Pogonomyrmex uruguayensis

Robert A. Johnson, 2015, A taxonomic revision of South American species of the seed-harvester ant genus Pogonomyrmex (Hymenoptera: Formicidae). Part I, Zootaxa 4029 (1), pp. 1-142 : 74-79

Pogonomyrmex uruguayensis

( Figures 28, 35–37)

Pogonomyrmex uruguayensis Mayr, 1887: 614 (worker). Syntypes examined: 1 worker [MSNG], 1 worker [NMW], URUGUAY, no location (Prof. C. Berg). See also Gallardo, 1932: 148, fig. 32. NMW worker here designated LECTOTYPE [CASENT0173373].

Pogonomyrmex uruguensis Mayr : Santschi, 1921: 95.

Worker. Diagnosis. Within the P. bispinosus -group, the combination of: (1) superior propodeal spines welldeveloped, (2) smaller (HW = 1.24-1.61 mm), (3) in frontal view and from posterior margins of head looking down over cephalic dorsum, frontal lobes poorly-developed, lateral margins subparallel, projecting nearly parallel to cephalic dorsum uniquely characterize this species ( Figures 28 & 35).

Measurements —lectotype (n = 21). HL 1.55 (1.28–1.62); HW 1.54 (1.24–1.61); MOD 0.33 (0.30–0.40); OMD 0.37 (0.30–0.41); SL 1.04 (0.86–1.14); PNW 1.06 (0.88–1.15); HFL 1.31 (1.19–1.57); ML 1.67 (1.51–2.05); PW 0.41 (0.33–0.50); PPW 0.55 (0.47–0.63). Indices: SI 67.53 (64.56–77.42); CI 99.35 (93.23–105.41); OI 21.43 (21.15–26.28); HFI 85.06 (84.46–100.73).

Redescription. Head subquadrate to quadrate (CI = 93.23–105.41), widest just posterior to eyes; posterior margin flat in full-face view. Longitudinal rugae on cephalic dorsum weak, wavy to irregular; in full-face view, medial rugae diverging weakly towards posterior corners of head. In profile, rugae posterior to eyes converging near vertex, occasionally weak to indistinct near vertex. Cephalic interrugae strongly granulate, dull; vertex moderately granulate or rugose, interrugae weakly to moderately granulate, weakly shining to shining. In frontal view and from posterior margins of head looking down over cephalic dorsum, frontal lobes poorly-developed, lateral margins subparallel, projecting nearly parallel to cephalic dorsum. Anterior margin of clypeus concave; dorsal surface with several subparallel longitudinal rugae. Mandible with six teeth; mandibular dorsum coarsely rugose. MOD ranging from 0.21–0.28x HL. In profile, eyes situated slightly anterior to middle of head, OMD = 0.88–1.25x MOD. Antennal scapes moderately long (SI = 64.56–77.42), failing to reach vertex by length of basal funicular segment; entire scape with longitudinal striae. Psammophore well-developed.

Mesosomal profile strongly convex; all mesosomal surfaces with prominent irregular rugae to rugoreticulate. Anterior margin of pronotal dorsum with irregular transverse rugae or moderately rugoreticulate, humeral shoulders on pronotum and pronotal sides rugoreticulate or with rugae that traverse posteroventrally or longitudinally; dorsum of mesonotum with irregular, longitudinal rugae that diverge anteriorly to rugoreticulate or vermiculate; rugae on mesopleura longitudinal or traversing posterodorsally; dorsum of propodeum with irregular transverse to oblique rugae or rugae lacking; rugae traverse ventrally or anteroventrally on propodeal sides. Interrugae on pronotum and mesonotum moderately to strongly granulate, dull to weakly shining, those on propodeum very strongly granulate, very dull to dull. Superior propodeal spines moderately long, slightly shorter than width between their bases. Inferior propodeal spines lacking. Propodeal spiracles narrowly ovate facing posterad. Legs moderately to strongly coriarious, weakly shining.

