Pogonomyrmex propinqua, 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 : 143-149

Pogonomyrmex propinqua NEW SPECIES

( Figures 69–71 )

Distribution—68B

Pogonomyrmex rastratus Mayr : Claver & Fowler, 1993; Pirk, et al., 2004; Pirk & Lopez de Casenave, 2006; Pirk, et al., 2007; Pol & Lopez de Casenave, 2004; Pirk et al., 2009; Pirk & Lopez de Casenave, 2010; Pol, et al., 2011; Pirk & Lopez de Casanave, 2011; Nobua Behrmann et al., 2010; Nobua-Behrmann et al., 2013. Misidentifications.

Holotype worker [ MACN: CASENT0922160 ]: ARGENTINA, Mendoza: Departamento Santa Rosa, Rt 7 at 13.9 km E La Dormida, 33 o 23.8’S 67 o 46.8’W, 1760’ (535 m), 11 April 2015 (R.A. Johnson #5463) . Paratypes, same data as holotype: IFML (6w) , LACM (9w) , MACN (12w), MCZ (9w), RAJC (33w), UCDC (3w), USNM (9w).

Worker diagnosis. Workers of this species are uniquely characterized by the following combination of features: (1) striae extend over anterior one-half or more of first gastral tergum; posterolateral margins moderately to strongly coriarious, weakly shining to dull, (2) head and gaster ferruginous orange; mesosoma black, dorsum of promesonotum often with orangish infusion to orangish-black, (5) dorsum of mesonotum with irregular longitudinal rugae to rugoreticulate-vermiculate, lateral branches usually connect adjacent rugae, (6) promesonotal suture usually present, (7) superior propodeal spines long, length> 0.6× the distance between their bases, (8) inferior propodeal spines well developed, height usually greater than that of superior spines, (9) most hairs on anterior half of first gastral tergum <0.16 mm long, and (9) only known from San Luis and Mendoza Provinces ( Figure 69 ).

Measurements — holotype (n = 13). HL 1.94 (1.68–2.08); HW 2.03 (1.79–2.32); MOD 0.39 (0.32–0.44); OMD 0.47 (0.41–0.53); SL 1.32 (1.11–1.46); PNW 1.27 (1.13–1.39); HFL 1.66 (1.50–1.91); ML 2.10 (1.89–2.27); PW 0.53 (0.42–0.57); PPW 0.70 (0.59–0.76). Indices: SI 65.02 (58.88–69.23); CI 104.64 (104.06–115.00); OI 19.21 (16.96–20.33); HFI 81.77 (80.65–94.97).

Description. Head subquadrate to wider than long (CI = 104.06–115.00), widest just posterior to eyes; posterior margin flat in full-face view. Longitudinal rugae on cephalic dorsum prominent; in full-face view, medial rugae weakly diverging toward posterior corners of head. Interrugae on cephalic dorsum strongly granulate, dull. Posterior corners rugose, interrugae weakly to strongly granulate, dull to weakly shining. Anterior margin of clypeus strongly concave, dorsum with numerous subparallel, longitudinal rugae. Numerous long, curved, bristle-like, cream to light yellowish hairs project from anterior margin of clypeus and basolateral margin of mandibles. Mandibles with six teeth; mandibular dorsum coarsely rugose. MOD ranging from 0.20–0.24× HL. Eyes in profile situated slightly anterior to middle of head, OMD = 1.1–1.5× MOD. In full-face view, eyes not protruding to protruding slightly beyond lateral margins of head. Antennal scapes (SI = 58.88–69.23) failing to reach posterior corners of head by less than length of basal funicular segment. Antennal scapes with weak longitudinal striae, weakly shining to shining; basal flange well developed, flattened, partly translucent with carinate margin. Psammophore well developed.

Mesosomal profile weakly to moderately convex; all mesosomal surfaces with prominent subparallel, irregular rugae, occasionally rugoreticulate. In dorsal view, humeral shoulders of pronotum enlarged, dorsolateral margins weakly to moderately angulate. Dorsum of promesonotum with longitudinal rugae that diverge anterad toward humeral shoulders of pronotum; promesonotal suture rarely present. Irregular rugae on pronotal sides traverse ventrally or posteroventrally; rugae on mesopleura angle posterodorsally; irregular transverse rugae on propodeal dorsum traverse ventrally or anteroventrally on sides. Superior propodeal spines long, length> 0.6× the distance between their bases, spines connected by well defined keel, tips blunt to acuminate. Inferior propodeal spines slightly wider than high, tip weakly blunt to acuminate, height less than that of superior spines. Propodeal spiracles narrowly ovate facing posterad. Interrugae on mesosoma densely granulate, dull to weakly shining. Legs weakly shining to shining.

