Pogonomyrmex aterrimus Wheeler 1936

Johnson, Robert A. & Cover, Stefan P., 2015, A taxonomic revision of the seed-harvester ant genus Pogonomyrmex (Hymenoptera: Formicidae) on Hispaniola, Zootaxa 3972 (2), pp. 231-249 : 233-234

Pogonomyrmex aterrimus Wheeler 1936 NEW STATUS

( Figures 1–3 )

Pogonomyrmex (Ephebomyrmex) schmitti aterrimus Wheeler, 1936: 197 (worker). Syntypes examined: 3 workers [MCZ]; HAITI, between La Visite and Kenscoff, 5,000–7,000 feet (Dr. Darlington leg., autumn 1934) (MCZ worker here designated LECTOTYPE [CASENT0217240]).

Ephebomyrmex schmitti aterrimus (Wheeler) ; Kempf, 1972: 106. First combination in Ephebomyrmex .

Pogonomyrmex schmitti aterrimus Wheeler ; Bolton, 1995: 339. Revived combination in Pogonomyrmex .

Pogonomyrmex (Ephebomyrmex) schmitti darlingtoni Wheeler, 1936: 197 (worker). Syntypes examined: 6 workers [MCZ]; HAITI, northeastern foothills of Massif de la Hotte, 2,000–4,000 feet (Dr. Darlington leg., 10 October, 1934) (MCZ worker here designated LECTOTYPE [CASENT0217241]). NEW SYNONOMY

Ephebomyrmex schmitti darlingtoni (Wheeler) ; Kempf, 1972: 106. First combination in Ephebomyrmex .

Pogonomyrmex schmitti darlingtoni Wheeler ; Bolton, 1995: 340. Revived combination in Pogonomyrmex .

Worker. Diagnosis. 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 ( Figure 1 ).

Measurements. 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).

Measurements for 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) ( Figure 2 ).

Queen (dealate). Diagnosis. 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 ( Figure 3 ).

Measurements (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.

Description. 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 ( Figure 2 ).

Male. Unknown.

Additional material examined. DOMINICAN REPUBLIC: La Vega: Constanza, 3,000–4,000’, Aug 1938 (PJ Darlington; MCZ). Pedernales: Parque Nacional Sierra Bahoruco, 760 m, Sept 2, 2001 (AL Wild; RAJC); Sierra Bahoruco, 1790 m & 1800 m, Mar 29, 2014 (D Lubertazzi; MCZ, RAJC); 16 km ENE Pedernales, 800 m, Sept 10, 1992 (PS Ward; MCZ, UCDC). HAITI: Quest: Furcy, no date (WM Mann; MCZ, USNM), Petionville, no date (WM Mann; USNM).

Etymology. 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.

Discussion and biology. Genetic data are not available for P. aterrimus , but bivariate plots demonstrate strong morphological differences between P. at err imus and P. schmitti ( Figure 4 ). 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. Workers of these two species are easily distinguished using characters described above.

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 ( Figure 5 A), 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. Because this is a judgement call, we provide lectotype photographs and morphometric data for both taxa ( Figures 1 , 2 , 4 ).

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 ( Figure 5 A). 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.

Figures

FIGURE 1. Photograph of Pogonomyrmex aterrimus Wheeler lectotype worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT 0217240). Photographs by Erin Prado from www. antweb. org.

FIGURE 2. Photograph of Pogonomyrmex “ darlingtoni ” Wheeler lectotype worker: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT 0217241). Photographs by Erin Prado from www. antweb. org.

FIGURE 3. Photograph of Pogonomyrmex aterrimus Wheeler dealate queen: (A) frontal view of head, (B) lateral view of body, and (C) dorsal view of body (CASENT 0217248). Photographs by Erin Prado from www. antweb. org.

FIGURE 4. Bivariate plots for workers and queens of Pogonomyrmex aterrimus, Pogonomyrmex “ darlingtoni ”, and Pogonomyrmex schmitti: (A) head width versus head length, (B) head width versus maximum length of hind femur, and (C) head width versus the ratio of maximal petiolar node width / maximal postpetiole width. Sample size for each caste is in parentheses.

FIGURE 5. Geographic distribution for (A) Pogonomyrmex aterrimus (▲), P. “ darlingtoni ” (■), and P. saucius (●), and (B) P. schmitti (●). The bold line down the left-center of the map is the border between Haiti and the Dominican Republic; lighter lines are the first administrative divisions in each country. Both maps are drawn on the same geographic area so that distribution patterns are directly comparable.