Pogonomyrmex magnacanthus Cole, 1968

Johnson, Robert A., Overson, Rick P. & Moreau, Corrie S., 2013, A New Species of Seed-harvester Ant, Pogonomyrmex hoelldobleri (Hymenoptera: Formicidae), from the Mohave and Sonoran Deserts of North America, Zootaxa 3646 (3), pp. 201-227 : 205-213

Pogonomyrmex magnacanthus Cole

( Figures 1–2 , 4–5 )

Pogonomyrmex (Pogonomyrmex) magnacanthus Cole, 1968 [part]: 133, pl. 2, fig. 5; pl. 3, fig. 12; pl. 4, fig. 10; pl. 6, fig. 9; pl. 7, fig. 16; pl. 8, fig. 10; pl. 11, fig. 10 (worker, queen, male). Holotype examined [LACM, Cole No. Cal-378]; Palm Springs, California, USA (by A.C. Cole, Jr., on 8 August, 1960); Taber, Cokendolpher & Francke, 1988: 51 (karyotype) (2 n = 32). See also Ward (2005).

Worker

Diagnosis. Pogonomyrmex magnacanthus is a small species (HW = 1.15–1.80 mm) that is identified by: (1) its unusually large eyes (MOD = 0.33–0.49 mm; OI = 27.22–33.61; malar ratio (MOD/OMD) usually <1.0) (see Figures 1–3 ). OI is the most reliable character to identify P. magnacanthus given that MOD is positively associated with HW such that it sometimes overlaps with that of other species (see Figure 3 ). Cole (1968) also listed an unusually large eye and a high ocular index as diagnostic characters for P. magnacanthus . Interestingly, the holotype that Cole selected was somewhat of an outlier for both characters because the eye was relatively small and the OI was lower than that of other paratype workers (see below and Cole, 1968).

Measurements (mm)— holotype (n = 25 paratypes, all from the type locality at Palm Springs, California [CAL- 356, CAL-374, CAL-378, CAL-380, CAL-381, CAL-382], plus 37 non-type workers). HL 1.37 (1.17–1.65); HW 1.38 (1.15–1.80); MOD 0.39 (0.33–0.49); OMD 0.39 (0.31–0.46); SL 1.02 (0.86–1.15); PNW 0.88 (0.73–1.08); HFL 1.38 (1.08–1.74); ML 1.67 (1.28–1.91); PW 0.36 (0.28–0.45); PPW 0.54 (0.40–0.60). Indices: SI 74.45 (63.89–81.67); CI 99.28 (92.54–112.21); OI 28.47 (27.22–33.61); HFI 100.73 (88.00–112.50).

Description. Head subquadrate to quadrate (CI = 92.54–112.21), broadest just posterior to eye; posterior margin flat in full-face view. Longitudinal cephalic rugae prominent, in full-face view median rugae diverging toward posterior corners near posterior margin of head. In side view, rugae converging immediately posterior to eyes to form indistinct to well defined circumocular whorls that often weaken toward vertex, or rugae converging toward vertex, or circumocular whorls and rugae mostly absent posterior to eye and weakly to densely granulatepunctate, dull to sub-shining, especially toward vertex. Vertex rugose, densely granulate, or occasionally smooth to weakly striated, dull to shining. Cephalic interrugal spaces weakly to moderately granulate-punctate on anterior portion of head, often becoming more strongly granulate-punctate on posterior half of head, sub-shining to shining. Anterior margin of clypeus flat to weakly concave. Mandible with seven teeth; mandibular dorsum coarsely striate. In profile, eyes large, MOD ranging from 0.27–0.32x HL, OI = 27.22–33.61, MR usually <1.0; eye situated near middle of head. Antennal scapes moderately long (SI = 63.89–81.67), failing to reach vertex by length of basal funicular segment. Basal flange of antennal scape flattened and well developed, margin weakly carinate. Psammophore well developed.

