Pogonomyrmex varicolor, 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 : 201-209

Pogonomyrmex varicolor NEW SPECIES

( Figures 101–105 )

Distribution—100B

Holotype worker [ MACN: CASENT0922468 ]: ARGENTINA, Chubut: Departamento Escalante, Jct Rts 37 & 26, 45º46.8’S, 68º03.8’W, 2380’ (720 m), 19 February 2014 (R.A. Johnson #5195) . Paratypes, same data as holotype: IFML (3 workers) , LACM (3 workers, MACN (9 workers) , MCZC (12 workers) , RAJC (29 workers, 6 alate queens, 9 males). Additional paratype series from the same locality and date—RAJ #5196: IFML (6 workers) , LACM (9 workers) , MACN (3 workers) , RAJC (6 workers) , UCDC (3 workers), USNM (6 workers) ; RAJ #5197: RAJC (7 workers) .

Worker diagnosis. Workers of this species are uniquely characterized by the following combination of features: (1) striae on first gastral tergum extend over one-half or more of segment, posterolateral margins smooth and shining to weakly coriarious, weakly shining, (2) all striae on first gastral tergum longitudinal, (3) restricted to the Patagonia region of Argentina, (4) workers in a series often with head and mesosoma black, or with head and gaster ferruginous orange to blackish-orange, (5) superior propodeal spines consist of tubercles, denticles, or short teeth, sometimes moderately long to long spines, length <0.5× the distance between their bases for some to all workers in a series, (6) rugae on promesonotum regular to wavy, longitudinal rugae on mesonotum continue to anterodorsal margin of pronotum or diverge to humeral shoulders of pronotum with one to few transverse rugae along anterodorsal margin, and (7) interrugae on promesonotum smooth and shining to moderately granulate, weakly shining ( Figures 101–103 ).

Measurements — holotype (n = 7 + 5 paratypes). HL 1.70 (1.42–1.73); HW 1.74 (1.48–1.79); MOD 0.39 (0.32– 0.39); OMD 0.42 (0.33–0.45); SL 1.27 (1.00–1.32); PNW 1.13 (0.98–1.18); HFL 1.70 (1.49–1.77); ML 1.98 (1.56– 2.07); PW 0.42 (0.38–0.44); PPW 0.59 (0.56–0.63). Indices: SI 72.99 (67.57–80.13); CI 102.35 (96.89–108.64); OI 22.41 (20.11–23.08); HFI 97.70 (96.65–105.13).

Description. Head subquadrate to wider than long (CI = 96.89–108.64), widest just posterior to eyes; posterior margin flat to weakly convex in full-face view. Longitudinal rugae on cephalic dorsum prominent, in full-face view, medial rugae continuing to posterior margin of head or diverging toward posterior corners of head. Interrugae on cephalic dorsum moderately to strongly granulate, weakly shining to dull; posterior corners rugose, interrugae smooth and shining to weakly granulate, weakly shining. Anterior margin of clypeus concave, dorsum with numerous subparallel, longitudinal rugae. Numerous long, curved, bristle-like, cream to light yellowish macrochaetae project from anterior margin of clypeus and basolateral margin of mandibles. Mandibles with six teeth, rarely with an additional denticle between the fourth and fifth teeth; mandibular dorsum coarsely rugose. MOD ranging from 0.20–0.24× HL. In profile, eyes situated slightly anterior to middle of head, OMD = 0.97–1.36× MOD. In full-face view, eyes protruding slightly beyond lateral margins of head. Antennal scapes (SI = 67.57–80.13) failing to reaching posterior corner of head by less than length of basal funicular segment; scapes with weak to moderately strong longitudinal striae, weakly shining to shining; basal flange well developed, flattened with carinate margin. Psammophore well developed.

Mesosomal profile weakly to moderately convex; all mesosomal surfaces with prominent subparallel, regular to irregular rugae to rugoreticulate-vermiculate. In dorsal view, humeral shoulders of pronotum enlarged, weakly to moderately angulate. Dorsum of promesonotum with moderately regular to strongly irregular longitudinal rugae that continue to anterior margin of pronotum or diverge toward humeral shoulders of pronotum; anterior margin of pronotum occasionally with one to several irregular transverse rugae. Irregular rugae on pronotal sides traverse ventrally or posterad or rugoreticulate; rugae on mesopleura angle posterodorsally; irregular transverse rugae on dorsum of propodeum traverse ventrally or anteroventrally on sides. Promesonotal suture absent to weakly impressed. Superior propodeal spines consist of tubercles, denticles, short teeth, or occasionally moderately long to long spines, bases connected by well defined keel; inferior propodeal spines wider than high, apex broadly rounded to weakly acuminate, inferior spines usually as long as to longer than superior spines. Propodeal spiracles narrowly ovate facing posterad. Interrugae on mesosoma smooth and shining to moderately granulate, weakly shining. Legs smooth and shining to weakly coriarious, weakly shining to shining.

