Stenamma ignotum, Branstetter, Michael G., 2013

Branstetter, Michael G., 2013, Revision of the Middle American clade of the ant genus Stenamma Westwood (Hymenoptera, Formicidae, Myrmicinae), ZooKeys 295, pp. 1-277 : 105-109

Stenamma ignotum sp. n. Worker: Figures 96, 97; Queen: Figure 98 A–D; Male: Figure 98 E–G; Map: Figure 99

Stenamma mgb10 Branstetter, 2012: phylogeny.

Type material.

Holotype worker. MÉXICO: Chiapas, 2km SE Custepec, 15.72102°N, 92.95013°W ± 50m, 1520m, 17 May 2008, mesophyll forest, ex sifted leaf litter (LLAMA, collection Wa-A-02-1-09) [USNM, specimen CASENT0603762]. Paratypes: same data as holotype [1w, CAS, CASENT0623311], [1w, EAPZ, CASENT0623312]; same data but 3km ESE Custepec, 15.71660°N, 92.93715°W ± 50m, 1700m, 18 Jul 2007 (J. Longino, JTL6073) [1w, ECOSCE, CASENT0620158], [1w, FMNH, CASENT0620159], [1w, ICN, CASENT0620160], [1w, INBio, CASENT0620161], [1w, LACM, CASENT0620162], [1w, MCZ, CASENT0622764], [1q, 1w, USNM, CASENT0600182, CASENT0622765]; 15.71508°N, 92.93822°W ± 50m, 1700m, 17 May 2008 (LLAMA, Wa-A-02-2-45) [1w, MZSP, CASENT0623320], [1w, UCD, CASENT0623321], [1w, UNAM, CASENT0623322], [1w, UVGC, CASENT0623324], [1w, JTLC, CASENT0623323], [2w, MGBPC, CASENT0623326, CASENT0623325].

Worker diagnosis.

Integument mostly dark brown to brown; small-sized species (see HL, ML, PrW below); basal margin of mandible straight, never with a basal notch or depression; anterior clypeal margin with a shallow median emargination (best viewed from an anterodorsal angle); face completely sculptured, mostly rugoreticulate; mesosoma mostly sculptured, dorsum of promesonotum with dense longitudinal rugae; eye of moderate size (EL 0.10-0.12, REL 18-21), oval-shaped, with 5-7 ommatidia at greatest diameter; gastral pilosity relatively long, sparse, and mostly suberect, sometimes with a few underlying decumbent setae; petiole in profile appearing somewhat elongate; petiolar node reaching a distinct apex, which points vertically; propodeal spines tuberculate to short (PSL 0.07-0.12, PSI 1.2-2.1); frontal lobes of moderate width (FLD 0.14-0.16, FLI 24-27), not greatly obscuring torular lobes in full-face view. Similar species: Stenamma crypticum , Stenamma nonotch , Stenamma picopicucha .

Geographic range.

Southern Mexico to Guatemala.

Worker description.

(18 measured) HL 0.59-0.68 (0.64), HW 0.53-0.61 (0.55), FLD 0.14-0.16 (0.14), PCW 0.02-0.03 (0.02), SL 0.47-0.55 (0.50), EL 0.10-0.12 (0.10), ACL 0.45-0.52 (0.49), ML 074-0.86 (0.74), PrW 0.36-0.43 (0.37), PSL 0.07-0.12 (0.07), SDL 0.05-0.07 (0.05), PL 0.25-0.32 (0.27), PH 0.15-0.18 (0.15), PW 0.11-0.16 (0.12), PPL 0.14-0.18 (0.15), PPH 0.13-0.17 (0.13), PPW 0.15-0.19 (0.15), MFL 0.52-0.62 (0.54), MTL 0.42-0.50 (0.45), CI 87-92 (87), SI 85-96 (89), REL 18-21 (18), FLI 24-27 (26), PSI 1.2-2.1 (1.6), MFI 96-104 (103), ACI1 66-70 (67), ACI2 92-100 (98).

