Pogonomyrmex hoelldobleri

Pogonomyrmex hoelldobleri is very similar to Pogonomyrmex magnacanthus and before its description was often identified as the latter.

Identification
Johnson et al. (2013) - Worker. Pogonomyrmex hoelldobleri is characterized by: (1) eye not unusually large (MOD usually < 0.42, OI usually < 27.50, MR usually > 1.05, (2) mandible with seven teeth, (3) cephalic rugae converge posterior to eyes, usually near vertex, but not forming circumocular whorls, (4) interrugal spaces on pronotal sides moderately to strongly granulate, dull to weakly shining, and (5) gaster concolorous with head and mesosoma.

Queen. As in worker diagnosis, but with caste-specific structures related to wing-bearing and presence of small ocelli on head. Mandible with seven teeth. Eye not unusually large (MOD < 0.45, OI < 28.50, MR usually > 1.05). All mesosomal surfaces except for mesoscutum and mesoscutellum with prominent rugae; sculpturing absent on mesoscutum and mesoscutellum except for scattered punctures and occasional faint longitudinal striae. Posterior face of petiole and dorsum of postpetiole weakly to moderately granulate or with weak tranverse rugae. Base of scape rounded; superior and inferior lobes poorly developed, no wider than width of scape base.

Male. Mandible with four teeth on suboblique cutting margin. Mandibular dorsum, clypeus, and antennal scapes lacking sculpture (mandibular dorsum occasionally with faint striae), mostly smooth and shining except for scattered punctures; anterior margin of clypeus weakly concave, lateral lobes indistinct. Eye not unusually large (MOD < 0.50, OI < 39.4, MR > 0.38).

Pogonomyrmex hoelldobleri is most likely to be confused with Pogonomyrmex magnacanthus, especially given the large number of series that A.C. Cole erroneously identified as P. magnacanthus. The two species occur sympatrically in several locales. The significantly larger eye (MOD and OI) separates P. magnacanthus from P. hoelldobleri. OI is the best character to separate the two species because it is consistently higher for P. magnacanthus (OI = 27.22-33.61) than for P. hoelldobleri (OI rarely > 27.50). The malar ratio is usually < 1.0 for P. magnacanthus, while this ratio is usually > 1.05 for P. hoelldobleri.

Pogonomyrmex hoelldobleri also occurs in sympatry with Pogonomyrmex californicus and is likely to occur in sympatry with Pogonomyrmex mohavensis, but it has a low likelihood of co-occurring with Pogonomyrmex maricopa. Pogonomyrmex hoelldobleri can be distinguished from P. mohavensis based on the following characters: (1) P. hoelldobleri has seven teeth, (2) the interrugal spaces on the pronotal shoulders are weakly to strongly punctate/granulate, dull to sub-shining, and (3) the cephalic rugae typically converge near the vertex. In P. mohavensis, the mandible has six teeth (a seventh sometimes occurs as a denticle between the basal and sub-basal teeth), interrugal spaces on the pronotal shoulders are smooth and shining, and the cephalic rugae extend more or less directly to the vertex or converge only slightly near the vertex. Two other P. californicus group species (Pogonomyrmex anzensis and Pogonomyrmex snellingi) also occur in the Sonoran and Mohave Deserts, but it is doubtful that P. hoelldobleri occurs sympatrically with either species; P. anzensis occurs in unproductive, rocky hillside habitats unlike any sites that are known to be occupied by P. hoelldobleri, while P. snellingi is well removed from the probable geographic distribution of P. hoelldobleri. Regardless, the absence of circumocular whorls separates P. hoelldobleri from both species.

Distribution
Southern Nevada, southeastern California, southwestern Arizona, northern Baja California, and northwestern Sonora.

Distribution based on Regional Taxon Lists
Nearctic Region: United States.

Biology
Johnson et al. (2013) - The biology of Pogonomyrmex magnacanthus and Pogonomyrmex hoelldobleri appear to be very similar, and are thus discussed together. In both species, the nests are variable and can range from a nest entrance that lacks a tumulus to a tumulus that ranges from 3–15 cm in diameter; the nest entrance commonly lacks a tumulus in P. hoelldobleri. Nests are typically placed in open exposed sites, but can be difficult to locate because of their small size or absence of an external tumulus. In such cases, nests are most easily located by baiting foragers, then following them back to the nest. Workers of both species forage solitarily during the day, harvesting seeds and related items. Colonies of P. magnacanthus contain relatively few workers; Cole (1968) estimated that colony size ranged from 100–225 workers, which accords with observations of the senior author. Colonies of P. hoelldobleri are also small and appear to contain no more than 300–400 workers (R.A. Johnson, pers. obs.).

