Patagonomyrmex angustus

Observations made by Kusnezov (1949, 1953, 1960) form the bulk of what is known about the biology of ants in this genus. Most of his observations were for Patagonomyrmex odoratus, but the biology of these three species appears similar, and thus all three species are discussed together. Nests are variable, ranging from an entrance lacking a tumulus to one that is 10–12 cm in diameter. Typically, nests are located in open areas or under stones or other objects. Workers of all three species are diurnal, slow-moving, solitary foragers that are timid and non-aggressive. Little information is available on food items collected, though Kusnezov (1960) indicated that they were granivores. Colonies of P. odoratus probably contain fewer than 300–400 workers (Kusnezov, 1949); colony size for Patagonomyrmex angustus and Patagonomyrmex laevigatus appears to be similar (Kusnezov, 1949; 1960; pers. obs.).

Identification
Johnson and Moreau (2016) - Worker Uniquely characterized by the following combination of features: (1) strongly granulate-punctate interrugae on cephalic dorsum and dorsum of mesosoma, (2) posterior surface of petiolar node and dorsum of postpetiole moderately to strongly granulate-punctate, weakly shining to dull, (3) rugae on cephalic dorsum continue to posterior margin, (4) inferior propodeal spines long, length similar to that of superior spines, and (5) body concolorous dark brownish-black to black, usually with dark brown legs

Queen This caste is diagnosed by: (1) caste-specific morphology of the mesosoma related to wingbearing and presence of ocelli on head, (2) mesoscutum and mesoscutellum with weak to moderately strong longitudinal rugae, interrugae weakly to strongly granulate-punctate, (3) inferior propodeal spines elongate, length similar to that of superior propodeal spines, and (4) body concolorous brownish-black to black.

Male This caste is diagnosed by: (1) mesopleura, metapleura, pronotal sides, and dorsum of propodeum strongly granulate, dull, with a beaded appearance, (2) at least several hairs on ventral surface of head approach or exceed MOD, and (3) scape length sometimes >0.6 mm, SI > 70.0.

Patagonomyrmex angustus co-occurs with both Patagonomyrmex laevigatus and Patagonomyrmex odoratus. It is distinguished from the latter two species based on the following characters: (1) dorsum of promesonotum and posterior surface of petiolar node strongly granulate-punctate, weakly shining (dorsum of promesonotum and posterior surface of petiolar node smooth and shining in Pa. laevigatus and Pa. odoratus), and (2) inferior propodeal spines elongate, length similar to that of superior propodeal spines (the inferior propodeal spines are triangular and notably shorter than superior propodeal spines in Pa. laevigatus and Pa. odoratus). We did not find any morphological measurements that could be used to separate Pa. angustus from its two congeners.

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Chile.

Biology
Alate queens and males are known for all three species; collection dates for sexuals range from October 9 to May 27 for Patagonomyrmex angustus (October 9–22 in Chile; November 16 to May 27 in Argentina), January 25 to February 17 for Patagonomyrmex laevigatus, and January 15 to February 18 for Patagonomyrmex odoratus (Kusnezov, 1949; R.A. Johnson, unpub. data). Number of sexuals in nests ranged from 1–18 alate queens and 1–7 males in Pa. angustus, 4–5 alate queens and 5– 19 males in Pa. laevigatus, and 1–54 alate queens and 1–19 males in Pa. odoratus (Kusnezov, 1949). Mating flights are unknown for all three species, but the above dates suggest that flights occur during the austral summer, probably from late January through March or later. The trigger for mating flights is unknown. Nest excavations indicate that colonies of all three species typically contain 1–2 reproductive (dealate) queens (Pa. odoratus: 1 queen [n = 1], 2 queens [1]; Pa. laevigatus: 1 queen [1]; Pa. angustus: 1 queen [3], 2 queens [1]) (see Kusnezov, 1949; R.A. Johnson, unpub. data).

