Pogonomyrmex abdominalis

A widely distributed but apparently relatively uncommon South American species.

Identification
Johnson (2015) - Worker Within the P. naegelii-group, the combination of: (1) approximately 8–10 coarse, longitudinal rugae between frontal lobes, (2) lacking small lobe that projects dorsally from anterior margin of antennal fossa, (3) peduncle of petiole and anterior surface of petiolar node meet at or near a right angle, (4) in dorsal view, posterior surface of petiolar node distinctly wider than distance between tips of superior propodeal spines, and (5) longest hairs on mesosoma approaching to slightly >MOD uniquely characterize this species.

Queen This caste is diagnosed by: (1) caste-specific morphology of the mesosoma related to wing-bearing and presence of ocelli on head, (2) small (HW < 1.35 mm), (3) petiolar node and postpetiole wide (petiolar node > 0.50 mm, postpetiole > 0.70 mm), (4) posterior surface of petiolar node granulate-punctate, and (5) longitudinal rugae on mesoscutum and mesoscutellum.

Pogonomyrmex abdominalis co-occurs with the other two P. naegelii-group species. Pogonomyrmex abdominalis can be distinguished from Pogonomyrmex tenuipubens based on the following characters: (1) hairs on the mesosoma and psammophore are coarse and much longer than width of cephalic interrugae, and (2) approximately 8–10 coarse rugae between frontal lobes. In P. tenuipubens: (1) the abundant hairs on the mesosoma and psammophore are thin and delicate, their maximal length is similar to the width of cephalic interrugae, and (2) more than 15 fine rugae are present between the frontal lobes. Pogonomyrmex abdominalis is distinguished from Pogonomyrmex naegelii based on the following characters: (1) usually larger (HW = 1.14–1.33 mm), (2) lacking small lobe that projects dorsally from anterior margin of antennal fossa, (3) peduncle of petiole and anterior surface of petiolar node meet at or near a right angle, and (4) the posterior surface of petiolar node wider than distance between tips of superior propodeal spines. In P. naegelii: (1) the body is usually smaller (HW = 1.05–1.23 mm), (2) a small lobe projects dorsally from the anterior margin of the antennal fossa, (3) the peduncle of petiole and anterior surface of petiolar node meet at an obtuse angle, and (4) the width of the posterior surface of petiolar node is similar to or slightly greater than the distance between the tips of the superior propodeal spines.

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

Biology
Johnson (2015) - Pogonomyrmex abdominalis is a solitary forager. Nests usually have a tumulus that is up to 15 cm in diameter. All series collected by the author were in open, grassy, park-like habitats. Colonies probably contain up to about 500 workers.

Pogonomyrmex abdominalis appears to be a relatively uncommon species that has a wide geographic distribution. Little is known about the biology of P. abdominalis but it is probably similar to that of P. naegelii. Alate queens were collected as part of the type series (no date) and on 24 February, suggesting that mating flights occur during the austral summer. Additional queens need to be collected to determine if P. abdominalis also produces ergatoid queens, as occurs in P. naegelii and related North American species (Heinze, Hölldobler, & Cover, 1992; Johnson et al., 2007).

Pogonomyrmex abdominalis appears to be a lowland species that inhabits sites at elevations from 10–1000 m. This species occurs in the Dry Chaco, Humid Pampas, Uruguayan Savanna, Alto Paraná Atlantic Forest, Cerrado, Bahia Interior Forests, and Beni Savanna ecoregions as defined by Olson et al. (2001). It is likely that P. abdominalis occurs in several additional ecoregions given the few records that are scattered over a very large geographic area.

Castes
Males have yet to be collected.

Nomenclature

 *  abdominalis. Pogonomyrmex (Ephebomyrmex) naegeli st. abdominalis Santschi, 1929d: 278 (w.q.) BRAZIL. Combination in Ephebomyrmex: Kempf, 1972a: 106; in Pogonomyrmex: Bolton, 1995b: 339. Raised to species: Kusnezov, 1951a: 250.

Worker
Johnson (2015) - Lectotype (n = 31). HL 1.25 (1.17–1.41); HW 1.26 (1.14–1.33); MOD 0.26 (0.25–0.30); OMD 0.28 (0.24–0.33); SL 0.84 (0.87–0.99); PNW 0.82 (0.75–0.92); HFL 1.09 (1.03–1.27); ML 1.38 (1.33–1.55); PW 0.38 (0.34–0.43); PPW 0.49 (0.46–0.54). Indices: SI 66.67 (70.08–85.09); CI 100.80 (92.37–105.69); OI 20.63 (20.49–24.56); HFI 86.51 (83.46–103.31).