Reproductive sexuals of P. magnacanthus, P. hoelldobleri, and Pogonomyrmex mohavensis have been collected infrequently (a total of 3 alate queens and 4 males for P. magnacanthus, 8 alate queens and 2 males plus one male pupae for P. hoelldobleri, and 2 alate queens for P. mohavensis); collection dates range from 26 March to 13 June for P. magnacanthus and from 23 April to 5 May for P. hoelldobleri. Mating flights have not been observed for either species, but they are predicted to be similar to those of P. californicus, in which flights are triggered by cues such as photoperiod, temperature, or humidity (but not rain-triggered as in most species of Pogonomyrmex), and they likely take place over several weeks during late spring to early summer (Johnson, 2000). Alate queens of P. mohavensis were collected on 15 September; several nests of P. californicus in the vicinity of this collection also contained alate queens on this date, and these queens were observed outside the nest preparing for their mating flight. Thus, in the central valley area of California, mating flights for P. californicus and P. mohavensis appear to be up to several months later than those in other parts of their geographic ranges.

Both P. magnacanthus and P. hoelldobleri are restricted to hot desert habitats (Wheeler & Wheeler, 1973) in the Mohave and Sonoran Deserts of southeastern California, western Arizona, northwestern Sonora, Mexico, and the San Felipe Desert of Baja California, Mexico; the range of P. hoelldobleri also extends further north into southern Nevada. Current records indicate that the geographic range of P. magnacanthus is more restricted than previously believed (Figure 11), especially given that this study transferred all Nevada records (see Wheeler & Wheeler, 1986) to P. hoelldobleri (see below). Pogonomyrmex magnacanthus inhabits sites at elevations that range from approximately 5–855 m, while P. hoelldobleri is known from elevations that range from 0–1350 m. The two species have broadly overlapping geographic distributions and occur in sympatry at several locales (Figure 11), but preferred microhabitat differs for the two species. Pogonomyrmex magnacanthus is largely restricted to sand dunes, interdune habitats, and other areas with a loose sand substrate (Cole, 1968; Johnson, 2000), whereas P. hoelldobleri sometimes occurs in loose sandy soils, but it is most common in relatively compact sandy or gravelly alluvial soils.

Nomenclature

 *  hoelldobleri. Pogonomyrmex hoelldobleri Johnson, Overson & Moreau, 2013: 213, figs. 2, 6-8 (w.q.m.) U.S.A.

Worker
(mm)—holotype (n = 75 [15 paratypes, 43 non-types, 16 P. magnacanthus Paratypes]). HL 1.57 (1.24–1.76); HW 1.55 (1.17–1.84); MOD 0.36 (0.30–0.42); OMD 0.42 (0.35–0.72); SL 1.20 (0.94–1.34); PNW 0.91 (0.77–1.11); HF 1.67 (1.19–1.89); ML 1.84 (1.35–2.03); PW 0.34 (0.27–0.46): PPW 0.51 (0.38–0.59). Indices: SI 77.42 (66.25–87.18); CI 98.73 (93.98–115.79); OI 23.23 (21.12–29.01); HFI 107.74 (84.97–117.93).

Head subquadrate to quadrate (CI = 93.98–115.79), broadest just posterior to eye; posterior margin flat in full-face view. Longitudinal cephalic rugae prominent, in full-face view median rugae usually diverging toward posterior corners near posterior margin of head. In side view, rugae converging slightly near vertex, occasionally becoming faint between posterior margin of eye and vertex. Vertex faintly to strongly rugose, occasionally mostly smooth to weakly granulate, sub-shining to shining. Cephalic interrugal spaces moderately punctate, sub-shining to smooth and shining. Anterior margin of clypeus slightly concave. Mandible with seven teeth; mandibular dorsum coarsely striate. In profile, eyes not unusually large, MOD ranging from 0.22–0.29x HL, OI = 21.12–29.01, MR usually > 1.05; eye situated near middle of head. Antennal scapes moderately long (SI = 66.25–87.18), failing to reach vertex by less than 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 on pronotal sides, rugae on pronotal sides often slightly less distinct than on other portions of mesosoma; rugae usually oblique to longitudinal on anterior portion of mesonotum. Mesopleura with subparallel rugae angling posterodorsally. Propodeum lacking spines or teeth; in side view, juncture of propodeum and propodeal declivity evenly convex to weakly angulate; rugae on propodeal dorsum transverse, declivitous face 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 usually more densely granulate than other portions of mesosoma. Legs moderately to strongly shining.