Small-sized species; general body color mostly dark brown to brown, with appendages brown to orange-brown, becoming lighter toward extremities; setae golden brown; mandible with 5-6 teeth, consisting of 3 distinct apical teeth, a basal tooth, and 1-2 smaller inner teeth/denticles, which are often worn and indistinct; basal margin of mandible straight, without basal notch or depression; mandible mostly smooth and shiny, with scattered piligerous punctae, and some striations around base and along lateral surface; anterior clypeal margin with a shallow median emargination (best viewed from anterodorsal angle); median lobe of clypeus with a pair of faint longitudinal carinulae that diverge toward anterior margin, apex of lobe with a short transverse carinula, remainder of clypeus mostly smooth; posterior extension of clypeus between antennal insertions of moderate width (PCW 0.02-0.03), sides subparallel to slightly hour-glass-shaped; frontal lobes of moderate width (FLD 0.14-0.16, FLI 24-27), not greatly obscuring torular lobes in full-face view; head roughly oval-shaped (CI 87-92), with posterior margin slightly depressed medially; eye of moderate size (EL 0.10-0.12, REL 18-21), oval-shaped, with 5-7 ommatidia at greatest diameter; face mostly rugoreticulate, with some longitudinal rugae along midline; scape of moderate length (SI 85-96), almost reaching posterior margin when laid back; scape surface smooth and shiny, with scattered piligerous punctae; flagellum with distinct 4-segmented antennal club; mesosoma almost completely sculptured except for a small patch of smooth cuticle on side of pronotum; dorsum of pronotum densely rugose (longitudinal orientation), transitioning to rugoreticulae on mesonotum; upper half of side of mesonotum rugose; mesopleuron mostly punctate, with some rugulae; side of propodeum rugulose-punctate; dorsum and declivity of propodeum with transverse carinulae; promesonotum in profile low-domed, slightly asymmetrical with apex shifted anterior of midpoint; metanotal groove of moderate width and depth; propodeal spines tuberculate to short (PSL 0.07-0.12, PSI 1.2-2.1); petiole appearing of moderate length to slightly elongate (PL/HW 0.47-0.54); petiolar node in profile of moderate height (PH/PL 0.55-0.66), and roughly symmetrical, dorsum pointing vertically to slightly posteriad, and usually reaching a well-defined apex; postpetiole in profile slightly asymmetrical, with anterior face longer and more sloping than posterior face, overal size similar to petiolar node (PPH/PH 0.85-0.98); anterior faces of petiolar and postpetiolar nodes mostly smooth and shiny, remaining surfaces faintly punctate; gaster smooth and shiny, with scattered piligerous punctae; most of body dorsum with short to long standing pilosity; setae on gastral dorsum relatively sparse, mostly long and suberect, with a few shorter decumbent setae underneath; setae on scape and legs decumbent to appressed, with some longer suberect setae on femoral venters and coxae.

Queen description.

(5 measured) HL 0.66-0.74 (0.66), HW 0.61-0.67 (0.61), FLD 0.15-0.18 (0.15), PCW 0.02-0.03 (0.03), SL 0.52-0.58 (0.52), EL 0.17-0.20 (0.17), ACL 0.49-0.55 (0.49), ML 0.94-1.09 (0.94), PrW 0.54-0.63 (0.54), PSL 0.13-0.17 (0.13), SDL 0.09-0.10 (0.10), PL 0.37-0.40 (0.37), PH 0.19-0.22 (0.19), PW 0.16-0.19 (0.16), PPL 0.16-0.22 (0.16), PPH 0.18-0.23 (0.18), PPW 0.20-0.24 (0.20), MFL 0.59-0.70 (0.59), MTL 0.50-0.58 (0.50), CI 90-93 (92), SI 85-91 (85), REL 28-30 (28), FLI 25-27 (25), PSI 1.4-1.7 (1.4), MFI 95-103 (1.03), ACI1 64-68 (67), ACI2 94-96 (96).

Same as worker except for standard queen modifications and as follows: pronotum with transverse rugae/carinulae; mesoscutum densely longitudinally carinulae; scutellum rugose to rugoreticulate; propodeum with transverse carinulae that wrap around entire surface; mesopleuron mostly smooth; gastral pilosity denser, especially lower decumbent layer; wing as in Figure 98D.

Male.

See Figure 98 E–G.

Biology.

Stenamma ignotum is found in a diversity of wet forest habitats (e.g. cloud forest, mesophyll forest, wet oak forest) from 500 m to 2070 m elevation, but is most common above 1,000 m. Most collections are from sifted leaf litter taken from the forest floor, but it is also known from cookie baits and by general searching. A couple of nests have been found: one underneath a rock, and the other under epiphytes on the ground, both in montane wet forest. A single stray worker has been collected from a mud bank.

Comments.

This species is very similar to Stenamma crypticum , Stenamma nonotch , and Stenamma picopicucha , but should always be separable by its having the basal margin of the mandible straight and the anterior clypeal margin with a distinct median emargination. Some specimens of Stenamma nonotch have a nearly imperceptible notch in the anterior clypeal margin, but this is always very insignificant compared to the emargination present in Stenamma ignotum . Sculpture on the pronotal dorsum can be compared to confirm species status, with Stenamma ignotum always having distinct longitudinal carinulae and Stenamma nonotch having rugoreticulae or very irregular rugae. As described in the comments section of Stenamma crypticum and Stenamma picopicucha , the latter species is intermediate between Stenamma crypticum and Stenamma ignotum and it is unclear to which it is most closely related. There is a significant gap in distribution between Stenamma ignotum and Stenamma picopicucha , so I highly doubt that they are conspecific, but this has yet to be tested by including Stenamma picopicucha in a molecular phylogeny.

