Pogonomyrmex aterrimus

Pogonomyrmex aterrimus occurs at higher elevations than its two congeners.

Identification
Johnson and Cover (2015) – Worker. Small (HW = 1.11–1.35 mm), dorsum of mesosoma rugoreticulate to vermiculate; posterior surface of petiolar node viewed from behind and above elongate, clearly longer than wide, petiolar node notably narrower than postpetiole (PW/PPW = 0.78–0.90); anterior surface of petiolar node partly to completely sculptured, dull to weakly shining; in profile, anterior surface of petiolar node forming a right to weakly obtuse angle with peduncle of petiole; dorsum of postpetiole and first gastral tergum strongly punctate, dull.

Queen. With caste-specific morphology of the mesosoma related to wing-bearing and presence of ocelli on head. Small (HW = 1.32 mm), but notably larger than conspecific workers; in dorsal view, petiolar node elongate (width/length < 0.85), relatively narrow compared to postpetiole (PW/PPW < 0.75); anterior surface of petiolar node moderately sculptured; dorsum of postpetiole and most of first gastral tergum strongly granulate-punctate, dull.

Bivariate plots demonstrate strong morphological differences between P. aterrimus and Pogonomyrmex schmitti. These differences include: (1) workers of P. aterrimus are larger (HW = 1.11–1.35 mm) compared to workers of P. schmitti (HW = 0.90–1.17 mm), (2) in dorsal view, the petiolar node of P. aterrimus is elongate, not broadly fan-shaped as in P. schmitti, (3) in dorsal view, the petiolar node width/postpetiole width is lower in P. aterrimus (PW/PPW = 0.78–0.90) compared to P. schmitti (0.87–1.03), (4) in P. aterrimus, the anterior surface of the petiolar node is partly to completely sculptured, not strongly shining, and it forms a right to weakly obtuse angle with the peduncle of the petiole, whereas in P. schmitti, the anterior surface of petiolar node is mostly smooth and shining, and it forms a noticeably obtuse angle with the peduncle of the petiole, and (5) the dorsum of the postpetiole and first gastral tergum are strongly punctate, dull in P. aterrimus, whereas these structures are smooth and shining to partly or completely punctate and weakly shining in P. schmitti.

Pogonomyrmex aterrimus is not known to be sympatric with any congener, but collections of P. schmitti proximate to those of P. aterrimus suggest that the two species may occur sympatrically.

Pogonomyrmex darlingtoni is morphologically very similar to P. aterrimus. The two forms differ mainly in degree of granulation on the interrugae of the cephalic dorsum and dorsum of the mesosoma (weakly to moderately granulate-punctate in P. aterrimus, strongly granulate-punctate in P. darlingtoni). These differences are based on very limited material, especially for P. darlingtoni, which is known only from the type series of six workers. These types were collected near the western end of the Tiburon peninsula about 170 km distant from the nearest collection of P. aterrimus. At present we believe the most conservative approach is to interpret these sculptural differences as variation between populations of a single species. Additional collecting will clarify whether or not this is correct.

Distribution based on Regional Taxon Lists
Neotropical Region: Dominican Republic, Greater Antilles, Haiti.

Biology
Johnson and Cover (2015) - Little is known about the biology or habitat affinities of P. aterrimus. The geographic range of P. aterrimus appears to be restricted to mid- to higher elevation habitats of southcentral Hispaniola. The only available habitat data (from collection labels) indicate that workers were taken in secondary montane forest edge (AL Wild #1349), tropical moist forest edge (PS Ward #11744), and a grassy field (D Lubertazzi #DL03790:001, DL03786:001, DL03785:006). These sites range in elevation from 760–1800 m (AL Wild & D Lubertazzi) to 1,515–2,120 m (Wheeler 1936). Nests in the grassy fields had their chambers under a stone.

No information is available on colony size, but it seems doubtful that colonies contain more than 200–300 workers (D. Lubertazzi, pers. comm.). One dealate queen was collected by WM Mann (MCZ), but the collection date was not given. Additional collections are needed to determine microhabitat preference and other aspects of natural history.

Nomenclature

 *  aterrimus. Pogonomyrmex (Ephebomyrmex) schmitti subsp. aterrimus Wheeler, W.M. 1936b: 197 (w.) HAITI. Combination in Ephebomyrmex: Kempf, 1972a: 106; in Pogonomyrmex: Bolton, 1995b: 339. Raised to species: Johnson & Cover, 2015: 233. Senior synonym of darlingtoni: Johnson & Cover, 2015: 233.
 * darlingtoni. Pogonomyrmex (Ephebomyrmex) schmitti subsp. darlingtoni Wheeler, W.M. 1936b: 197 (w.) HAITI. Combination in Ephebomyrmex: Kempf, 1972a: 106; in Pogonomyrmex: Bolton, 1995b: 340. Junior synonym of aterrimus: Johnson & Cover, 2015: 233.

