Patagonomyrmex laevigatus

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) longitudinal rugae on cephalic dorsum rarely continue to posterior margin, (2) interrugae on cephalic dorsum and dorsum of promesonotum mostly smooth and shining, (3) posterior surface of petiolar node smooth and shining, (4) inferior propodeal spines triangular, height and width similar, notably shorter than superior spines, and (5) body mostly concolorous dark brownish-black to black.

Queen This caste is diagnosed by: (1) caste-specific morphology of the mesosoma related to wing-bearing and presence of ocelli on head, (2) mesoscutum and mesoscutellum smooth and shiny, (3) inferior propodeal spines triangular, much shorter than superior propodeal spines, and (4) body mostly concolorous dark brownish-black to black.

Male This caste is diagnosed by: (1) mesopleura, metapleura, pronotal sides and/or dorsum of propodeum with weak to strong rugae, (2) no hairs on ventral surface of head or those protruding from mandibles approach MOD, and (3) in profile, juncture between cephalic dorsum and posterior declivity (near posterior margin of ocelli) weakly angulate to rounded, posterior declivity weakly convex to weakly concave.

Patagonomyrmex laevigatus co-occurs with Patagonomyrmex angustus and Patagonomyrmex odoratus. Patagonomyrmex laevigatus is distinguished from Pa. angustus based on the following characters: (1) dorsum of promesonotum and posterior surface of petiolar node smooth and shining (both structures strongly granulate in Pa. angustus), and (2) inferior propodeal spines triangular, shorter than superior propodeal spines (inferior propodeal spines elongate, length similar to that of superior propodeal spines in Pa. angustus). In his key, Kusnezov (1951) separated Pa. laevigatus from Pa. odoratus based on the mostly concolorous blackish to black body (body orangish-brown with the gaster slightly darker in Pa. odoratus). Kusnezov (1949, 1951) also indicated that longitudinal rugae on the cephalic dorsum were coarser in Pa. laevigatus than in Pa. odoratus, but I could not discern this difference. He also indicated the angle between the peduncle of the petiole and the anterior surface of the petiolar node was more rounded in Pa. laevigatus, and more angulate in Pa. odoratus. This character appeared to be very subtle and inconsistent, and thus was not a useful diagnostic trait. We did not find any morphological measurements that could be used to separate Pa. laevigatus 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

 *  laevigatus. Pogonomyrmex (Ephebomyrmex) laevigatus Santschi, 1921g: 97 (w.) CHILE.
 * Kusnezov, 1949c: 301 (m., in key).
 * Combination in Ephebomyrmex: Kusnezov, 1960b: 354.
 * Combination in Pogonomyrmex: Snelling & Hunt, 1976: 75.
 * Combination in Patagonomyrmex: Johnson & Moreau, 2016: 17.

Worker
Johnson and Moreau (2016) - Lectotype (n = 12). HL 1.18 (1.11–1.24); HW 1.06 (0.97–1.13); MOD 0.28 (0.24–0.30); OMD 0.23 (0.20–0.25); SL 0.96 (0.84–0.95); PNW 0.73 (0.66–0.76); HFL 1.10 (0.99–1.16); ML 1.57 (1.32–1.53); PW 0.28 (0.25–0.31); PPW 0.42 (0.41–0.49). Indices: SI 90.57 (84.07–97.94); CI 89.83 (78.86–92.79); OI 26.42 (23.76–27.84); HFI 103.77 (97.27–113.40).

Longitudinal rugae on cephalic dorsum prominent, weakly wavy, widely-spaced, beginning on frontal lobes but rarely extending to posterior margin; posterior margin flat in full-face view. Wavy to irregular, often discontinuous rugae arc from mandibular margins to frontal lobes and traverse longitudinally above and below eyes, usually terminating before vertex; lateral rugae weaker than those on cephalic dorsum. Interrugae on cephalic dorsum smooth and shining; vertex and posterior margin of head weakly granulate-punctate, weakly shining to smooth and shining. Dorsum of clypeus with several moderately strong, subparallel, longitudinal rugae. Mandible with six teeth; mandibular dorsum strongly rugose. MOD ranging from 0.20–0.25x HL. In profile, eyes situated anterior to middle of head, OMD = 0.76–0.93x MOD. In full-face view, eyes protruding slightly beyond lateral margins of head. Antennal scapes long (SI = 84.07–97.94), surpassing vertex by less than length of second funicular segment; scapes weakly to moderately granulate-punctate, often with faint striae, weakly shining; basal flange moderately well-developed with carinate margin.