Head subquadrate to quadrate (CI = 92.37–105.69), widest just posterior to eye; posterior margin flat to weakly concave. Longitudinal rugae on cephalic dorsum prominent, occasionally weakly rugoreticulate especially near posterior margin; approximately 8–10 coarse, longitudinal rugae between frontal lobes; in full-face view, medial rugae not diverging toward posterior corners of head. In profile, area posterior to eyes rugose to moderately rugoreticulate, rugae not converging toward vertex. Cephalic interrugae moderately to strongly granulate, dull to weakly shining; vertex rugose. Anterior margin of clypeus moderately to strongly concave, dorsal surface with numerous subparallel, longitudinal rugae; lacking small lobe that projects dorsally from anterior margin of antennal fossa. Mandible with six teeth; mandibular dorsum coarsely rugose. Up to several moderately long, curved, bristle-like, yellow-brown to brownish hairs project from anterior margin of clypeus and basolateral margin of mandibles. MOD ranging from 0.20–0.25x HL. In profile, eyes situated anterior to middle of head, OMD = 0.80–1.19x MOD. Antennal scapes moderately long (SI = 66.67–85.09), failing to reach vertex by 1.0–1.5x length of basal funicular segment; entire scape with strong longitudinal striae, dull to weakly shining; basal flange of scape flattened and well-developed with carinate margin. Psammophore poorly-developed, consisting of short to medium-length hairs scattered across ventral side of head.

Mesosomal profile convex; all mesosomal surfaces with highly irregular rugae, rugoreticulate, or vermiculate. Mesoepinotal sulcus not impressed. Dorsum of promesonotum and sides of pronotum rugoreticulate to vermiculate. Mesopleura with irregular rugae angling posterodorsally to rugoreticulate. Dorsum of propodeum with wavy to irregular transverse rugae that traverse anteroventrally, becoming more irregular on sides. Superior propodeal spines moderately long, acuminate, connected by well-defined keel; spine length approximately 0.7–0.8x distance between their bases. Inferior propodeal spines well-developed, acuminate, length approximately 0.5–1.0x that of superior spines, base wider than length of superior spines; inferior and superior spines connected by weak crest. Propodeal spiracles ovoid to circular facing posterad. Interrugae on mesosoma moderately granulate, weakly shining to smooth and strongly shining. Legs moderately coriarious, weakly shining.

Peduncle of petiole about as long as petiolar node, anteroventral margin with a weakly to strongly-developed triangular process. In profile, petiolar node asymmetrical with anterior surface shorter than posterior surface; apex weakly rounded to subangulate; anterior surface meeting peduncle at or near a right angle. In dorsal view, petiolar node longer than wide, widest near middle, narrowing to spatulate to rounded anterior margin; aximal width of posterior surface greater than distance between tips of superior propodeal spines; dorsum and sides strongly rugoreticulate to vermiculate, interrugae granulate, dull to weakly shining. Dorsum of postpetiole convex in profile; in dorsal view, postpetiole robust, widest at or near posterior margin, narrowing from near middle to weakly truncate anterior margin; maximal width slightly greater than length; dorsum and sides weakly to moderately rugoreticulate or with several irregular longitudinal to oblique rugae, interrugae moderately to strongly granulate, dull to weakly shining. Ventral process of postpetiole large, bulbous, height similar to dorsal portion of postpetiole. First gastral tergum weakly to strongly coriarious, dull to weakly shining to smooth and strongly shining; anterior margin sometimes with weak longitudinal striae.

Erect yellow-brown to brownish pilosity moderately abundant on head, variable in length, mostly short to medium-length, often with one or more longer hairs that approximate MOD. Moderately abundant suberect to semidecumbent pilosity on scape, abundant decumbent hairs on funicular segments. Legs with moderately abundant semidecumbent brownish setae. Mesosoma, petiolar node, postpetiole, gastral terga with moderately dense, erect setae, mostly similar in length, longest approaching to slightly >MOD; hairs on propodeum less dense. Concolorous tan to tannish-brown with darker gaster.

Queen
Johnson (2015) - (n = 4). HL 1.19–1.35; HW 1.24–1.30; MOD 0.30–0.32; OMD 0.27–0.31; SL 0.69–0.75; PNW 1.00–1.03; HFL 0.92–0.95; ML 1.56–1.65; PW0.54–0.57; PPW 0.71–0.76. Indices: SI 54.33–57.69; CI 95.38–106.72; OI 23.08–25.20; HFI 72.44–76.61.

Type Material
Johnson (2015) - Syntypes examined: 8 workers, 4 queens, ARGENTINA, Córdoba: Sierras de Córdoba, Alta Gracia La Granja, #1710 (Charles Bruch leg.). See also Gallardo, 1932: 112. MACN worker here designated LECTOTYPE [CASENT0235285].

In his description, Santschi listed Alta Gracia, Córdoba, as the type locality for P. abdominalis, as did all subsequent authors (see Gallardo, 1932; Kempf, 1972; Kusnezov, 1951). However, labels on all syntypes say, “Alta Gracia La Granja, Sierras de Córdoba”. Alta Gracia and La Granja are two small towns that are located approximately 75 km apart along the eastern side of the Sierras de Córdoba. Thus, the labels suggest that the type locality was somewhere between these two towns.

Etymology
Johnson (2015) - The specific epithet, abdominalis (from Latin, abdomen- = abdomen), appears to be derived from the enlarged postpetiole on this species, which Santschi described as wider than long for the worker and even larger and more pronounced in the queen.