Peduncle of petiole about 0.8× as long as petiolar node, anteroventral margin with poorly developed, broadly rounded process. In profile, posterior surface of petiolar node weakly convex; node asymmetrical with anterior surface notably longer than posterior surface, apex subangulate to angulate. In dorsal view, petiolar node longer than wide, widest near spatulate anterior margin, gradually narrowing posterad. Posterior surface of petiolar node with regular to wavy transverse rugae. Dorsum of postpetiole convex in profile; in dorsal view, widest at/near posterior margin, narrowing to anterior margin, maximum width and length about equal. Transverse to weakly arcuate rugae on dorsum of postpetiole finer, denser than those on posterior surface of petiolar node; interrugae on posterior surface of petiolar node and dorsum of postpetiole smooth and shining to weakly coriarious, weakly shining. First gastral tergum with longitudinal striae that extend over anterior one-half or more of segment, posterolateral margins smooth and shining to moderately coriarious, weakly shining.

Erect, short to medium-length, white pilosity moderately abundant on head, longest hairs along posterior margin, rest of hairs rarely> 0.3× 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, gastral terga with moderately dense, erect, white setae, longest on mesosoma and petiolar node, length usually 0.4–0.5× MOD. Color is highly variable, even within a colony. Most commonly, head, mesosoma, petiole, postpetiole blackish to black; gaster dark ferruginous orange to blackish orange, anterior margin of first gastral tergum and posterior margin of all terga sometimes blackish. Other observed color patterns include: (1) head ferruginous orange, reddish-orange to dark reddish-black with rest of body black, and (2) concolorous black ( Figures 101–103 ).

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, (2) striae cover more than anterior one-half of first gastral tergum, (3) head and mesosoma black, gaster ferruginous orange to orangish-black with blackish to black transverse band across posterior margin of terga and sterna, base of first gastral tergum sometimes blackish or body concolorous black, (4) hairs along posterior margin of first and second gastral terga shorter, longest hairs usually <MOD, and (5) dorsum of propodeum with 7–12 narrowly-spaced transverse rugae ( Figure 104 ).

Measurements —(n = 6 paratypes). HL 1.70–1.86; HW 1.83–1.96; MOD 0.36–0.42; OMD 0.40–0.48; SL 1.22–1.39; PNW 1.38–1.51; HFL 1.66–1.90; ML 2.37–2.73; PW 0.40–0.55; PPW 0.71–0.80. Indices: SI 62.56– 72.13; CI 102.23–108.33; OI 19.67–21.69; HFI 90.71–96.94.

Description. With caste-specific morphology of the mesosoma related to wing-bearing and presence of ocelli on head. In full-face view, head subquadrate to wider than long (CI = 102.23–108.33), widest just posterior to eyes, posterior margin flat. Longitudinal rugae on cephalic dorsum prominent, wavy; in full-face view, medial rugae not diverging to weakly diverging toward posterior corners of head; interrugae moderately to strongly granulate, with a beaded appearance; posterior corners rugose, interrugae weakly granulate-punctate, weakly shining. Mandibles with six to seven teeth, dorsal surface coarsely rugose. Psammophore well developed.

All mesosomal surfaces with subparallel, regular to weakly irregular rugae, rugae sometimes irregular to rugoreticulate on pronotal sides; dorsum of propodeum with 7–12 closely spaced transverse rugae; interrugae weakly to moderately granulate-punctate, weakly shining, interrugae on pronotal sides usually more strongly granulate; superior propodeal spines consist of short, triangular teeth to moderately long, tapered, acuminate spines; inferior propodeal spines moderately well developed, wider than tall, apex weakly rounded. Peduncle of petiole about 0.8× as long as petiolar node, ventral margin flat. In profile, petiolar node asymmetrical with anterior surface shorter than posterior surface, apex angulate. Posterior surface of petiolar node with wavy transverse rugae. In dorsal view, dorsum of 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 weakly granulate-punctate, weakly shining. Striae extend over more than anterior one-half of first gastral tergum. Most body surfaces with moderately abundant suberect to erect, short to long, yellowish setae; longest hairs along posterior margin of first and second gastral terga usually shorter than MOD. Head, mesosoma, petiole, postpetiole black; gaster ferruginous orange to orangish-black, with blackish to black transverse band across posterior margin of terga and sterna, base of first gastral tergum sometimes blackish or body concolorous black ( Figure 104 ).