Penduncle of petiole about 0.7x as long as petiolar node, anteroventral margin with poorly-developed, broadly rounded process. In profile, petiolar node asymmetrical with anterior surface shorter than posterior surface; apex broadly rounded. In dorsal view, petiolar node longer than wide, widest near spatulate anterior margin. Sides and dorsum of petiolar node with weak, wavy to irregular, transverse rugae; interrugae moderately to strongly granulate-punctate, dull to weakly shining. Dorsum of postpetiole convex in profile; in dorsal view, widest at or near posterior margin and tapering to anterior margin, maximal width about equal to length, weakly to strongly coriarious, dull to weakly shining; sides of postpetiole often with weak transverse rugae. First gastral tergum moderately to strongly coriarious, weakly shining.

Erect whitish to yellowish pilosity moderately abundant on head, variable in length, longest hairs not exceeding MOD. Moderately abundant suberect to semidecumbent pilosity on scape; abundant decumbent hairs on funicular segments. Legs with moderately abundant suberect to decumbent white setae. Mesosoma, petiolar node, postpetiole, first gastral tergum with moderately dense erect white setae, often similar in length, longest hairs much shorter than MOD. Body concolorous tannish-brown to reddish-brown, head sometimes slightly lighter than rest of body ( Figures 28 & 35).

Queen. Diagnosis. This caste is diagnosed by: (1) caste-specific morphology of the mesosoma related to wingbearing and presence of ocelli on the head, (2) superior propodeal spines present, (3) inferior propodeal spines absent, (4) rugae on cephalic dorsum wavy to irregular, interrugae distinctly wider than rugae, (5) posterior surface of petiolar node and usually dorsum of postpetiole rugose (usually transverse), rugae on dorsum of postpetiole often faint to absent medially, (6) in profile, apex of petiolar node subangulate to angulate, and (7) body concolorous tannish-brown ( Figure 36).

Measurements —(n = 12). HL 1.64–1.76; HW 1.72–1.83; MOD 0.36–0.47; OMD 0.38–0.45; SL 1.08–1.18; PNW 1.27–1.48; HF 1.40–1.63; ML 2.24–2.50; PW 0.50–0.63; PPW 0.70–0.81. Indices: SI 60.34–68.60; CI 100.00–105.29; OI 20.93–27.33; HFI 81.40–93.02.

Description. With caste-specific morphology of the mesosoma related to wing-bearing and presence of ocelli on head. In full-face view, head quadrate to slightly wider than long (CI = 100.00–105.29), widest just posterior to eyes, posterior margin flat. Longitudinal rugae on cephalic dorsum prominent, wavy to irregular; in full-face view, medial rugae not diverging toward posterior corners of head, interrugae weakly granulate-punctate, weakly shining to shining; vertex rugose, interrugae weakly granulate-punctate, weakly shining to shining. Mandible with six teeth, dorsal surface coarsely rugose. Psammophore well-developed.

All mesosomal surfaces with subparallel, regular, wavy, or irregular rugae; interrugae on mesoscutum and mesoscutellum weakly coriarious, weakly shining to shining, those on propodeum moderately to strongly granulate-punctate, dull; propodeum with short superior spines; inferior propodeal spines absent. Peduncle of petiole long, anteroventral margin with weakly to moderately well-developed triangular process. In profile, petiolar node asymmetrical with anterior surface notably shorter than posterior surface, apex rounded to weakly angulate. Posterior surface of petiolar node and dorsum of postpetiole with irregular transverse rugae; rugae on postpetiole weaker, often faint to absent medially; interrugae on posterior surface of petiolar node and dorsum of postpetiole weakly granulate-punctate, weakly shining. First gastral tergum weakly coriarious, shining to strongly shining. Most body surfaces with moderately abundant suberect to erect, medium-length, white to yellowish setae; moderately abundant suberect to erect hairs on first gastral tergum, those on second and third terga restricted to posterior margin. Body mostly concolorous tannish-brown ( Figure 36).

Male. Diagnosis. This caste is diagnosed by: (1) first gastral tergum lacking striae, (2) in full-face view, external margin of apical tooth curved inward, (3) dorsum of postpetiole strongly granulate, dull, to occasionally very weakly rugoreticulate to vermiculate, interrugae dull, (4) rugae on head usually rugoreticulate to vermiculate, (5) pronotal sides and mesopleura with occasional rugae, (6) interrugae on cephalic dorsum, pronotal sides, and mesopleura moderately to strongly granulate, dull, and (7) notauli present ( Figure 37).

