Pogonomyrmex excelsior, 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 : 79-82

Pogonomyrmex excelsior NEW SPECIES

( Figure 35 )

Distribution—36A

Holotype worker [ MACN: CASENT0922462 ]: ARGENTINA, Jujuy: Departamento Susques, Jct Rutas 52 & 16 (16.7 km W Susques), 23º24.0’S 66º31.2’W, 13,470 (4080 m), 1 April 2015 (R.A. Johnson #5417) . Paratypes, same data as holotype: IFML (6w) , MACN (12w) , LACM (6w), MCZC (6w), RAJC (24w), UCDC (3w), USNM (3w). Additional paratype series from the same locality and date–RAJ #5418: MACN (3w) , RAJC (6w) ; RAJ #5419: IFML (3w), MACN (3w) , MCZC (3w), RAJC (9w), USNM (3w).

Worker diagnosis. Workers of this species are uniquely characterized by the following combination of features: (1) striae extend over anterior two-thirds or more of medial portion of first gastral tergum, posterolateral margins usually smooth and shining, (2) head dark reddish-black to blackish-red; malar area, gaster blackish to black; mesosoma and gaster dark blackish-red to black; in dorsal view, pronotum darker than mesonotum for some to all workers in a series, and (3) restricted to high elevation and altiplano habitats (> 3000 m) of northwestern Argentina, northeastern Chile, and probably Bolivia ( Figure 35 ).

Measurements — holotype (n = 6 + 6 paratypes). HL 1.62 (1.44–1.76); HW 1.64 (1.49–1.75); MOD 0.36 (0.34– 0.39); OMD 0.40 (0.33–0.46); SL 1.29 (1.01–1.36); PNW 1.12 (1.02–1.21); HFL 1.80 (1.56–1.82); ML 1.80 (1.67– 2.05); PW 0.42 (0.35–0.48); PPW 0.59 (0.53–0.65). Indices: SI 78.66 (66.89–81.17); CI 101.23 (97.16–105.42); OI 21.95 (20.57–24.20); HFI 109.76 (97.01–106.37).

Description. Head subquadrate to quadrate (CI = 97.16–105.42); posterior margin flat to weakly convex in full-face view. Longitudinal rugae on cephalic dorsum prominent, in full-face view, medial rugae diverging toward posterior corners of head; interrugae strongly granulate, with a beaded appearance, dull to weakly shining; posterior corners rugose, interrugae smooth and shining to weakly coriarious, weakly shining. Anterior margin of clypeus moderately concave, medial portion of clypeus with numerous subparallel, longitudinal rugae, occasionally rugae converge anterad to form up to several concentric narrowly rounded Vs. Numerous long, curved, bristle-like, yellowish macrochaetae project from anterior margin of clypeus and ventral side of mandibles. Mandibles with six or occasionally seven teeth; mandibular dorsum coarsely rugose. MOD ranging from 0.21–0.25× HL. In profile, eyes situated slightly anterior to middle of head, OMD = 0.97–1.25× MOD. In full-face view, eyes protruding slightly beyond lateral margins of head. Antennal scapes (SI = 66.89–81.17) failing to reach posterior corners of head by width of basal funicular segment to reaching posterior corners.Antennal scapes moderately striate, striae weakening distally, interstriae weakly coriarious, weakly shining to smooth and shining; basal flange moderately well developed with carinate margin. Psammophore well developed.

Mesosomal profile weakly to moderately convex; all mesosomal surfaces with prominent, regular to irregular, subparallel-parallel rugae or sometimes rugoreticulate. In dorsal view, humeral shoulders of pronotum enlarged, strongly angulate. Promesonotal suture usually present. Regular to irregular longitudinal rugae on mesonotum usually with numerous short, lateral branches to weakly rugoreticulate. Rugae on mesonotum continue to anterior margin of pronotum or anterior margin with one to few transverse rugae; rugae on pronotum regular to irregular with numerous branches; rugae on pronotal sides irregular, usually with numerous secondary rugae to rugoreticulate; rugae usually weaker on pronotal sides (especially posterad) than on mesopleura. Wavy to irregular rugae on mesopleura angle posterodorsally; transverse or oblique rugae on dorsum of propodeum traverse ventrally or anteroventrally on sides. Superior propodeal spines consist of acuminate denticles, teeth, or spines, longest about 0.4× the distance between their bases; spines usually connected by well defined keel. Inferior propodeal spines triangular, wider than high, apex weakly rounded to acuminate, often taller than superior spines. Propodeal spiracles narrowly ovate facing posterad. Interrugae on mesosoma strongly granulate, dull, pronotal sides and mesopleura especially granulate. Legs weakly to moderately coriarious, weakly shining.