All three species of Patagonomyrmex are restricted to cool, relatively humid, short growing-season climates in southern Argentina and southern to southcentral Chile, typically in habitats dominated by Nothofagus or Austrocedrus (=Libocedrus in Kusnezov, 1949). Patagonomyrmex laevigatus has the most restrictive distribution as it is only known from shady areas in well-developed mesophilic coihue (Nothofagus dombeyi) forests, i.e., it is absent from arid and semi-arid habitats including Austrocedrus forests (Kusnezov, 1949). Patagonomyrmex angustus and Pa. odoratus also have relatively localized distributions in Argentina, but both species have broader distributions in Chile; Pa. odoratus occurs north to near Santiago (Solervicens et al., 1991; specimens not examined), and Pa. angustus is common to as far north as the Valparaíso Region. Both Pa. odoratus and Pa. angustus occur in several biogeographic zones-bioclimatic regions in Chile, whereas Pa. laevigatus has a very restricted distribution. Using the ecoregions defined by Olson et al. (2001), Pa. angustus occurs in the Validivian Temperate Forest and Chilean Matorral ecoregions, with one record from the western edge of the Patagonian Steppe; both Pa. laevigatus and Pa. odoratus are restricted to the Valdivian Temperate Forest ecoregion.

All three species of Patagonomyrmex can be sympatric, but each species more typically occurs in different microhabitats. Patagonomyrmex odoratus sometimes co-occurs with Pa. laevigatus in shaded Nothofagus forests, but it is more common in exposed, slightly drier microsites such as open areas with low densities of Chilean cedar (Austrocedrus chilensis) (Kusnezov, 1949). Patagonomyrmex angustus occurs over the widest range of microhabitats, including the Araucaria, Nothofagus, and Austrocedrus zones, largely in more exposed, drier microhabitats than those used by both Pa. laevigatus and Pa. odoratus. Patagonomyrmex laevigatus occurs at elevations from ~220->1000 m in Chile and 560–950 m in Argentina, Pa. odoratus ranges from 540–1700 m in Argentina and from ~1000–1940 m in Chile, and Pa. angustus ranges from 390–1005 m in Argentina, and from 0– 2000 m in Chile.

Nomenclature

 *  angustus. Pogonomyrmex angustus Mayr, 1870b: 970 (w.) CHILE. Mayr, 1887: 612 (q.m.).
 * Combination in P. (Ephebomyrmex): Emery, 1921f: 48.
 * Combination in Ephebomyrmex: Kusnezov, 1960b: 353.
 * Combination in Pogonomyrmex: Snelling & Hunt, 1976: 72.
 * Combination in Patagonomyrmex: Johnson & Moreau, 2016: 12.
 * See also: Gallardo, 1932b: 103.

Worker
Johnson and Moreau (2016) - Lectotype (n = 15). HL 1.25 (0.97–1.32); HW 1.12 (0.81–1.16); MOD 0.27 (0.21–0.29); OMD 0.27 (0.18–0.26); SL 0.93 (0.78–1.00); PNW 0.79 (0.59–0.82); HFL 1.21 (0.89–1.25); ML 1.59 (1.21–1.58); PW 0.31 (0.23–0.34); PPW 0.44 (0.36–0.51). Indices: SI 83.01 (83.04–104.94); CI 89.60 (80.58–91.74); OI 24.11 (21.55–29.63); HFI 108.04 (103.60–118.52).

Longitudinal rugae on cephalic dorsum coarse, weakly wavy, running from frontal lobes to posterior margin; posterior margin flat in full-face view. Rugae on lateral surfaces more irregular, usually weaker than those on cephalic dorsum. Interrugae on cephalic dorsum strongly granulate-punctate, dull; vertex rugose. Dorsum of clypeus with several moderately coarse, subparallel, longitudinal rugae. Mandible with six teeth; mandibular dorsum strongly rugose. MOD ranging from 0.19–0.24x HL. In profile, eyes situated anterior to middle of head, OMD = 0.73–1.05x MOD. In full-face view, eyes protruding slightly beyond lateral margins of head. Antennal scapes long (SI = 83.01–104.94), reaching vertex; scapes moderately to strongly granulate-punctate, often with faint striae, dull; basal flange moderately well-developed with carinate margin.