Male diagnosis. Males of this species are diagnosed by the following combination of features: (1) striae extend over more than anterior one-half of first gastral tergum, (2) in profile, rugae forming circumocular whorls posterior to eyes, (3) notauli absent, and (4) head and mesoscutellum black ( Figure 105 ).

Measurements —(n = 8 paratypes). HL 0.95–1.31; HW 1.10–1.33; MOD 0.40–0.49; OMD 0.15–0.21; SL 0.36–0.43; HFL 1.49–1.75; ML 2.09–2.65; PW 0.46–0.53; PPW 0.64–0.80. Indices: SI 30.83–35.83; CI 101.53– 117.86; OI 35.04–37.12; HFI 117.29–150.00.

Additional material examined. ARGENTINA: Chubut: Cerro Dragón , 730 m, Jan 10–15, 2013 ( RAJC) ; Rt 3 at 10.0 km N Jct Rt 37, 2060’, Feb 16, 2014 ( RAJC) ; Rt 37 at 34.9 km SW Jct Rt 3, 2190’, Feb 19, 2014 ( RAJC) ; Rt 25 at 107.1 km WSW Dolavon , 1090’, Feb 21, 2014 ( RAJC) ; Rt 25 at 11.4 km E Las Plumas , 1280’, Feb 21, 2014 ( RAJC) ( Figure 100B ).

Etymology. The specific epithet, varicolor (from Latin, varius = different, varying, and color = color), is derived from the variable color patterns displayed by workers of this species, both within and across colonies.

Discussion. Morphology of P. varicolor is highly variable in terms of color, length of superior propodeal spines, and patterning of rugae on the mesosoma. In regard to color, nests can contain workers with a black head and mesosoma and a ferruginous orange to blackish-orange gaster, while other colonies contain workers with multiple color patterns. Color is a diagnostic character used to identify P. varicolor , and because of this variability workers key out in two separate couplets.

Pogonomyrmex varicolor is not known to co-occur with any other P. rastratus -group species, but additional collecting may show it co-occurs with P. carbonarius , P. sanmartini , and other congeners. The most common color morph is head and mesosoma blackish to black, occasionally with a weak orangish infusion on dorsum of promesonotum; gaster light to dark ferruginous orange to orangish-black. This coloration combined with striae on first gastral tergum extending over more than anterior one-half of segment separate P. varicolor from all congeners except P. catanlilensis , P. forelii , and P. granulatus .

Pogonomyrmex varicolor can be distinguished from P. catanlilensis based on: (1) smaller (HW = 1.48–1.79 mm; PNW = 0.98–1.18 mm; ML = 1.56–2.07 mm), (2) in dorsal view, rugae on promesonotum regular to wavy, longitudinal rugae on mesonotum continue to anterodorsal margin of pronotum or diverge to humeral shoulders of pronotum with one to few transverse rugae along anterodorsal margin, (3) interrugae on promesonotum smooth and shining to moderately granulate, weakly shining, and (4) striae on first gastral tergum longitudinal. In P. catanlilensis : (1) larger (HW = 1.67–2.04 mm; PNW = 1.15–1.42 mm; ML = 2.01–2.76 mm), (2) in dorsal view, longitudinal rugae on mesonotum weakly to strongly irregular, often nearly rugoreticulate; rugae on pronotum usually rugoreticulatevermiculate, (3) interrugae on promesonotum usually moderately to strongly granulate, weakly dull to dull, and (4) some to most striae on first gastral tergum usually oblique and/or transverse. Pogonomyrmex varicolor can be distinguished from P. forelii based on the superior propodeal spines. In P. varicolor , the superior propodeal spines consist of tubercles, denticles, short teeth, or rarely moderately long to long spines, with a length <0.5× the distance between their bases for some to all workers in a series. In P. forelii , the superior propodeal spines are consistently moderately long to long, with a length> 0.6× the distance between their bases. Pogonomyrmex varicolor can be distinguished from P. granulatus based on the following characters: (1) superior propodeal spines consist of short to long spines for some workers in a series, (2) in profile, rugae posterior to eyes fine, dense, regular, converging at or near posterior corners, and (3) interrugae on cephalic dorsum smooth and shining to moderately coriarious, weakly shining, rarely with a beaded appearance. In P. granulatus : (1) superior propodeal spines consist of tubercles, denticles, or short blunt teeth, (2) in profile, rugae posterior to eyes coarse, irregular, sometimes circumocular or converging anterior to posterior corners, and (3) interrugae on cephalic dorsum strongly granulate, weakly dull to dull, with a beaded appearance. Pogonomyrmex varicolor might also be confused with P. mendozanus and P. pronotalis because of the similar color pattern. However, the first gastral tergum lacks striae in both species, whereas longitudinal striae are present in P. varicolor .