Peduncle of petiole about 0.8× the length of petiolar node, anteroventral margin with poorly developed rounded process to a broadly-rounded tongue-shaped process. In profile, posterior surface of petiolar node weakly convex; petiolar node asymmetrical with anterior surface shorter than posterior surface, apex weakly rounded to subangulate. In dorsal view, petiolar node longer than wide, widest near narrowly-rounded to spatulate anterior margin. Posterior surface of petiolar node with irregular, transverse, oblique, longitudinal rugae, or in a combination of directions. Dorsum of postpetiole convex in profile; in dorsal view, widest near posterior margin, narrowing to anterior margin, width and length similar; posterad rugae transverse, anterad rugae transverse or traversing from lateral margin then curving anterad to become longitudinal; anterolateral rugae concentric, curving from lateral to anterior margin. Rugae on dorsum of postpetiole finer, denser than those on posterior surface of petiolar node, interrugae weakly to moderately coriarious, weakly shining. Striae cover anterior two-thirds or more of medial portion of first gastral tergum, posterior margin smooth and shining, occasionally moderately coriarious, weakly shining; posterolateral margins smooth and shining.

Erect, short to medium length, whitish pilosity moderately abundant on head, most hairs <0.2–0.3× MOD. Moderately abundant semidecumbent to decumbent pilosity on scape; abundant decumbent hairs on funicular segments. Legs with moderately abundant suberect to decumbent whitish setae. Rest of body with moderately dense, erect, medium length, whitish setae; hairs on mesosoma usually about 0.5–0.6× MOD; hairs on first gastral tergum shorter, more delicate than those on mesosoma. Head dark reddish-black to blackish-red, usually with part of cephalic dorsum posterior to frontal lobes blackish to black; malar area, gaster blackish to black; mesosoma dark blackish-red to black; in dorsal view, pronotum darker than mesonotum for some to all workers in a series ( Figure 35 ).

Queen. Unknown.

Male. Unknown.

Additional material examined. ARGENTINA: Jujuy: Rt 40 at 41.5 km N Coranzuli, 13,390’, Apr 3, 2015 ( RAJC) ; Rt 52 at 28.6 km SW Susques, 13,040, Apr 1, 2015 ( RAJC) . CHILE: Antofagasta: Rt 27 at 3.5 km E Argentina border, 14,080’, Apr 2, 2017 ( RAJC) ; Rt 27 at 0.1 km E Argentina border, 14,090’ Apr 2, 2017 ( RAJC) ( Figure 36A ).

Etymology. The specific epithet, excelsior , (from Latin, excelsus, for lofty, elevated, or high plus – ior, suffix forming adjectives’ comparative degree) for this species occurring in high elevation altiplano habitats.

Discussion. Pogonomyrmex excelsior may co-occur with several P. rastratus -group species. However, P. excelsior is distinguished from all congeners by: (1) distinctly dark coloration–dark reddish-black to blackish red head, malar area and gaster blackish to black; mesosoma and gaster dark blackish-red to black; in dorsal view, pronotum darker than mesonotum for some to all workers in a series, but concolorous in some workers, and (2) striae extend over more than anterior two-thirds of medial portion of first gastral tergum.

Biology. Pogonomyrmex excelsior workers are solitary foragers that can travel up to 30–40 m from the nest. Nests of P. excelsior are placed in open, exposed sites, and the entrance ranges from a hole in the ground and lacking a tumulus to a tumulus up to 15 cm in diameter. Nests are most easily located by baiting workers with cookie crumbs, then following them back to the nest. Partial nest excavations indicated that colonies contain approximately 500–1000 workers.

Pogonomyrmex excelsior occurs at elevations from 3950–4080 m. This species inhabits that Central Andean puna and Central Andean dry puna ecoregions, as defined by Olson et al. (2001) ( Figure 36A ).

Figures

FIGURE 35. Photographs of Pogonomyrmex excelsior holotype worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922462). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 36. Geographic distribution of: (A) Pogonomyrmex excelsior, (B) P. forelii, and (C) P. granulatus. The large black circle in each panel denotes the type locality.