregular, transverse rugae, or granulate-punctate. Dorsum of postpetiole convex in profile; in dorsal view, widest near posterior margin, narrowing to anterior margin, maximum width about equal to length, strongly granulate-punctate, dull to weakly shining. First gastral tergum smooth, strongly shining.

Erect to semi-erect yellowish pilosity moderately abundant on head, variable in length, longest hairs approaching MOD. Moderately abundant suberect yellowish pilosity on scape; abundant decumbent hairs on funicular segments. Legs with moderately abundant subdecumbent to decumbent yellowish setae. Mesosoma, petiolar node, postpetiole, and gastral terga with moderately dense erect setae, mostly similar in length, longest hairs not exceeding MOD. Body concolorous tannish-orange to tannish-red.

Queen
Johnson (2015) - (n = 12). HL 2.26–2.66; HW 1.96–2.38; MOD 0.35–0.45; OMD 0.54–0.66; SL 1.53–1.87; PNW 1.23–1.60; HFL 2.27–2.70; ML 2.46–3.20; PW 0.51–0.67; PPW 0.71–0.93. Indices: SI 74.63–87.24; CI 85.38–90.49; OI 17.07–20.74; HFI 111.34–125.37.

Male
Johnson (2015) - (n = 12). HL 1.30–1.77; HW 1.17–1.54; MOD 0.51–0.64; OMD 0.21–0.32; SL 0.38–0.49; HFL 1.98–2.48; ML 2.51–3.25; PW 0.48–0.67; PPW 0.63–0.97. Indices: SI 24.84–35.66; CI 82.89–92.81; OI 39.61–47.86; HFI 154.69–182.05.

Type Material
Syntypes of P. cunicularius: 3 workers [MSNG], 2 workers [NMW], URUGUAY, no location; 1 male [NMW], URUGUAY, Montevideo: Montevideo; 2 workers [NMW], ARGENTINA, Buenos Aires (Prof. Berg leg.). NMW worker from URUGUAY designated LECTOTYPE [CASENT0173372] by Johnson, 2015: 44.

Syntypes of P. brevispinus: 1 worker, 1 ergatoid queen [MACN], ARGENTINA, Entre Ríos: Estación Sosa (Mac Donagh leg.). MACN worker designated LECTOTYPE [CASENT0249048] by Johnson, 2015: 44.

Etymology
Johnson (2015) - The specific epithet, cunicularius, (from Latin cunicul-, which indicates a miner or burrower, plus the Latin suffix -arius, which denotes belonging to) apparently refers to the soil nests excavated by this species. Mayr did not discuss the naming of this species, but Kusnezov (1949) wrote that P. cunicularius was the only Argentinian species of Pogonomyrmex that constructed a nest crater.