Mesosomal profile strongly convex; dorsum of promesonotum smooth and shining; longitudinal rugae on mesospleura and metapleura wavy to irregular, interrugae weakly to moderately granulate-punctate, weakly shining. Promesonotal suture absent to weakly impressed on occasional individuals. Superior propodeal spines long, narrowing to blunt tip, length rarely >0.7–0.8x the distance between their bases; inferior propodeal spines moderately well-developed, triangular, acuminate, length and width similar, distinctly shorter than superior spines. Propodeal spiracles weakly ovate to circular facing posterad. Legs weakly granulate, weakly shining to smooth and shining.

Peduncle of petiole about 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 angulate to rounded. In dorsal view, petiolar node longer than wide, sides subparallel, narrowing to rounded to bluntly angulate anterior margin. Dorsum of postpetiole convex in profile; in dorsal view, widest near posterior margin, narrowing to anterior margin, maximum width and length similar; posterior surface and sides of petiolar node and dorsum and sides of postpetiole smooth and shining; first gastral tergum smooth and shining.

Erect, short to long, copperish-brown hairs abundant on head, one to few approaching to slightly exceeding 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 moderately dense, medium to long, erect setae, longest approaching MOD; petiolar node, postpetiole, gastral terga with moderately dense, erect setae, mostly similar in length, longest notably shorter than MOD. Body mostly concolorous dark brownish-black to black.

Queen
Johnson and Moreau (2016) - (n = 2). HL 1.25–1.30; HW 1.02–1.12; MOD 0.26–0.33; OMD 0.20–0.24; SL 0.80–0.91; PNW 0.92–0.93; HFL 1.08–1.12; ML 1.56–1.63; PW 0.32–0.34; PPW 0.51–0.53. Indices: SI 71.43–89.22; CI 78.46–89.60; OI 25.49–29.46; HFI 100.00–105.88.

With caste-specific morphology of the mesosoma related to wing-bearing and presence of ocelli on head. In full-face view, head elongate (CI = 78.46–89.60), posterior margin flat. Longitudinal rugae on cephalic dorsum extending to near posterior margin, rugae fine and dense medially, density decreasing laterally and becoming weakly rugoreticulate; vertex weakly rugoreticulate. Interrugae on cephalic dorsum weakly to moderately coriarious, weakly shining. Mandible with five to six teeth, dorsal surface convex, coarsely rugose, anterior margin flat to weakly convex. Psammophore poorly-developed, consisting of short to medium-length hairs scattered across ventral surface of head.

Mesoscutum, mesoscutellum, dorsum of propodeum smooth and shining; mesopluera, metapluera, propodeal sides longitudinally rugose; interrugae weakly coriarious, weakly shining. Superior propodeal spines well-developed with blunt tips, inferior propodeal spines triangular, wider than tall, about 0.5–0.7x the length of superior spines. In profile, petiolar node asymmetrical with anterior surface shorter than posterior surface, apex subangulate. In dorsal view, postpetiole wider than long. Posterior surface of petiolar node and dorsum of postpetiole weakly coriarious, weakly shining to smooth and shining. First gastral tergum smooth and shining. Most body surfaces with moderately abundant suberect to erect, yellowish setae; gaster with fewer setae. Entire body dark brownish-black to black; legs, posterior gastral terga often with brownish infusion.

Male
(n = 4). HL 1.06–1.19; HW 0.93–1.01; MOD 0.39–0.43; OMD 0.14–0.18; SL 0.29–0.35; HFL 1.15–1.25; ML 1.62–1.73; PW 0.27–0.30; PPW 0.40–0.43. Indices: SI 30.21–37.63; CI 80.87–90.57; OI 41.58–46.24; HFI 123.66–126.88.

Type Material
Johnson and Moreau (2016) - Syntypes examined: 5 workers, 2 workers , #1077, Chile, Llanqihue Province: Cayutué (Dr. Wolffhügel leg.); Kusnezov, 1949: 301 (male, in key). MACN worker here designated Lectotype [CASENT0217258].

Etymology
Johnson and Moreau (2016) - The specific epithet, laevigatus (from Latin, laevigatus = smooth, glossy), is derived from the smooth, shiny surface over most of the body of this species.