There is some variation in size and sculpture among populations of Stenamma ignotum , but the differences are minute. The only exception is a distinct variant (Figure 97) known from a single specimen from Guatemala (7.3km E Purulhá). This specimen has very long propodeal spines, and the dorsum of the petiolar node in profile reaches a rather sharp apex, which points distinctly posteriad. Until more specimens are found, I treat this variation as intraspecific. I have noticed that many species become more aberrant in the area near Purulhá, possibly because the area is very wet and cold.

I have sampled a number of populations of Stenamma ignotum for molecular phylogenetic analysis (Branstetter unpublished data). The data indicate that the species is monophyletic and is sister to Stenamma stictosomum . I have not been able to find any morphological characters to adequately diagnose this clade.

Material examined.

GUATEMALA: Baja Verapaz: 7.3km E Purulhá, 15.267°N, 90.132°W, 1700m, 19 May 1991 (R. S. Anderson); Quetzaltenango: Km 240 road from coast-Zunil, Finca Santa Maria, 14.71686°N, 91.53481°W, 1500m, 13 Sep 2008 (R. S. Anderson); 1.7km SW Santa Maria, 14.7169°N, 91.5348°W, 1515m, 13 Sep 2008 (L. Sáenz); San Marcos: Rd. Bojonal-Fraternidad, 14.94533°N, 91.88038°W, 1580m, 11 Sep 2008 (R. S. Anderson); 9.8km WSW San Marcos, 14.9443°N, 91.8799°W, 1600m, 11 Sep 2008 (M. G. Branstetter); Suchitepéquez: 4km S Vol. Atitlán, 14.54804°N, 91.19191°W, 1575m, 16 Jun 2009 (LLAMA); 4km S Vol. Atitlán, 14.54391°N, 91.19434°W, 1435m, 17 Jun 2009 (LLAMA); 5.5km S Vol. Atitlán, 14.52857°N, 91.19569°W, 1070m, 18 Jun 2009 (J. Longino); MÉXICO:Chiapas: 5.9km E Bochil, [ca. 16.9947°N, 92.8357°W], 1300m, 15 Sep 1992 (R. S. Anderson); 5km NE Coapilla, 17.17602°N, 93.13293°W, 1990m, 26 May 2008 (LLAMA); 5km NNW Coapilla, 17. 18355°N, 93.15222°W, 1915m, 26 May 2008 (LLAMA); 5.8km NE Coapilla, 17.17453°N, 93.13152°W, 2030m, 12 Jul 2007 (R. S. Anderson); Custepec, 15.71264°N, 92.94037°W, 1660m, 18 May 2008 (J. Longino); 2km SE Custepec, 15.72099°N, 92.95045°W, 1520m, 17 May 2008 (LLAMA); 2km SE Custepec, 15.7212°N, 92.9391°W, 1830m, 18 May 2008 (R. S. Anderson); 3km SE Custepec, 15.71512°N, 92.93797°W, 1700m, 17 May 2008 (LLAMA); Lagos de Montebello, Cinco Lagos, [ca. 16.1167°N, 91.6833°W], 1500m, 22 Sep 1992 (R. S. Anderson); 2.1km NW Pueblo Nuevo Solistahuacan, Yerbabuena Preserve, [ca. 17.183°N, 92.900°W], 2070m, 23 Sep 1992 (R. S. Anderson); 4.8km N Pueblo Nuevo Solistahuacán, [ca. 17.185°N, 92.905°W], 1860m, 26-27 Aug 1973 (A. F. Newton); 5km E Rayón, 17.217°N, 92.967°W, 1700m, 23 Dec 1991 (P. S. Ward); 8.9km E Rayon, 17.20000°N, 92.91633°W, 1500m, 19 Sep 1991 (R. S. Anderson); Sierra Morena, 16.15292°N, 93.60051°W, 1330m, 12 May 2008 (LLAMA); 4km N Union Juarez, Volcan Tacana, lower slopes, [ca. 15.133°N, 92.100°W], 1800m, 18 Sep 1992 (R. S. Anderson); Oaxaca: Mirador Grande, 17.89844°N, 96.36253°W, 990m, 14 Aug 2009 (M. G. Branstetter); 10.8km SW Valle Nacional, 17.68102°N, 96.33026°W, 1120m, 13 Aug 2009 (M. G. Branstetter); 13.2km SW Valle Nacional, 17.65934°N, 96.33426°W, 1360m, 11 Aug 2009 (M. G. Branstetter); 20.5km SW Valle Nacional, 17.60560°N, 96.38298°W, 1770m, 12 Aug 2009 (M. G. Branstetter); 20.6km SW Valle Nacional, 17.60404°N, 96.37786°W, 1733m, 13 Aug 2009 (M. G. Branstetter); Veracruz: Los Tuxtlas, 10km NNW Sontecomapan, 18.583°N, 95.083°W, 500m, 21 Mar 1985 (P. S. Ward); 11km N San Andrés Tuxtla, 18.550°N, 95.200°W, 1400m, 23 Mar 1985 (P. S. Ward).