Pogonomyrmex mohavensis

Johnston and Overson (2009) - Nests of P. mohavensis consist of a small circular tumulus that ranges from 7.5–13 cm in diameter; the shape is evenly symmetrical and lacks the crescentic shape typical of Pogonomyrmex californicus. Nests were difficult to locate because of their low density and the small size of their tumulus; nests were most easily located by baiting foragers, then following them back to the nest. Nests were placed in various situations that included open exposed sites, under the edge of small bushes, and under dried cow dung. Pogonomyrmex mohavensis was sympatric with P. californicus at one site, and with Pogonomyrmex rugosus at the other. Workers of P. mohavensis foraged solitarily during the day, harvesting seeds and related items. Partial excavation of nests indicated that colonies reach a maximum size of about 600–700 workers. Sexual larvae and pupae were excavated from multiple nests on 24 May, 2008, indicating that reproductive sexuals begin maturing by mid-June. Mating flights are predicted to be similar to those of P. californicus, in which flights are triggered by photoperiod (not rain-triggered as in most other species of Pogonomyrmex) (Johnson 2000) and likely take place over a 2–3 week period during early summer.

Identification
Johnson and Overson (2009), Johnson et al (2013) - Worker. Pogonomyrmex mohavensis is characterized by: (1) cephalic rugae not forming circumocular whorls, but rather extending more or less directly to the vertex or converging only slightly near the vertex, (2) mandible with six teeth (a seventh sometimes occurs as a denticle between the basal and sub-basal teeth), and (3) interrugal spaces on pronotal sides smooth and shining to slightly punctate and moderately shining.

Queen. As in worker diagnosis, but with caste-specific structures related to wing-bearing, presence of small ocelli on head. Mandible with six teeth or with a seventh tooth that occurs as a denticle between the basal and sub-basal teeth. All mesosomal surfaces except for mesoscutum and mesoscutellum with prominent rugae; sculpturing absent on mesoscutum and mesoscutellum except for scattered punctures or with faint longitudinal striae. Posterior face of petiole with coarse transverse, oblique, or longitudinal rugae, dorsum of postpetiole with weaker transverse rugae. Base of scape noticeably flattened; superior and inferior lobes very well developed, wider than width of scape base.

P. mohavensis is likely to be confused only with Pogonomyrmex californicus but may be distinguished by the following characters: (1) P. mohavensis is slightly smaller (HW = 1.31–1.67) than sympatric P. californicus (HW = 1.22–1.78), (2) P. mohavensis has six mandibular teeth (a seventh sometimes occurs as a denticle between the basal and subbasal teeth), and (3) in side view, the cephalic rugae extend more or less directly to the vertex and do not converge posterior to the eyes or form circumocular whorls. In P. californicus, the mandible has seven more or less normally sized teeth and the cephalic rugae converge posterior to the eye, sometimes forming circumocular whorls. In addition, in some populations of P. californicus (including the population at the type locality of P. mohavensis) the gaster is dark brown to black. In P. mohavensis, the gaster is concolorous with the head and mesosoma, or sometimes a bit darker, but never dark brown to black.

In some specimens of both P. californicus and P. mohavensis, the cephalic rugae become weak or may even more or less disappear directly posterior to the eye, making evaluation of this sculptural character difficult, especially if magnification is low or the lighting is not good. In these cases, it appears that the number of mandibular teeth can secure separation. Even in examples of P. mohavensis with seven mandibular teeth, the extra tooth is much smaller than the flanking basal and subbasal teeth. This seventh tooth is fully developed in P. californicus and is subequal in size with the flanking teeth. Also note that substantial mandibular wear is common in older Pogonomyrmex workers, such that it is strongly recommended that at least several workers from each colony series be examined when attempting identification.

The queens of P. mohavensis and Pogonomyrmex hoelldobleri are very similar. The best characters to separate queens of these two species appear to be: (1) number of teeth (seven in P. hoelldobleri, six or with a seventh tooth that occurs as a denticle between the basal and sub-basal teeth in P. mohavensis), (2) sculpturing (posterior face of petiole and dorsum of postpetiole weakly to moderately granulate or with weak tranverse rugae in P. hoelldobleri; posterior face of petiole with coarse transverse, oblique, or longitudinal rugae, dorsum of postpetiole with weaker transverse rugae in P. mohavensis), and (3) conformation of the base of the scape (base of scape rounded, superior and inferior lobes poorly developed in P. hoelldobleri; base of scape noticeably flattened, superior and inferior lobes well developed in P. mohavensis). The queens of P. mohavensis also were significantly larger (HW = 2.01–2.08 mm) than those of P. hoelldobleri (HW = 1.44–1.79 mm). However, these queens of P. mohavensis are likely to be significantly larger than those in other parts of their range where the workers are much smaller.