Measurements —(n = 3). HL 1.32–1.42; HW 1.38–1.51; MOD 0.50–0.54; OMD 0.26–0.29; SL 0.37–0.40; HFL 1.56–1.68; ML 2.60–2.68; PW 0.52–0.57; PPW 0.68–0.72. Indices: SI 24.50–27.54; CI 104.55–109.49; OI 34.67–36.23; HFI 103.31–121.01.

Additional material examined. ARGENTINA: Catamarca: Rt 20 at 0.7 km NE Esquiú, 800’, Mar 21, 2015 (RAJC); Rt 157 at 25.2 km NNW Jct Rt 60, 750’, Mar 21, 2015 (RAJC). Chaco: Rt 11 at 26.6 km S Resistencia, 170’, Jan 19, 2011 (RAJC); 42 km SW Resistencia, Dec 18, 2005 (CSC). Córdoba: Rt 2 at 18.9 mi E Villa María, 470’, Dec 21, 2005 (CASC; CSC; RAJC); Rt 65 at 22.4 km E Villa María, Dec 18, 2005 (CSC); Rt 9 at 6.5 mi E Bell Ville, 390’, Dec 21, 2005 (CSC; RAJC); Rt 16 at 15.2 km N Chuña, 1670’, Mar 20, 2015 (RAJC); Rt 60 at 4.2 km SE Quilino, 1520’, Mar 20, 2015 (RAJC); Rt 60 at 27.7 km NW Quilino, 700’, Mar 21, 2015 (RAJC); Rt 60 at 12.3 km NW Lucio Mansilla, 680’, Mar 21, 2015 (RAJC). Corrientes: Rt 12 at 10.2 km E Santa Ana, 210’, Jan 18, 2011 (RAJC); no loc, no date (USNM). Entre Ríos: Parque Nacional El Palmar, Jan 6, 2006 (RGPC); Rt 130 at 2.7 mi S Villaguay, 190’, Dec 19, 2005 (CSC; RAJC); Villaguay, no date (MACN; MLPA); no loc, no date (MACN). Formosa: Reserva "El Bagual", 151 m, Apr 2009 (RAJC); Guaycolec, no date (MACN; NHMB); Estancia Sosa, no date (MACN). La Rioja: Rt 79 at 30.1 km N Catuna, 1890’, Mar 19, 2015 (RAJC); Rt 79 at 14.2 km S Catuna, 1810’, Mar 19, 2015 (RAJC); Rt 79 at 34.6 km S Catuna, 2050’, Jan 22, 2006 (MCZ; RAJC); Rt 79 at 2.6 km N Ulapes, Mar 19, 2015 (RAJC); Rt 79 at 6.9 km SE Ulapes, 1250’, Jan 22, 2006 (RAJC); Rt 79 at 26.8 km SE Ulapes, 960’, Mar 19, 2015 (RAJC); Rt 79 at 4.2 km S Jct Rt 141, 1750’, Mar 19, 2015 (RAJC); Rt 38 at 8.1 km W of Córdoba-La Rioja border, 710’, Jan 14, 2010 (RAJC); Rt 38 at 2.3 km W Córdoba border, Mar 20, 2015 (RAJC); Rt 38 at 42.1 km ESE Chamical, Mar 20, 2015 (RAJC); Rt 60 at 15.4 km NE Jct Rt 20, 660’, Mar 23, 2015 (RAJC). Salta: Estacion Ferrocarril Virgilio Tedin, Feb 28, 1948 (FML). San Luis: Rt 7 at Alto Pencoso, 2150’, Dec 20, 2006 (RAJC); La Tranca, Feb 10 & 24, 2009 (RGPC); La Punta, 2790’, Mar 6, 2005 (RAJC); Rt 20 at 1 km NE Luján, 1940’, Dec 26, 2005 (RAJC); Rt 7 at 3.5 km W Alto Pencoso, Dec 20, 2006 (CSC). Santa Fe: Paraná River floodplain at Villa Ocampo, 45 m, Nov 21, 2004 (RAJC); Ocampo, 50 m, Nov 17, 2003 (CASC; RAJC); Rt 11 at 23 mi S Villa Ocampo, 140 m, Dec 20, 2004 (RAJC); Rt 34 at 3 km W Santa Ana, 145 m, Dec 20, 2006 (RAJC); 22 km S Reconquista, 45 m, Nov 15, 2003 (RAJC); Villa Guillermina, no date (LACM); Rosario, no date (MACN); Fives Lille, no date (MACN); 18.2 km S Los Toscas, Dec 4, 2005 (CSC). Santiago del Estero: Rt 34 at 33.6 km N Pozo Hondo, 820’, Apr 7, 2015 (RAJC). Tucumán: Rt 34 at 70.8 km SE Jct Rt 9, 1400’, Apr 7, 2015 (RAJC). PARAGUAY: Boquerón: Rt Trans-Chaco, 180 m, Dec 4, 2002 (ALWC). Ñeembucú: Pila Aeropuerto, 65 m, Dec 12, 2002 (ALWC). Presidente Hayes: Rt Trans-Chaco at km 438, Dec 5, 1993 (ALWC); Rt Trans-Chaco at km 140, Dec 3, 1993 (ALWC); Rt Trans-Chaco, 90 m, Dec 3, 2002 (ALWC); Monte Lindo, Nov 15, 1993 (ALWC). URUGUAY: Paysandú: Arroyo Sacra, Feb 25, 1961 (LACM). Locations not found: URUGUAY: Rivera: Río Negro, Feb 1941 (FML). Dpto. Unknown : no loc, no date (MCZ; NMW) ( Figure 31 C).

