Pogonomyrmex apterogenos, Johnson, 2021

Johnson, Robert A., 2021, A taxonomic revision of South American species of the seed-harvester ant genus Pogonomyrmex (Hymenoptera: Formicidae). Part II, Zootaxa 5033 (1), pp. 1-230 : 31-39

Pogonomyrmex apterogenos NEW SPECIES

( Figures 1E–F , 10A , 11–13 )

Distribution— Figure 14A

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) .

Worker diagnosis. 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, and (5) head ferruginous orange, dorsum of promesonotum concolorous orangish-black, rest of mesosoma blackish-orange to blackish ( Figures 10A , 11 ).

Measurements — holotype (n = 13 paratypes). HL 1.64 (1.53–1.82); HW 1.68 (1.43–1.79); MOD 0.39 (0.34– 0.41); OMD 0.39 (0.34–0.44); SL 1.33 (1.07–1.36); PNW 1.09 (0.94–1.16); HFL 1.75 (1.35–1.83); ML 1.93 (1.61– 2.02); PW 0.41 (0.35–0.44); PPW 0.56 (0.48–0.60). Indices: SI 79.17 (68.94–83.22); CI 102.44 (93.46–102.53); OI 23.21 (21.43–25.00); HFI 104.17 (88.27–104.27).

Description. Head quadrate to longer than wide (CI = 93.46–102.53); posterior margin flat in full-face view. Longitudinal rugae on cephalic dorsum prominent, 1–2 pairs of medial rugae meet and end at posterior margin of frontal triangle, rugae between frontal lobes weakly converging. Interrugae on cephalic dorsum moderately to strongly granulate-punctate, dull to weakly shining; posterior corners rugose, interrugae weakly granulate, weakly shining to smooth and shining. Anterior margin of clypeus moderately concave, dorsum with numerous subparallel, longitudinal rugae. Numerous long, curved, bristle-like, yellowish macrochaetae project from anterior margin of clypeus and basolateral margin of mandibles. Mandibles with six teeth; mandibular dorsum coarsely rugose. MOD ranging from 0.21–0.25× HL. In profile, eyes situated slightly anterior to middle of head, OMD = 0.92–1.15× MOD. In full-face view, eyes protruding slightly beyond lateral margins of head. Antennal scapes (SI = 68.94–83.22) failing to reach posterior corners of head by less than to about the length of basal funicular segment. Antennal scapes usually weakly striate, interstriae weakly to moderately granulate, weakly shining to smooth and shining; basal flange well developed with carinate margin. Psammophore well developed.

Mesosomal profile flat to weakly convex; all mesosomal surfaces with prominent widely spaced, regular, subparallel-parallel rugae. 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 that continue onto pronotal sides. In dorsal view, humeral shoulders of pronotum enlarged, dorsolateral margin strongly angulate. Promesonotal suture usually present. Regular to weakly irregular rugae on mesopleura angle posterodorsally; regular transverse rugae on dorsum of propodeum traverse anteroventrally on sides. Superior propodeal spines consist of acuminate denticles, small triangular teeth, or rarely short spines, length rarely more than width at base, spines usually connected by well defined keel. Inferior propodeal spines wider than high, triangular, tip broadly rounded to acuminate, height similar to or slightly greater than length of superior spines. Propodeal spiracles narrowly ovate facing posterad. Interrugae on mesosoma moderately to densely granulate, dull to weakly shining. Legs moderately coriarious, weakly shining to smooth and shining.