Mesosomal profile convex. All mesosomal surfaces with prominent parallel/subparallel rugae. Dorsum of promesonotum with transverse rugae that curve obliquely to posterior, often becoming indistinct on pronotal sides. Mesopleura with subparallel rugae angling posterodorsally. Propodeum lacking spines or teeth, occasionally with minute denticles; in side view, juncture of propodeum and propodeal declivity evenly convex to weakly angulate; rugae on dorsum of propodeum transverse, declivitous face often with one or two discontinuous to continuous transverse rugae, interrugal spaces smooth and shining. Propodeal spiracles narrowly ovate. Interrugal spaces on mesosoma moderately granulate-punctate, sub-shining to smooth and shining; interrugal spaces on pronotal sides moderately to densely granulate, dull. Legs moderately to strongly shining.

Petiolar peduncle long, ventral margin straight. In side view, posterior face of petiole weakly convex; petiolar node asymmetrical with anterior surface shorter than posterior surface. Apex of node weakly to moderately angulate. In dorsal view, petiolar node longer than broad, sides subparallel or diverging slightly toward the smoothly rounded to weakly angulate anterior margin. Sides and dorsum of petiolar node moderately to strongly granulate-punctate, dull to sub-shining, occasionally with several longitudinal to oblique rugae that are restricted to posterior one-third of petiole. 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, moderately granulate-punctate, dull to sub-shining. Gaster smooth and strongly shining.

Erect to suberect white pilosity moderately abundant on head, short to medium in length, often with one to few longer hairs, none exceeding MOD. Moderately abundant semidecumbent to decumbent pilosity on scape with occasional suberect hairs, abundant semidecumbent to decumbent hairs on funicular segments. Legs with moderately abundant suberect to semidecumbent white setae. Mesosoma, petiole, and postpetiole with a lower density of mostly long, flexuous hairs mostly concentrated on dorsal surfaces, longest distinctly shorter than MOD; gastric tergites with moderately abundant, medium length suberect hairs. Entire body concolorous light to dark ferruginous orange ( Figure 1 ).

Queen

Diagnosis. As in worker diagnosis, but with caste-specific morphology of the mesosoma related to wing-bearing, presence of small ocelli on the head, and as illustrated in Figure 4 . Mandible with seven teeth; cephalic rugae forming circumocular whorls. Eyes large (OI = 29.35–35.29), MR <1.00, MOD ranging from 0.30–0.35x HL. All mesosomal surfaces with prominent rugae.

Measurements (mm)—(n = 3). HL 1.79–1.88; HW 1.84–1.95; MOD 0.54–0.66; OMD 0.40–0.58; SL 1.22– 1.26; PNW 1.40–1.45; HFL 1.73–1.90; ML 2.61–2.75; PW 0.56–0.62; PPW 0.82–0.93. Indices: SI 64.62–66.30; CI 99.47–107.73; OI 29.35–35.29; HFI 94.02–100.00.

Description. As in worker diagnosis, but with caste-specific structures related to wing-bearing, presence of small ocelli on head, and as illustrated in Figure 4 . Small, only slightly larger than conspecific workers. In full-face view, head quadrate to slightly broader than long, posterior margin flat, median rugae diverging toward posterior corners near posterior margin of head. Dorsum and sides of head conspicuously rugose, in side view rugae forming circumocular whorls posterior to eyes, interrugal spaces mostly smooth and shining. Mandible with seven teeth, dorsal surface coarsely rugose, strongly shining. Eyes large (OI = 29.35–35.29), MR <1.00, MOD ranging from 0.30–0.35x HL. Base of scape not flattened; superior and inferior lobes poorly developed, no wider than width of base of scape.

All mesosomal surfaces with prominent subparallel/parallel rugae, those on mesoscutum and mesoscutellum fine, parallel, and longitudinal; interrugal spaces smooth and shining. In side view, propodeum unarmed, juncture of propodeum and propodeal declivity slightly angulate, sides and dorsal surface transversely or obliquely rugose, declivitous surface smooth and strongly shining. Petiolar peduncle long, ventral margin straight. In side view, petiolar node asymmetrical with anterior surface shorter than posterior surface. Apex of node rounded. In dorsal view, petiole length and width similar to slightly longer than wide; posterior face finely rugose, interrugal spaces weakly coriarious, sub-shining. Postpetiole broader than long; posterior portion finely rugose, interrugal spaces weakly coriarious, sub-shining; anterior portion granulate-punctate. Gastric tergites weakly coriarious and subshining to smooth and shining. Most body surfaces with moderately abundant coarse suberect to erect setae. Entire body concolorous light to dark ferruginous orange.