Other color variants of P. varicolor include head and/or gaster ferruginous orange to dark reddish-black to blackish-orange, mesosoma usually blackish to black or occasionally concolorous black. Bicolored workers can be distinguished by the combination of: (1) striae on first gastral tergum extending over more than anterior one-half of segment, (2) all striae on first gastral tergum longitudinal, (3) posterolateral margins of first gastral tergum usually smooth and shining to strongly shining, (4) rugae on dorsum of promesonotum usually wavy, irregular, or rugoreticulate, and (5) superior propodeal spines consist of denticles, tubercles or short teeth, rarely long spines. These characters distinguish P. varicolor from all congeners except for P. carbonarius and P. strioligaster , while series that contain only concolorous black workers might be confused with P. atratus and P. sanmartini . Pogonomyrmex varicolor is distinguished from P. strioligaster by: (1) some workers typically have other color patterns, and (2) superior propodeal spines consist of denticles to short teeth, rarely long spines. In P. strioligaster : (1) head and gaster ferruginous orange for all workers in a series, part to all of mesosoma black, and (2) superior propodeal spines long, length>0.6× the distance between their bases. Pogonomyrmex varicolor is distinguished from P. carbonarius based on the posterolateral margins of the first gastral tergum, which are usually smooth and shining in P. varicolor , while they are moderately to strongly coriarious, dull to weakly shining in P. carbonarius . However, in some colonies of P. varicolor the posterolateral margin of the first gastral tergum is moderately coriarious, weakly shining. In these cases, P. varicolor is distinguished by one or more workers with a black head and mesosoma and rugae on posterior surface of petiolar node and dorsum of postpetiole regular to wavy and interrugae usually smooth and shining. In P. carbonarius , workers with a black head and mesosoma are lacking, rugae on posterior surface of petiolar node and dorsum of postpetiole often irregular to very irregular and interrugae usually granulate, weakly shining to dull. Concolorous black workers of P. atratus lack striae on the first gastral tergum, whereas P. varicolor have longitudinal striae that extend over the anterior one-half or more of the segment. In P. sanmartini , striae extend over more than anterior one-half of first gastral tergum, but some to most of these striae are oblique to transverse, whereas all striae are longitudinal in P. varicolor .

Biology. Pogonomyrmex varicolor workers are solitary foragers. Nests of P. varicolor are commonly placed at the base of a grass clump, but they also occur in open, exposed sites. Nests were in sandy-loamy-gravelly soils to sandy-gravelly-rocky soils, and they often lacked a tumulus or the tumulus ranged up to 5–15 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 more than 2000 workers. Sexuals have been collected on February 19, indicating that mating flights occur during the austral summer.

Pogonomyrmex varicolor inhabits sites at elevations from 330–730 m in the Patagonian steppe and Low Monte ecoregions, as defined by Olson et al. (2001) ( Figure 100B ).

Figures

FIGURE 100. Geographic distribution of: (A) Pogonomyrmex tafi, (B) P. varicolor, and (C) P. vermiculatus. The large black circle in each panel denotes the type locality.

FIGURE 101. Photographs of Pogonomyrmex varicolor holotype worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922468). Workers of P. varicolor are highly variable: photographs show the typical bicolored worker (head and mesosoma black, gaster dark orangish-black) with superior propodeal spines consisting of short, triangular teeth. Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 102. Photographs of Pogonomyrmex varicolor paratype worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922470). Workers of P. varicolor are highly variable: photographs show the less common concolorous black color pattern with short superior propodeal spines. Photographs by Michele Esposito from www. AntWeb.org.

FIGURE 103. Photographs of Pogonomyrmex varicolor paratype worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922471). Workers of P. varicolor are highly variable: photographs show the less common bicolored pattern (head and gaster dark reddish, mesosoma black) with superior propodeal spines consisting of short, triangular teeth. Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 104. Photographs of Pogonomyrmex varicolor paratype alate queen: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922467). Photographs by Michele Esposito from www.AntWeb.org.

FIGURE 105. Photographs of Pogonomyrmex varicolor paratype male: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT0922469). Photographs by Michele Esposito from www.AntWeb.org.