Petiolar peduncle about as long as petiolar node, anteroventral margin often with broad, rounded expansion, but lacking triangular process. In profile, posterior surface of petiolar node weakly convex; petiolar node asymmetrical with anterior surface shorter than posterior surface, apex angulate to weakly rounded. In dorsal view, petiolar node longer than wide, widest near rounded anterior margin, narrowing to posterior margin. Sides and posterior face of petiolar node with regular to irregular transverse rugae, occasionally traversing longitudinally or obliquely near anterior margin. Dorsum of postpetiole convex in profile; in dorsal view, widest at or near posterior margin, narrowing to anterior margin, maximum width and length about equal. Transverse rugae on dorsum of postpetiole finer, denser than those on posterior surface of petiolar node; interrugae on both surfaces weakly to moderately granulate-punctate, weakly shining. Striae extend over anterior one-half or more of first gastral tergum; posterolateral margins and other areas lacking striae moderately to strongly coriarious, dull to weakly shining.

Erect, white pilosity moderately abundant on head, often variable in length, longest hairs similar to MOD. Moderately abundant suberect to semidecumbent pilosity on scapes; abundant decumbent hairs on funicular segments. Legs with moderately abundant suberect to decumbent white setae. Mesosoma, petiolar node, postpetiole, gastral terga with erect, moderately dense, white setae that are similar in length; most hairs on anterior half of first gastral tergum <0.16 mm long. Head and gaster ferruginous orange to reddish-orange; mesosoma black, often with a weak to moderate orangish infusion on dorsum of promesonotum ( Figure 69 ).

Queen diagnosis. Queens of this species are diagnosed by the following combination of features: (1) caste-specific morphology of the mesosoma related to wing-bearing and presence of ocelli on head, (2) striae on first gastral tergum usually extend to posterior margin, posterolateral margins with striae or moderately to strongly coriarious, weakly shining, (3) head and gaster ferruginous orange; pronotal sides, anepisternum concolorous blackish to black, (4) interrugae on cephalic dorsum moderately to strongly granulate, dull to weakly shining, (5) queens large (HW = 2.34–2.47 mm; PNW = 1.63–1.70 mm; ML = 2.57–3.00 mm), (6) superior propodeal spines moderately long, length usually> 0.5x the distance between their bases, (7) longest hairs on first gastral sternite approximately 0.2–0.4× MOD, and (8) occurring in San Luis, San Juan, and Mendoza and possibly further south ( Figure 70 ).

Measurements —(n = 4). HL 2.02–2.13; HW 2.34–2.47; MOD 0.46–0.49; OMD 0.47–0.52; SL 1.45–1.56; PNW 1.63–1.70; HFL 1.76–2.08; ML 2.57–3.00; PW 0.65–0.70; PPW 0.90–0.93. Indices: SI 60.49–65.00; CI 112.50–118.81; OI 18.93–20.51; HFI 72.43–86.75.

Description. With caste-specific morphology of the mesosoma related to wing-bearing and presence of ocelli on head. In full face view, head wider than long (CI = 112.50–118.81), broadest just posterior to eyes, posterior margin flat. Longitudinal rugae on cephalic dorsum prominent, wavy; in full-face view, medial rugae not diverging to diverging toward posterior corners of head; posterior corners rugose, interrugae on cephalic dorsum and posterior corners moderately to strongly granulate-punctate, dull to weakly shining. Mandibles with seven teeth, dorsal surface coarsely rugose. Psammophore well developed.

All mesosomal surfaces except pronotal sides with subparallel, regular to wavy rugae, rugae on pronotal sides irregular to weakly rugoreticulate; interrugae weakly to moderately granulate-punctate, weakly shining; superior propodeal spines moderately long, length usually> 0.5× the distance between their bases, spines strongly tapered; inferior propodeal spines well developed, wider than tall, apex subangulate to acuminate, height slightly less than length of superior spines. Petiolar peduncle long, ventral surface with a poorly developed, broadly rounded process. In profile, petiolar node asymmetrical with anterior surface shorter than posterior surface, apex subangulate to angulate. Posterior surface of petiolar node with wavy, transverse rugae. In dorsal view, postpetiole about as wide as long; dorsum with wavy, transverse rugae that are finer, denser than those on posterior surface of petiolar node, interrugae on posterior surface of petiolar node and dorsum of postpetiole moderately coriarious, weakly shining. Striae on first gastral tergum usually extend to posterior margin, posterolateral margins with striae or moderately to strongly coriarious, weakly shinning. Most body surfaces with moderately abundant suberect to erect, short to long, whitish to cream colored setae; longest hairs on first gastral sternite approximately 0.2–0.4× MOD, rarely slightly longer. Head, gaster ferruginous orange; mesoscutum, axilla, mesoscutellum orangish-black to blackish-orange; rest of body blackish to black ( Figure 70 ).