Male

Diagnosis. Mandible with four teeth on suboblique cutting margin. Mandibular dorsum with faint rugae/striae, mostly sub-shining. Anterior margin of clypeus moderately concave, lateral lobes distinct, broadly rounded; antennal scapes with faint rugae/striae, sub-shining, or lacking sculpture, smooth and shining. Eye unusually large (MOD> 0.53, OI> 42.5, MR <0.34) ( Figure 5 ).

Measurements (mm)—(n = 4). HL 1.09–1.29; HW 1.20–1.36; MOD 0.53–0.59; OMD 0.15–0.19; SL 0.43– 0.57; HFL 1.53–1.66; ML 2.29–2.54; PW 0.52–0.61; PPW 0.70–0.82. Indices: SI 32.09–41.91; CI 104.69–111.82; OI 42.54–44.17; HFI 120.59–130.08.

Description. Mandible with four teeth on suboblique cutting margin; basal tooth sometimes weakly bifid; basal tooth not offset; mandibular dorsum as described above. Clypeus lacking sculpture, mostly smooth and shining except for scattered punctures, anterior margin moderately concave, lateral lobes distinct, broadly rounded. Antennal scapes reaching to or near posterior margin of eye, mostly smooth and shining to faintly striate. Parallel/ subparallel cephalic rugae fine and close, slightly wavy, interrugae weakly punctate, sub-shining.

In profile, anterior face of mesonotum forming a mostly straight line with pronotum, slightly less than one-half as long as dorsal surface. In side view, juncture between propodeum and propodeal declivity subangulate, without spines or denticles. Sides of pronotal collar smooth and shining; katepisternum mostly smooth and shining with scattered foveae, posterior margin often faintly striate, shining. Mesonotum shiny with piligerous punctures, notauli very weakly impressed. Propodeum smooth and shining. Ventral margin of petiolar peduncle straight. In side view, petiolar node broadly rounded, anterior surface longer than posterior surface, forming a mostly straight continuous to slightly curved profile with dorsal margin of petiolar peduncle. Dorsal surface of petiole smooth and shining with scattered punctures to microrugoreticulate, sub-shining. Postpetiole broader than long, dorsal surface mostly smooth, sub-shining to shining. Head, mesosoma, petiole, and postpetiole with moderately abundant flexuous white hairs, often similar in length to MOD. Gastric tergites smooth and shining, hairs shorter and less dense than on rest of body. Entire body a concolorous ferruginous orange to brownish-orange ( Figure 5 ).