 * Key to the Pogonomyrmex californicus species group

Distribution
Current records suggest that P. mohavensis is restricted to areas in and near the Mohave Desert at elevations from 245–1540 meters.

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



Biology
Queens were collected from a nest "in disturbed roadside habitat surrounded by agricultural fields." (Johnson et al. 2013)

Nomenclature

 *  mohavensis. Pogonomyrmex mohavensis Johnson, in Johnson, R.A. & Overson, 2009: 308, figs. 1A-E (w.) U.S.A. See also: Johnson, Overson and Moreau, 2013: 220 (q.m.).

Worker
Head subquadrate (CI = 97.0–104.5), broadest just posterior to eye; posterior margin flat in full-face view. Longitudinal cephalic rugae prominent, in full-face view median rugae diverging only slightly towards the posterior corners of the head. In side view, rugae posterior to eyes not converging or forming circumocular whorls, but rather extending to vertex. Vertex rugose, with rugae often becoming weak or absent on posterior corners. Cephalic interrugal spaces slightly punctate, moderately to strongly shining. Anterior margin of clypeus flat to slightly concave. Mandible with six teeth, a seventh occasionally present as a denticle or very small tooth between the basal and subbasal teeth (76% had six teeth on both mandibles, 17% had an additional denticle on one mandible, 7% had an additional denticle on both mandibles, n = 98). Mandibular dorsum coarsely striated. MOD ranging from 0.21–0.243 HL. Eyes in profile situated slightly posterior to middle of head, OMD 5 1.2–1.6 MOD. Antennal scapes relatively long (SI = 72–82), reaching to or surpassing vertex by less than the length of the basal funicular segment. Basal flange of scape flattened and very well-developed, at least partially translucent near margin. Psammophore well developed.

Mesosomal profile flattened to slightly convex. All mesosomal surfaces with prominent parallel/subparallel rugae. Dorsum of promesonotum with transverse rugae that curve obliquely to posterior on the pronotal sides, or rugae traverse obliquely from anterior to posterior. Mesopleura with transverse rugae angling posteriodorsally. Propodeum lacking spines or teeth, in side view evenly convex; rugae on propodeal dorsum transverse, posterior face of propodeum smooth and shining. Propodeal spiracles narrowly ovate. Interrugal spaces on mesosoma smooth and shining to slightly punctate and moderately shining. Legs moderately to strongly shining.

Petiolar peduncle long, ventral surface usually smooth, lacking tooth or lobe, occasionally with small angular process. In side view, petiolar node broadly but asymmetrically rounded with anterior surface notably shorter than posterior surface. Apex of node rounded, sometimes weakly angulate. In dorsal view, petiolar node longer than broad, widest anteriorly. Sides and dorsum of petiolar node moderately punctate, subshining, sculpture on dorsal surface variable: either lacking rugae, or with few transverse rugae, or up to several longitudinal rugae. 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 punctate, subshining. Gaster smooth and shining.

Erect whitish pilosity moderately abundant on head, variable in length, longest hairs not exceeding MOD. Moderately abundant suberect to semidecumbent pilosity on scape, abundant semidecumbent hairs on funicular segments. Legs with moderately abundant suberect white setae. Mesosoma, petiole, and postpetiole with moderately dense erect to flexuous white setae, often similar in length, longest reaching to or slightly exceeding MOD; gastric tergites with more abundant, slightly shorter pilosity. Entire body concolorous ferruginous orange, or with gaster sometimes slightly lighter or darker than rest of body, but never black.

Holotype (paratypes, n = 12, notation: minimum-maximum). All measurements are in millimeters. HL 1.56 (1.35–1.63); HW 1.61 (1.31–1.67); MOD 0.37 (0.30–0.37); OMD 0.46 (0.36–0.50); SL 1.14 (0.94–1.21); PNW 0.98 (0.85–1.04); HFL 1.65 (1.21–1.71); ML 1.90 (1.60–1.99); PW 0.40 (0.31–0.41); PPW 0.52 (0.45–0.56). Indices: SI 70.81 (70.06–81.75); CI 103.21 (97.04–104.55); OI 22.98 (20.95–24.82); HFI 102.48 (92.37–110.53).