Peduncle of petiole about as long as petiolar node, anteroventral margin with a weak to well developed, broadly rounded process. In profile, posterior surface of petiolar node weakly convex; petiolar node asymmetrical with anterior surface notably shorter than posterior surface, apex subangulate to angulate. In dorsal view, petiolar node longer than wide, sides subparallel anterad, slightly narrower posterad, anterior margin broadly rounded. Sides and posterior surface of petiolar node with regular transverse rugae. Dorsum of postpetiole convex in profile; in dorsal view, widest near posterior margin, narrowing anterad, width and length similar; transverse to weakly arcuate rugae posterad, anterad rugae traversing medially from lateral margin then curving anterad to become longitudinal; anterolateral rugae concentric, curving from lateral to anterior margin, or rarely with all anterad rugae transverse or weakly arcuate; rugae on dorsum of postpetiole finer, denser than those on posterior surface of petiolar node; interrugae on both surfaces weakly granulate, weakly shining to smooth and strongly shining. Striae extend over more than anterior one-half of first gastral tergum, often extending to posterior margin or posterior margin moderately to strongly coriarious, dull to weakly shining; posterolateral margins smooth and shining to moderately coriarious, weakly shining.

Erect, mostly short to medium length, yellowish pilosity moderately abundant on head, no hairs exceed about 0.7× MOD. Moderately abundant suberect to semidecumbent pilosity on scape; abundant decumbent hairs on funicular segments. Legs with moderately abundant suberect to decumbent, yellowish setae. Rest of body with moderately dense, erect, medium-length, yellowish setae. Head dark ferruginous orange to dark red-orange; mandibles, antennae, clypeus, frontal lobes, anterior margin of head black; dorsum of promesonotum orangish-black; rest of mesosoma dark orangish-black, blackish, or black; gastral terga very dark orange-black ( Figures 10A , 11 ).

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, and (4) in dorsal view, pronotum and mesoscutum weakly differentiated, longitudinal rugae on mesoscutum continue longitudinally or obliquely onto pronotum ( Figures 1E–F , 12 ).

Measurements —(n = 6). HL 1.83–1.96; HW 1.84–1.94; MOD 0.43–0.48; OMD 0.43–0.51; SL 1.25–1.42; PNW 1.14–1.25; HFL 1.52–1.95; ML 2.08–2.30; PW 0.47–0.50; PPW 0.57–0.75. Indices: SI 66.67–77.17; CI 95.92–103.28; OI 22.75–25.54; HFI 82.61–103.26.

Description. Ergatoid; in full-face view, head quadrate to subquadrate (CI = 95.92–103.28), posterior margin flat. Longitudinal rugae on cephalic dorsum wavy, medial rugae not diverging toward posterior corners along posterior margin; rugae between frontal lobes weakly converging, 1–2 pairs of medial rugae meet and end at posterior margin of frontal triangle. Posterior corners rugose; interrugae on cephalic dorsum and posterior corners moderately granulate-punctate, dull to weakly shining. Mandibles with six teeth, dorsal surface coarsely rugose. Psammophore well developed.

Mesosoma lacking morphological structures related to or for inserting wings; all mesosomal surfaces with subparallel, wavy rugae; interrugae smooth and shining to moderately granulate-punctate, weakly shining. Pronotum large with longitudinal or oblique rugae that continue from mesoscutum and traverse ventrally on pronotal sides, anterior margin occasionally with transverse rugae. Mesoscutum reduced in size, not extending to pronotal collar; sides subparallel, converging to bluntly acuminate, arcuate anterior margin. Dorsum of propodeum transversely rugose; superior propodeal spines reduced to small teeth; inferior propodeal spines triangular, longer than superior spines, tips acuminate. Peduncle of petiole long, anteroventral margin with a weakly developed rounded process. In profile, petiolar node asymmetrical with anterior surface notably shorter than posterior surface, apex angulate. Postpetiole convex in profile; in dorsal view, maximum width about equal to length. Posterior surface of petiolar node and dorsum of postpetiole with wavy transverse rugae; interrugae weakly punctate, weakly shining to shining. Striae extend over more than anterior one-half of first gastral tergum, often extending to posterior margin or posterior margin moderately to strongly coriarious, weakly shining to dull; posterolateral margins smooth and shining to moderately coriarious, weakly shining. Most body surfaces with moderately abundant suberect to erect, short, white to cream-colored setae, longest hairs on posterior terga. Head ferruginous orange; pronotum, mesoscutum, first gastral tergum blackish-orange; rest of body blackish to black, sometimes with a weak orangish infusion ( Figures 1E–F , 12 ).