Mesosomal profile weakly convex; dorsum of promesonotum with moderately coarse, irregular rugae; longitudinal rugae on mesospleura and metapleura wavy to irregular. Interrugae on promesonotum strongly granulate-punctate, dull; promesonotal suture usually faintly to weakly impressed. Superior propodeal spines long, acuminate, length rarely >0.7–0.8x the distance between their bases; inferior propodeal spines well-developed, longer than wide, acuminate, length similar to that of superior spines. Propodeal spiracles weakly ovate to circular facing posterad. Legs smooth and shining to weakly granulate, weakly shining.

Peduncle of petiole about 0.7x as long as petiolar node, anteroventral margin of peduncle of petiole with a small, acuminate spine. In profile, posterior surface of petiolar node weakly convex; petiolar node asymmetrical with anterior surface shorter than posterior surface, apex bluntly subangulate to rounded. In dorsal view, petiolar node longer than wide, sides subparallel, narrowing to a rounded to subangulate anterior margin; all surfaces of petiolar node strongly granulate-punctate, dull, occasionally with few weak rugae. Dorsum of postpetiole convex in profile; in dorsal view, widest near posterior margin, narrowing to anterior margin, maximum width and length similar; dorsum and sides moderately granulate-punctate, weakly shining. First gastral tergum smooth and shining.

Erect to suberect, medium-length, white to cream colored hairs moderately abundant on head, few hairs >0.5x MOD. Moderately abundant subdecumbent to decumbent hairs on antennal scapes; abundant decumbent to appressed hairs on funicular segments. Legs with moderately abundant subdecumbent to decumbent setae. Mesosoma with moderate number of medium-length erect to suberect setae, but few present on propodeum, longest hairs usually about 0.7–0.8x MOD; petiolar node, postpetiole, gastral terga with sparse medium-length setae, longest notably shorter than MOD. Body mostly concolorous dark brownish-black to black; antennae, legs dark brown.

Queen
Johnson and Moreau (2016) - (n = 11). HL 1.10–1.39; HW 0.99–1.22; MOD 0.26–0.31; OMD 0.18–0.30; SL 0.82–1.03; PNW 0.71–0.97; HFL 1.06–1.28; ML 1.57–1.87; PW 0.33–0.38; PPW 0.46–0.59. Indices: SI 79.66–87.27; CI 82.58–94.40; OI 22.13–28.44; HFI 99.15–110.09.

Male
Johnson and Moreau (2016) - (n = 6). HL 1.03–1.19; HW 0.88–1.01; MOD 0.35–0.42; OMD 0.11–0.22; SL 0.28–0.78; HFL 1.11–1.23; ML 1.54–1.71; PW 0.26–0.30; PPW 0.42–0.49. Indices: SI 31.82–80.41; CI 84.62–92.59; OI 36.08–43.18; HFI 117.00–126.14.

Type Material
Johnson and Moreau (2016) - Syntypes examined: 2 workers, 1 worker , Chile, Valdivia (Edm. Reitter); NHMW worker here designated Lectotype [CASENT0173374].

Mayr (1870) described the worker of Pa. angustus in a key with no additional information, and he later described the queen and male (Mayr, 1887) listing the type locality as “Valdivia in Chile”. As noted by Kusnezov (1949), this vague location does not indicate if the type locality was in the city or province of Valdivia.

Etymology
Johnson and Moreau (2016) - The name of this species, angustus (from Latin, angustus = narrow, small), is derived from the narrow body, as discussed in the description by Mayr.