Queen
Johnson et al. (2013) - (mm) (n = 2). HL 1.91–1.95; HW 2.01–2.08; MOD 0.43–0.43; OMD 0.49–0.57; SL 1.36–1.38; PNW 1.52–1.62; HFL 1.91–2.00; ML 2.60–2.70; PW 0.74–0.74; PPW 0.89–0.90. Indices: SI 66.35–67.66; CI 105.24–106.67; OI 20.67–21.39; HFI 95.02–96.15.

As in worker diagnosis, but with caste-specific structures related to wing-bearing, presence of small ocelli on head. Dorsum and sides of head with strong, widely spaced rugae, in side view rugae converging near or slightly anterior to vertex, interrugal spaces smooth and strongly shining. In full-face view, head slightly broader than long, posterior margin flat. Mandible with six teeth on one queen, the other with a seventh tooth that occurred as a denticle between the basal and sub-basal teeth, dorsal surface coarsely rugose, strongly shining. Eye not large (OI = 20.67–21.39), MOD ranging from 0.22–0.23x HL. Base of scape noticeably flattened; superior and inferior lobes very well developed, wider than width of scape base.

Mesosoma as described above, propodeum unarmed; in side view, juncture of dorsum of propodeum and propodeal declivity rounded to subangulate, sides and dorsal surface rugose, 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 weakly rounded. Postpetiole broader than long. Posterior face of petiole with coarse transverse, oblique, or longitudinal rugae, dorsum of postpetiole with weaker transverse rugae, interrugal spaces weakly to moderately punctate, sub-shining. Gastric tergites weakly coriarious to mostly smooth and shining. Most body surfaces with moderately abundant coarse suberect to erect white setae. Entire body concolorous light to dark ferruginous orange.

Type Material
Type material.—Holotype (worker) plus 123 paratypes. USA: California: Inyo Co.: Alabama Hills, 1.3 km S Junction Horseshoe Meadows & Whitney Portal Roads, 1450 m (36u 34.89N 118u 7.19W), 24 May 2008, leg. R.A. Johnson #4136. Nests were in mixed Mohavean Desert woody scrub habitat; dominant plant species included Acamptopappus sphaerocephalus, Atriplex polycarpa, Atriplex canescens, Hymenoclea salsola, Grayia spinosa, Krascheninnikovia lanata, Eriogonoum fasciculatum, Coleogyne ramosissima, Ephedra sp., Gutierrezia sp., Lycium sp., and Cuscuta sp. The holotype is deposited in the MCZ. Paratypes (n = 123 workers) all from the same locality and date as the holotype and leg. R.A. Johnson #4136 are distributed as follows: 3w CIDA, 9w CASC, 9w LACM, 15w MCZ, 9w UCDC, 12w USNM, 6w WPMC, 15w RAJC. Additional paratype series (RAJC) include RAJ #4135 (12w), #4145 (15w), and #4146 (24w); all series have additional workers in ethanol. Additional material.—USA: California: Inyo Co.: Alabama Hills at 7.5 km W Lone Pine, 1540 m, 23 May 2008 (36u 35.69N 118u 8.59W) (R.A. Johnson RAJ #4129, 15w; #4130, 6w; RAJC), Alabama Hills at 6.4 km W Lone Pine, 4950’, 14 May 2006 (R.R. Snelling #06-007, 1w; RAJC), Artists Drive, Death Valley National Monument, 800 feet, 29 Apr. 1952 (CR-537, 9w; LACM). Kern Co.: 20 mi N Bakersfield, 5 Aug. 1959 (A.C. Cole CAL-345, 16w; LACM). Nevada: Nye Co.: Hwy 374 at Rhyolite, 1090 m, 18 Apr. 2009 (R.A. Johnson, RAJ #4218, 3w; RAJC), Rock Valley at 9 mi ENE Lathrop Wells, 14 Apr. 1970 (G. & J. Wheeler NEV-777, 3w; LACM).

Etymology
The specific epithet, mohavensis, is derived from this species occurring in the Mohave Desert.