Etymology. The specific epithet, uruguayensis was derived from Charles Berg collecting the series of syntype workers in Uruguay (the exact location was unspecified).

Discussion. Pogonomyrmex uruguayensis co-occurs with P. inermis . The two species are easily distinguished as P. uruguayensis has superior propodeal spines while these spines are lacking or reduced to small denticles or tubercles in P. inermis . Additionally, workers of P. uruguayensis are typically smaller (HW = 1.24–1.61 mm) than those of P inermis (HW = 1.59–1.86 mm). Pogonomyrmex uruguayensis is distinguished from other sympatric congeners by its well-developed psammophore and absence of transverse rugae on the dorsum of the postpetiole.

I also examined five workers that Santschi had labelled as “syntypes” of P. uruguayensis var. spinosula from Guaycubec (=Guaycolec?), Formosa, Argentina (NHMB). Santschi (1921) described this variety, but did not name it as a new variety, such that these specimens are not true syntypes and the name is unavailable.

Gallardo (1932, pg. 131) mentioned that Santschi had identified one worker of P. bispinosus from Formosa, Argentina, that coincided well with the description, but that it was far from all Chilean records. I did not examine this specimen, but it was undoubtedly P. uruguayensis .

Biology. Pogonomyrmex uruguayensis is a solitary forager that harvests the seeds of various grass and nongrass species, but very loose columns of scattered foragers also have been observed. Nests are cryptic or they can have a tumulus up to 10 cm in diameter; nests occasionally have a small (5–10 cm in diameter) external midden of seed chaff. Most colonies of P. uruguayensis appear to be small and probably contain about 300–500 workers, but sometimes reach up to approximately 1000 workers.

Collection dates for sexuals range from 30 November to 21 December. Mating flights have not been observed, but they occur during the austral summer (December–January) based on finding dealate queens on the ground on 19 & 26 December. Several dealate queens also were collected foraging outside the nest. Several ant species have queens that sometimes apparently forego mating and later perform tasks such as foraging and nest maintenance (Peeters, 1997). Reproductive status was not determined for these queens, but they are assumed to have been unmated given that foraging queens (both ergatoid and dealate) are unmated in P. pi ma, which is the only species in which such queens have been dissected (Johnson et al., 2007). These observations add another Pogonomymex to the list of species in which queens forage outside the nest (Johnson et al., 2007).

Pogonomyrmex uruguayensis inhabits sites at elevations from 50–845 m. This species occurs in the Dry Chaco, Humid Chaco, Uruguayan Savanna, northern Espinal, and northern Humid Pampas ecoregions as defined by Olson et al. (2001) ( Figure 31 C).