Male diagnosis. Males of this species are diagnosed by the following combination of features: (1) striae extend over anterior one-half or more of first gastral tergum, (2) mesoscutum mostly smooth and shining, and (3) notauli absent ( Figure 71 ). Note that the males are unknown for the closely related P. mapuche .

Measurements —(n = 4). HL 2.02–2.13; HW 2.34–2.47; MOD 0.46–0.49; OMD 0.47–0.52; SL 1.45–1.56; HFL 1.76–2.08; ML 2.57–3.00; PW 0.65–0.70; PPW 0.90–0.93. Indices: SI 60.49–65.00; CI 112.50–118.81; OI 18.93–20.51; HFI 72.43–86.75.

Additional material examined. ARGENTINA: Mendoza: Hwy 144 at 5 km SW San Rafael, 2800’, Dec 4, 2003 ( CASC; MCZC; RAJC) ; Rt 143 at 37.8 km NW San Rafael, 3280’, Jan 21, 2008 ( RAJC) ; Reserva Nancuñan , 1800’, Dec 12, 2003 & Oct 31, 2008 & Feb 13, 2009 ( MCZC; RAJC; RGPC) ; Rt 7 at 5.8 km W Desaguadero, 1530’, Dec 28, 2005 ( MCZC; RAJC) ; Rt 7 at 21.7 km E La Dormida, 1740’, Dec 28, 2005 ( RAJC) ; Rt 7 at 9.8 km E La Dormida, 1720’, Jan 23, 2008 ( RAJC) ; Portrerillos , Nov 21, 2009 ( RGPC) , no date ( USNM); Dec 9–19, 1950 ( IFML) ; Rt 7 at 3.0 km SE Potrerillos, 4710’, Dec 29, 2005 ( RAJC) ; La Pampa de la Carrera, 4760’, Dec 30, 3005 ( RAJC) ; Rt 39 in Valle de Uspallata, 7040’, Dec 31, 2005 ( RAJC) ; Uspallata , Dec 29, 2005 ( RGPC) ; Rt 143 at 4 km SE Pareditas, 3610’, Jan 21, 2008 ( RAJC) ; Rt 143 at 44.8 km SE Pareditas, 4450’, Jan 21, 2008 ( IFML; RAJC) ; Rt 7 at 19.8 km E La Paz, 1520’, Jan 23, 2008 ( RAJC) ; 38.4 km S Jct Rts 7 & 153, 1870’, Jan 23, 2008 ( IFML; RAJC) ; Alto Pencoso, no date (MHNG); 138.1 km S Jct Rts 7 & 153, 1690’, Jan 24, 2008 ( RAJC) ; El Salto , Dec 17, 1950 ( IFML; LACM; MCZC) ; no loc., no date (IFML). San Juan: Rt 12 at 82.0 km NE Calingasta, 6580’, Feb 6, 2010 ( RAJC) . San Luis: Rt 188 at 32.0 km W Union, 1360’, Jan 27, 2008 ( RAJC) ; no loc, no date (MHNG; MLPA) ( Figure 68B ).

Etymology. The specific epithet, propinqua (from Latin, propinquus = near, neighboring, close), is derived from this species having morphology and coloration that is very similar to that of P. carbonarius .

Discussion. Pogonomyrmex propinqua is separated from most congeners by: (1) striae extend over anterior one-half or more of first gastral tergum, posterior margin with striae or moderately to strongly coriarious, and posterolateral margins moderately to strongly coriarious, weakly shining to dull. These characters separate P. propinqua from all but three congeners: P. carbonarius , P. mapuche , and P. weiseri .

Pogonomyrmex propinqua is most closely related to P. weiseri , from which it is separated by: (1) longitudinal rugae on dorsum of promesonotum irregular to rugoreticulate, with short lateral branches that usually contact one another, and (2) interrugae on cephalic dorsum strongly granulate-punctate, dull, with a beaded appearance. In P. weiseri : (1) longitudinal rugae on dorsum of promesonotum more regular, usually do not contact one another and lack short lateral branches, and (2) interrugae on cephalic dorsum weakly to moderately granulate-punctate, weakly shining, with a weakly beaded appearance. These two species are also separated geographically as P. propinqua occurs in more southern provinces (San Luis and Mendoza) than P. weiseri (La Rioja to Salta).