Worker
Differing from the typical schmitti in being coal-black throughout, with only the apical portions of the mandibular blades and terminal tarsal joints brown, whereas the typical schmitti is brown-black or reddish brown, with red, mandibles, and brown legs and tips of epinotal and metasternal spines. Moreover, the whole body of aterrimus, except the posterior half of the first gastric segment and the following segments is decidedly more opaque, the thoracic rugosity coarser, the dense punctuation of the petiolar node, postpetiole and anterior half of the first gastric segment decidedly sharper. Epinotal spines longer; petiolar node narrower, less expanded anteriorly, with the anterior end more acuminate and pointed and its dorsal surface more coarsely and irregularly rugose.

Johnson and Cover (2015) - Lectotype (n = 10 + 2 paralectotypes). HL 1.29 (1.29–1.47); HW 1.11 (1.15–1.33); MOD 0.21 (0.23–0.25); OMD 0.27 (0.25–0.34); SL 0.90 (0.91–1.01); PNW 0.80 (0.81–0.93); HFL 1.23 (1.17–1.36); ML 1.50 (1.47–1.72); PW 0.39 (0.35–0.45); PPW 0.51 (0.45–0.53). Indices: SI 81.08 (69.92–84.87); CI 86.05 (88.32– 95.00); OI 18.92 (18.05–20.83); HFI 110.81 (87.97–111.57).

P. “darlingtoni”. lectotype (n = 5 paralectotypes) (see below). HL 1.29 (1.29–1.44); HW 1.21 (1.13–1.35); MOD 0.27 (0.25–0.27); OMD 0.28 (0.27–0.31); SL 0.96 (0.88–1.06); PNW 0.80 (0.79–0.86); HFL 1.32 (1.25–1.46); ML 1.59 (1.58–1.72); PW 0.37 (0.36–0.43); PPW 0.45 (0.44–0.49). Indices: SI 79.34 (77.88–79.03); CI 93.80 (87.60–94.03); OI 22.31 (19.84–22.12); HFI 109.09 (102.22–114.96).

Queen
Johnson and Cover (2015) - (n = 1). HL 1.45; HW 1.32; MOD 0.28; OMD 0.29; SL 1.06; PNW 0.96; HFL 1.36; ML 1.90; PW 0.42; PPW 0.59. Indices: SI 80.30; CI 91.03; OI 21.21; HFI 103.03.

With caste-specific morphology of the mesosoma related to wing-bearing and presence of ocelli on head. In full-face view, head longer than broad (CI = 91.03), posterior margin flat. Longitudinal rugae on cephalic dorsum prominent, wavy to irregular, area posterolateral to frontal carinae and posterior margin weakly to moderately rugoreticulate; interrugae strongly granulate, dull. Mandible with six teeth, dorsal surface coarsely rugose. Eye relatively small, situated anterior to middle of head. Base of antennal scape weakly to moderately granulate, distal portion strongly granulate, dull. Psammophore poorly-developed, consisting of short hairs scattered across ventral side of head.

All mesosomal surfaces with subparallel, weakly irregular rugae to rugoreticulate. Pronotal collar rugoreticulate, mesoscutellum and scutellum with irregular longitudinal rugae. Dorsum of propodeum with wavy to irregular transverse rugae, sides rugoreticulate. Propodeum with long, well-developed superior and inferior spines, inferior spines about 0.6–0.7x the length of superior spines. In profile, petiolar node asymmetrical with anterior surface notably shorter than posterior surface, apex of node subangulate. In dorsal view, petiolar node longer than wide (width/length < 0.85), widest near middle, tapering to a rounded to subangulate anterior margin. Anterior surface of petiolar node moderately sculptured; sides and posterior surface rugoreticulate and “lumpy” in appearance, interrugae moderately granulate. In dorsal view, postpetiole widest near posterior margin, tapering to anterior margin, maximum width about equal to length, relatively narrow compared to petiolar node (PW/PPW < 0.75), all surfaces strongly granulate, dull. Anterior one-half of first gastral tergum strongly granulate, dull, posterior portion moderately coriarious, weakly shining. Moderately abundant yellowish-brown to brownish hairs on entire body, longest hairs on head and mesosoma approach to slightly exceed MOD. Entire body concolorous dark reddish-brown.

Type Material
Described from three specimens taken by Dr. Darlington between La Visite and Kenscoff, Haiti, at an altitude of 5000-7000 ft.



Etymology
Johnson and Cover (2015) - The specific epithet, aterrimus (Latin, ater = black; -rimus = superlative suffix), was derived from the deep coal black coloration of this species, which Wheeler mentioned in his description.