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, and (3) notauli absent ( Figure 13 ).

Measurements —(n = 8 + 2 paratypes). HL 1.35–1.60; HW 1.35–1.64; MOD 0.42–0.48; OMD 0.21–0.31; SL 0.54–0.61; HFL 1.52–1.70; ML 1.84–2.20; PW 0.42–0.49; PPW 0.57–0.66. Indices: SI 34.76–42.22; CI 92.47– 106.34; OI 29.14–33.10; HFI 103.40–118.52.

Additional material examined. ARGENTINA: Catamarca: Rt 45 at 28.4 km S Cortaderas, 10,170’, Jan 28, 2010 ( RAJC) ; Rt 45 at 13.7 km S Cortaderas, 10,900’, Jan 5, 2006 ( MCZC; RAJC) ; Rt 45 at 1.4 km N Cortaderas, 11,070’, Jan 9, 2010 ( RAJC) ; Rt 45 at 20.5 km N Cortaderas, 11,090’, Jan 5, 2010 ( CASC; MCZC; RAJC; UCDC) ; Rt 45 at 30.5 km E Chile border, 13,330’, Jan 30, 2010 ( RAJC) ; Rt 60 at 0.5 km E La Gruta, 13,300’, Mar 20, 2017 ( RAJC) ( Figure 14A ).

Etymology. The specific epithet, apterogenos (Latin, aptero = wingless, and genos = parentage), refers to this species having ergatoid queens and males.

Discussion. Pogonomyrmex apterogenos is not known to co-occur with any congeners. However, P. apterogenos is similar to P. lagunabravensis , P. longibarbis , and P. 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 P. 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.

Biology. 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.

Pogonomyrmex apterogenos , along with its sister species, P. 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.

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) ( Figure 14A ).

Figures

FIGURE 1. Closeup photographs in dorsal view and in profile showing the diversity of mesosomal morphologies for ergatoid queens of Pogonomyrmex: (A–B) P. pencosensis (CASENT0869790), (C–D) P. apterogenos (CASENT0869791), (E–F) P. laticeps (CASENT0217266), (G–H) P. cunicularius (CASENT0173109), and (I–J) P. naegelii (CASENT0869793). Photographs by Robert Johnson and Erin Prado from www.AntWeb.org.

FIGURE 10. Closeup photographs for workers of Pogonomyrmex showing dorsum of promesonotum with rugae that are 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: (A) P. apterogenos holotype worker (CASENT0914124), (B) P. lagunabravensis holotype worker (CASENT0249051), (C) P. longibarbis (CASENT0249056), and (D) P. sanmartini (CASENT0922481), and dorsum of promesonotum with rugae that are usually wavy to irregular, discontinuous or with short lateral branches; rugae on mesonotum mostly longitudinal but often becoming irregular to rugoreticulate on pronotum; anterodorsal margin of pronotum with wavy to irregular rugae to rugoreticulate, usually with short lateral branches: (E) P. RAJ-altip worker (CASENT0235280), (F) P. andinus (CASENT0914130), (G) P. tafi holotype worker (CASENT0235307), and (H) P. sanmartini (CASENT0922479). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 11. Photographs of Pogonomyrmex apterogenos holotype worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0914124). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 12. Photographs of Pogonomyrmex apterogenos ergatoid queen: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0173116). Photographs by April Nobile from www.AntWeb.org.

FIGURE 13. Photographs of Pogonomyrmex apterogenos ergatoid male: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0173117). Photographs by April Nobile from www.AntWeb.org.

FIGURE 14. Geographic distribution of: (A) Pogonomyrmex apterogenos, (B) P. araucania, and (C) P. atacama. The large black circle in each panel denotes the type locality.