Additional material examined. UNITED STATES: Arizona: La Paz Co.: 3.5 mi SE Parker on Hwy 95, 460’, Apr 4, 1997, SP Cover SPC#4830 (6w, MCZ), SPC#4834 (8w, MCZ). Maricopa Co.: Sentinel, Jul 9, 1956, AC Cole AZ-404 (9w PARATYPES, LACM), AZ-405 (9w PARATYPES, LACM), AZ-406 (9w PARATYPES, LACM). Yuma Co. : Blaisdell, 200’, Oct 26, 1952, #406 (6w, LACM); Dateland, Apr 21, 1994, RA Johnson RAJ#481 (4w, RAJC), RAJ#482 (6w, RAJC); 0.5 mi S Dateland, Sep 18, 1992, RA Johnson RAJ#103-1 (2w, RAJC); Mohawk Dunes at 9.7 mi E Tacna, Mar 21, 2001, RA Johnson RAJ#2235 (3w, RAJC); NE end of Mohawk Dunes, 460’, Jun 24, 2009, RA Johnson RAJ#4248 (6w, RAJC), RAJ#4249 (3w, RAJC), RAJ#4250 (9w, RAJC); I-8 at 1.0 mi E Dome Valley, 250’, Apr 26, 2012, RA Johnson RAJ#4920 (3w, RAJC); Hwy 95 at Yuma Proving Grounds , 250’, Apr 27, 2012, RA Johnson RAJ#4922 (3w RAJC). California: Imperial Co. : 15 mi E Holtville, Jul 27, 1961, AC Cole CAL-395 (16w, LACM); 13.5 mi E Holtville, Jul 31, 1960, AC Cole CAL-359 (12w PARATYPES, LACM); CAL-360 (15w PARATYPES, LACM); 19 mi W Winterhaven, Jul 28, 1959, AC Cole CAL-336 (8w PARATYPES, LACM), CAL-335 (11w PARATYPES, LACM); 7 mi W Winterhaven, Jul 28, 1959, AC Cole CAL-333 (13w PARATYPES, LACM); Glamis, Mar 28, 1964, Saul Frommer (2w, LACM); Algodones Dunes at 15.5 mi NNW Glamis, 180’, Mar 31, 1997, RA Johnson #945 (6w, RAJC). Riverside Co.: 14.5 mi N Midland (site) ca 34o 02.5’N 114o 52’W, sand dunes, Apr 9, 1994, RR Snelling #94-12b (2w, LACM); Palm Springs, Jun 16, 1963, AC Cole CAL-424 (4w, 2aq PARATYPES, LACM), CAL-425 (1w, 1aq, 1m PARATYPES, LACM); Aug 8, 1960, CAL-356 (51w PARATYPES, LACM), CAL-374 (9w PARATYPES, LACM), CAL-375 (6w PARATYPES, LACM), CAL-376 (29w PARATYPES, LACM), CAL-377 (9w PARATYPES, LACM), CAL- 378 (30w PARATYPES, LACM), CAL-379 (6w PARATYPES, LACM), CAL-380 (9w PARATYPES, LACM), CAL-381 (9w PARATYPES, LACM), CAL-382 (21w PARATYPES, LACM); 7.5 mi NE Desert Center (33.79’N, 115.30’W), Apr 11, 2004, RR Snelling #04-002 (8w, LACM); Palm Desert, Bob Hope & Gerald Ford Dr, May 15, 1997, RA Johnson RAJ#1005 (3w, RAJC), RAJ#1006 (12w, RAJC); 20 mi W Blythe, May 5, 1963, RR Snelling (3w, LACM); 3 mi E Mecca, 100’, Mar 26, 1986, RR Snelling (10w, 2m, LACM). San Bernardino Co.: 3 mi SSW Rice (34.04’N, 114.87’W), Apr 11, 2004, RR Snelling #04-004 (7w, LACM); 2 mi W Rice, 1000’, Oct 12, 1963, RR Snelling (6w, LACM); Cadiz Dunes, Apr 25, 1978, AR Hardy & FG Andrews (2w, 1m, LACM); 29 Palms, 2000’, Nov 6, 1967, RR Snelling #67-290 (3w, LACM); Johnson Valley, May 15, 2008, RA Johnson RAJ#4126 (6w, RAJC); 4 km S Kelso, 670 m, Mar 29, 2004, PS Ward PSW#15179 (3w, MCZ); 2.8 mi NW Pisgah Crater, 2110’, Apr 5, 2010, RA Johnson RAJ#4483 (6w, RAJC), RAJ#4484 (6w, RAJC), RAJ#4485 (6w, RAJC). San Diego Co.: Anza Borrego State Park, 5.0 mi S Split Mountain, 850’, Apr 2, 1997, GC Snelling #98-052 (6w, RAJC), RA Johnson RAJ#955-1 (12w, RAJC), RAJ#951 (6w, RAJC), SP Cover SPC#4811 (6w, MCZ), SPC#4812 (6w, MCZ). MEXICO: Baja California: Hwy 5 at 1 mi S Laguna Salada, May 10, 1998, RA Johnson RAJ#BC- 1373 (9w, RAJC), RAJ#BC-1374 (8w, RAJC; 3w UCDC); Hwy 5 at 17.5 mi SE San Felipe, Feb 27, 1992, RA Johnson RAJ#BC-43 (6w, RAJC). Sonora: 11.5 mi E Puerto Peñasco, 50’, Jul 17, 2009, RA Johnson RAJ#4275 (6w, RAJC), RAJ#4276 (9w, RAJC), RAJ#4277 (6w, RAJC), RAJ#4280 (9w, RAJC); 16 mi E Puerto Peñasco, 30’, Jul 16, 2009, RA Johnson RAJ#4272 (6w, RAJC).

