Pogonomyrmex apterogenos

Little is known about the biology of P. apterogenos. Nests from the type series were in very sparsely vegetated Puna Desert habitat that consisted of scattered Chuquiraga atacamensis (Asteraceae) and occasional individuals of Atriplex sp. (Amaranthaceae). At another location in this same valley (near 4000 m), workers foraged solitarily for seeds on an Adesmia sp. (Fabaceae). Nests were relatively difficult to locate at this site, but workers were easy to locate on these plants and follow back to their nest. This species, as well as Pogonomyrmex lagunabravensis, are the only known ant species in which both sexual castes are ergatoid.

Identification
Workers of this species are uniquely characterized by the following combination of features:
 * 1) striae extend over more than anterior one-half of first gastral tergum, posterolateral margins smooth and shining to moderately coriarious, weakly shining
 * 2) for most to all workers in a series, rugae on dorsum of promesonotum well defined, very regular and continuous, lacking short lateral branches; longitudinal rugae on mesonotum diverging toward humeral shoulders of pronotum; anterodorsal margin of pronotum with one to several straight, strong, continuous, transverse rugae
 * 3) superior propodeal spines consist of tubercles, denticles, or teeth, rarely short spines
 * 4) rugae between frontal lobes weakly converging, 1–2 pairs of medial rugae meet and end at posterior margin of frontal triangle
 * 5) head ferruginous orange, dorsum of promesonotum concolorous orangish-black, rest of mesosoma blackish-orange to blackish (Figures 10A, 11).

Pogonomyrmex apterogenos is not known to co-occur with any congeners. However, P. apterogenos is similar to Pogonomyrmex lagunabravensis, Pogonomyrmex longibarbis, and Pogonomyrmex pulchellus; all four species inhabit high elevations (> 3000 m), striae extend over more than anterior one-half of first gastral tergum, and longitudinal rugae on promesonotum are very regular, subparallel-parallel, with several continuous, transverse rugae along the anterior margin of the pronotum (Figure 10). Pogonomyrmex apterogenos can be distinguished from all three species based on the 1–2 most medial rugae on the cephalic dorsum converging and ending near the posterior margin of the clypeus, and rugae between the frontal lobes weakly converging. In P. lagunabravensis, P. longibarbis, and P. pulchellus, the 1–2 most medial rugae on the cephalic dorsum are subparallel-parallel and typically continue onto the clypeus rather than ending near the posterior margin of the clypeus. Pogonomyrmex apterogenos might also be confused with Pogonomyrmex rastratus, but the superior propodeal spines of P. apterogenos usually consist of acuminate denticles or small triangular teeth with length of the inferior propodeal spines similar to or longer than the superior spines. In P. rastratus, the superior propodeal spines are short to long, usually long in some workers in a series, and the inferior propodeal spines are shorter than the superior spines.

Queen diagnosis. Queens of this species are diagnosed by the following combination of features:
 * 1) ergatoid
 * 2) first gastral tergum with striae
 * 3) anterior margin of clypeus entire
 * 4) in dorsal view, pronotum and mesoscutum weakly differentiated, longitudinal rugae on mesoscutum continue longitudinally or obliquely onto pronotum

Male diagnosis. Males of this species are diagnosed by the following combination of features
 * 1) ergatoid
 * 2) in profile, cephalic rugae posterior to eyes continue more or less directly to posterior corners, not forming circumocular whorls and not converging posterior to eyes
 * 3) notauli absent

Distribution
Pogonomyrmex apterogenos inhabits elevations from 3080–4040 m. This species occurs in the Central Andean puna and Southern Andean steppe ecoregions, as defined by Olson et al. (2001).

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina.

Biology
Pogonomyrmex apterogenos, along with its sister species, Pogonomyrmex lagunabravensis, appear to be unique among ants in that both queens and males are ergatoid. Little is known about the mating system of either species. Males were collected from 5–30 January, and one ergatoid queen was collected under a rock on March 20, indicating that the ergatoid queens of this species found nests independently. The larger size of queens makes them relatively easy to differentiate from workers, but males and workers are similar in size and color such that caste must be verified using a hand lens or microscope. It is unknown if males continue to produce sperm throughout their life, as occurs in ergatoid males of some species of Cardiocondyla (see Heinze & Hölldobler, 1993). Partly excavated nests suggested that colonies are diffuse, with tunnels radiating in all directions. These partial excavations indicated that colonies probably contain from 500 to more than 1000 workers.

Nomenclature

 * . Pogonomyrmex apterogenos Johnson, 2021: 31, figs. 1E-F, 10A, 11-13, 14A (w.eq.em.) ARGENTINA (Catamarca).

Type Material

 * Holotype worker [MACN: CASENT0914124]: ARGENTINA, Catamarca Province: Departamento Tinogasta, Chuschuil Valley at 20.9 km S Cortaderas, 27º44.0’S 68º08.2’W, 10,380’ (3145 m), 31 January 2010 (R.A. Johnson #4376).
 * Paratypes, same data as holotype: IFML (6 workers), MACN (24 workers), LACM (6 workers), MCZC (9 workers), RAJC (21 workers), UCDC (3 workers), USNM (3 workers).
 * Additional paratype series from the same locality and date—RAJ #4377: MACN (6 workers), RAJC (6 workers); RAJ #4378: MACN (12 workers), RAJC (11 workers, 1 ergatoid male): RAJ #4379: IFML (6 workers), MACN (9 workers), RAJC (12 workers); RAJ #4380: IFML (3 workers), MACN (9 workers), RAJC (11 workers, 1 ergatoid male).