Pogonomyrmex propinqua is separated from P. mapuche based on: (1) ferruginous orange head and gaster and a black mesosoma, (2) long superior propodeal spines, length usually> 0.6x the distance between their bases, and (3) mandibles with six teeth. In P. mapuche : (1) head is dark red to reddish-black, rest of body black, (2) the superior propodeal spines reduced to tubercles or denticles, rarely as short teeth, and (3) mandibles with seven teeth for some to most workers in a series.

Pogonomyrmex propinqua is separated from P. carbonarius by: (1) head and gaster concolorous light to dark ferruginous orange, (2) superior propodeal spines long, length usually> 0.6× the distance between their bases, and (3) most hairs on anterior half of first gastral tergum <0.16 mm long. In P. carbonarius : (1) color variable: concolorous black or with head and gaster reddish-orange to dark blackish-orange to black with a weak orangish infusion, gaster often notably darker than head, (2) at least some workers in a series with superior propodeal spines that consist of tubercles, denticles, or short spines with a length <0.3× the distance between their bases, and (3) several to most hairs on anterior half of first gastral tergum> 0.18 mm long. These two species are easily separated with queens or males when these castes are available (see keys). Pogonomyrmex propinqua and P. carbonarius have mostly non-overlapping distributions, but they co-occur or occur in close proximity in Mendoza Province from Potrerillos south to San Rafael.

Kusnezov (1951) placed the then undescribed P. propinqua under P. rastratus for reasons that were not all his fault (see discussion under P. rastratus ). Most importantly, Kusnezov did not examine syntypes of P. rastratus , but rather indicated that he identified his specimens based on workers from Alto Pencoso (San Luis Province) that A. Forel had identified as P. rastratus (specimens at MHNG); these specimens were actually P. propinqua . To his credit, Kusnezov (1951) indicated that he had several hundred workers from the type locality for P. rastratus (the surroundings of Mendoza) that did not completely correspond to the original description. Kusnezov also discussed the very different descriptions of P. rastratus given in Mayr (1870) and Mayr (1887). He also indicated that P. weiseri var. neuquensis was a synonym of P. rastratus without further discussion, believing that this variety was what is herein named P. propinqua . In synonymizing these two forms, Kusnezov indicated only that P. weiseri was actually a synonym of P. rastratus , and that Santschi used Mayr’s incorrect description of P. rastratus . I have examined syntypes of P. rastratus , P. weiseri , and P. weiseri var. neuquensis (the latter is a junior synonym of P. carbonarius –see above), and it is clear that all three forms comprise distinct species.

Biology. Workers of this species are solitary foragers. Colony size of P. propinqua averages 997 + 114 plus 268 larvae and pupae ( Nobua Behrmann et al., 2010). Reproductive sexuals have been collected in nests from December 28–February 4. Founding queens forage in the field (R. Pol, pers. comm.), but it is not known if they are obligate or facultative foragers (see Johnson, 2006). Mating flights occur during the austral summer, and they appear to be triggered by rain (R. Pol, pers. comm., R.A. Johnson, pers. obs.).

As noted in above the taxonomic history, several papers have studied P. propinqua ( Claver & Fowler, 1993; Nobua-Behrmann et al., 2013; Nobua Behrmann et al., 2010; Pirk & Lopez de Casenave, 2006, 2010, 2011; Pirk et al., 2007; Pirk et al., 2004; Pirk et al., 2009; Pol & Lopez de Casenave, 2004; Pol et al., 2011), but all of these papers misidentified the species as P. rastratus , and all papers should be referred to P. propinqua .

Pogonomyrmex propinqua appears to be restricted to Mendoza, San Luis, and San Juan Provinces at elevations from 30–2135 m, but its distribution may extend further south and east in the Lower Monte Desert. This species occurs in the Lower Monte and Dry Chaco ecoregions, as defined by Olson et al. (2001) ( Figure 68B ).

Figures

FIGURE 68. Geographic distribution of: (A) Pogonomyrmex pronotalis, (B) P. propinqua, (C) P. pulchellus. The large black circle in each panel denotes the type locality. See text regarding the type locality for P. pulchellus.

FIGURE 69. Photographs of Pogonomyrmex propinqua holotype worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922160). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 70. Photographs of Pogonomyrmex propinqua alate queen: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922465). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 71. Photographs of Pogonomyrmex propinqua male: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922460). Photographs by Michele Esposito from www.AntWeb.org.