Petiolar peduncle long, ventral margin straight. In side view, posterior face of petiole slightly convex; petiolar node asymmetrical with anterior surface slightly shorter than posterior surface. Apex of node weakly to strongly angulate, posterior surface sometimes curved upward near anterior margin. 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 strongly granulate-punctate, dull to sub-shining to smooth and 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, weakly to moderately granulate, 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, 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 longer, flexuous hairs mostly concentrated on dorsal surface, longest distinctly shorter than MOD; gastric tergites with moderately abundant, medium length suberect hairs. Entire body concolorous light to dark ferruginous orange, posterior portion of gaster sometimes slightly darker.

Queen
(mm)—(n = 8). HL 1.36–1.66; HW 1.44–1.79; MOD 0.40–0.45; OMD 0.40–0.50; SL 0.97–1.23; PNW 1.24–1.54; HFL 1.38–1.67; ML 2.18–2.62; PW 0.45–0.57; PPW 0.61–0.73. Indices: SI 65.52–72.12; CI 100.00–114.10; OI 22.47–28.47; HFI 83.64–109.03.

As in worker diagnosis, but with caste-specific structures related to wing-bearing, presence of small ocelli on head. Small, only slightly larger than conspecific workers. In full-face view, head quadrate to broader than long, posterior margin flat. Dorsum and sides of head conspicuously rugose, in side view rugae forming circumocular whorls posterior to eyes or rugae converging near vertex, interrugal spaces smooth and strongly shining. Mandible with seven teeth, dorsal surface coarsely rugose, strongly shining. Eyes not large (OI = 22.47–28.47), MR usually > 1.05, MOD ranging from 0.25–0.30x HL. Base of scape not flattened; superior and inferior lobes poorly developed, no wider than width of base of scape.

Mesosoma as described above, propodeum unarmed; in side view, juncture of propodeum and propodeal declivity rounded to subangulate, sides and dorsal surface rugose or rugae absent near mid-line, shining, posterior 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 moderately to strongly angulate, anterior edge of posterior face sometimes curved upward forming a crest. Postpetiole broader than long. Posterior face of petiole and dorsum of postpetiole weakly to moderately granulate or with weak transverse rugae, sub-shining to shining. Gastric tergites smooth and shining. Most body surfaces with moderately abundant coarse suberect to erect setae. Entire body concolorous light to dark ferruginous orange, except for incomplete to complete darker transverse bands on one or more gastric tergites.

Male
(mm)—(n = 2). HL 1.15–1.25; HW 1.27–1.30; MOD 0.49–0.50; OMD 0.19–0.20; SL 0.54–0.56; HFL 1.43–1.56; ML 2.08–2.26; PW 0.54–0.58; PPW 0.65–0.73. Indices: SI 42.52–43.08; CI 104.00–110.43; OI 37.69–39.37; HFI 112.60–120.00.

Mandible with four teeth on suboblique cutting margin; tip of sub-apical tooth sometimes weakly bifid; basal tooth not offset; mandibular dorsum as described above. Anterior margin of clypeus broadly and shallowly concave, mostly smooth and shining except for scattered punctures, lateral lobes indistinct. Antennal scapes reaching to or near posterior margin of eye, mostly smooth and shining. Cephalic rugae fine and close, slightly wavy to irregular, interrugae weakly punctate, moderately 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 superficially rugoreticulate to punctate-granulate; katepisternum partially to largely covered by very fine wavy to irregular longitudinal striae, sub-shining to shining. Mesonotum shiny with piligerous punctures, notauli weakly impressed. Propodeum mostly smooth and shining to microrugoreticulate, granulate, sub-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 surface 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. Head and mesosoma brownish-orange, gaster a lighter ferruginous orange.

Type Material
Holotype (worker) plus 27 paratypes. UNITED STATES: Arizona: Yuma Co.: 0.2 km S Tacna, 125 m (22o 6.4’S 65o 36.8’W), May 14, 2010, leg. R.A. Johnson #4500. Nests were in Sonoran Desert habitat that was dominated by scattered individuals of Larrea tridentata and Ambrosia dumosa. The holotype is deposited in the. Paratypes (n = 27 workers) all from the same locality and date as the holotype and leg. R.A. Johnson #4500 are distributed as follows: MCZ (6w), (3w),  (3w),  (6w), WPMC (3w), RAJC (6w). Additional paratype series (RAJC), collected on June 24, 2009, include RAJ #4253 (6w) and RAJ#4255 (9w): all series have additional workers in ethanol.