Etymology. The specific epithet, magnacanthus (from Latin, magna for great or large, and Greek, kanthos, for corner of the eye), likely refers to the greatly enlarged corner of the eye in this species. In describing this species, Cole discussed the unusually large eyes but made no mention in regard to the corners of the eyes.

Discussion. Pogonomyrmex magnacanthus is most likely to be confused with P. hoelldobleri , as evidenced by the numerous series of the latter species (including several paratype series) that A.C. Cole misidentified as P. magnacanthus . The significantly larger eye (MOD and OI) separates P. magnacanthus from P. hoelldobleri ( Figures 2–3 ), but OI is the more diagnostic character because it is consistently higher for P. magnacanthus (OI = 27.22–33.61) than for P. hoelldobleri (OI usually <27.50)( Figure 3 ). Additionally, the malar ratio is usually <1.0 for P. magnacanthus , while this ratio is usually> 1.05 for P. hoelldobleri ( Figure 3 ).

Pogonomyrmex magnacanthus occurs sympatrically with P. californicus , but it has a low likelihood of cooccurring with P. maricopa and P. mohavensis . Two other P. californicus group species (P. a n z e n s i s and P. snellingi ) also occur in the Sonoran Desert, but it is doubtful that P. magnacanthus occurs sympatrically with either species; P. anzensis inhabits unproductive, rocky hillsides that are unlike any sites known to be occupied by P. magnacanthus , while P. snellingi is well removed from the probable geographic distribution of P. magnacanthus . Pogonomyrmex magnacanthus can be distinguished from all of these species using the characters described above.

Figures

FIGURE 1. Photograph of Pogonomyrmex magnacanthus Cole—HOLOTYPE worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body.

FIGURE 2. Photographs of diagnostic characters to distinguish between workers of P. magnacanthus Cole and those of P. hoelldobleri Johnson, Overson & Moreau and P. m o h a v e n s i s Johnson. Photograph of P. magnacanthus PARATYPE worker: (A) eye and malar area (MOD = 0.44, OI = 29.5, MR = 0.98), and circumocular whorls indistinct to absent, moderately granulate toward vertex, and (B) circumocular whorls present. Photograph of P. hoelldobleri worker: (C) eye and malar area for HOLOTYPE worker (MOD = 0.36, OI = 23.2, MR = 1.17), and absence of circumocular whorls—rugae converging near vertex, and (D) absence of circumocular whorls—area posterior to eyes with faint rugae. Photograph of P. m o h a v e n s i s worker: (E) eye and malar area for PARATYPE worker (MOD = 0.33, OI = 21.7, MR = 1.36), and absence of circumocular whorlsrugae extending to vertex, with rugae becoming weak to absent on / near vertex, and (F) absence of circumocular whorls—rugae extending to vertex; vertex rugose.

FIGURE 3. Bivariate plots for workers: (A) maximum eye diameter versus head width, (B) ocular index versus head width, and (C) malar ratio versus head width (n = 63 for P. magnacanthus Cole, n = 59 for P. hoelldobleri Johnson, Overson & Moreau, plus 16 PARATYPE workers of P. magnacanthus that do not belong to the latter species [see text], n = 25 for P. mohavensis Johnson). Non-type workers were selected to represent the geographic range of each species.

FIGURE 4. Photograph of Pogonomyrmex magnacanthus Cole alate queen: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body.

FIGURE 5. Photograph of Pogonomyrmex magnacanthus Cole male: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body.