Stenamma crypticum, 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 : 61-68

Stenamma crypticum sp. n. Worker: Figures 68, 69; Queen: Figure 70 A–D; Map: Figure 71

Stenamma mgb12 Branstetter, 2012: phylogeny.

Type material.

Holotype worker. MÉXICO, Chiapas: 2km SE Custepec, 15.72141°N, 92.93936°W, 1860m, 17 May 2008, oak-pine forest, ex sifted leaf litter (R. S. Anderson, collection RSA2008-013) [USNM, specimen CASENT0604771] Paratypes: MÉXICO, Chiapas: 3km SE Custepec, 15.71485°N, 92.93823°W ± 50m, 1700m, 17 May 2008 (LLAMA, Wa-A-02-2-50) [1dq, 1w, CAS, CASENT0623277, CASENT0623280], [1w, EAPZ, CASENT0623281], [1w, ECOSCE, CASENT0623282], [1w, FMNH, CASENT0623283], [1w, ICN, CASENT0623284], [1w, INBio, CASENT0623286], [1w, JTLC, CASENT0623536], [1w, LACM, CASENT0623288], [1w, MGBPC, CASENT0623537], [1dq, 1w, MCZ, CASENT0623278, CASENT0623289], [1w, MZSP, CASENT0623290], [1w, UCD, CASENT0623291], [1w, UNAM, CASENT0623292], [1dq, 1w, USNM, CASENT0623279, CASENT0623293], [1w, UVGC, CASENT0623294].

Worker diagnosis.

Integument dark red-brown to brown; small-sized species (see HL, ML, PrW below); basal margin of mandible sinuous, usually with a small basal depression; anterior clypeal margin undulating, with two small blunt teeth bordering midline; eye of moderate size (EL 0.07-0.11, REL 15-20), oval-shaped, with 4-5 ommatidia at greatest diameter; face mostly rugoreticulate; mesosoma often mostly sculptured, but pronotum variable, usually rugose with smooth patches on dorsum and side, but sometimes mostly rugose or mostly smooth; propodeal spines tuberculate to short (PSL 0.07-0.10, PSI 1.2-1.8); gastral pilosity usually short, dense and clearly bilayered, with a layer of suberect setae and a denser underlying layer of subdecumbent setae, but sometimes setae more uniformly subdecumbent, or suberect setae thickened; geography useful in species determination. Similar species: Stenamma connectum , Stenamma huachucanum , Stenamma ignotum , Stenamma picopicucha .

Geographic range.

Southern Mexico (Chiapas, Veracruz?) to Honduras.

Worker description.

(21 measured) HL 0.54-0.65 (0.59), HW 0.45-0.57 (0.51), FLD 0.12-0.16 (0.14), PCW 0.02-0.04 (0.03), SL 0.39-0.51 (0.42), EL 0.07-0.11 (0.08), ACL 0.39-0.48 (0.42), ML 0.62-0.79 (0.70), PrW 0.31-0.40 (0.35), PSL 0.07 -0.10 (0.09), SDL 0.05-0.06 (0.05), PL 0.22-0.29 (0.26), PH 0.13-0.18 (0.15), PW 0.11-0.16 (0.14), PPL 0.13-0.18 (0.16), PPH 0.12-0.18 (0.15), PPW 0.13-0.21 (0.16), MFL 0.40-0.54 (0.45), MTL 0.34-0.45 (0.37), CI 84-91 (87), SI 80-89 (81), REL 15-20 (16), FLI 25-29 (26), PSI 1.2-1.8 (1.6), MFI 103-117 (115), ACI1 69-72 (69), ACI2 93-103 (100).

Small-sized species; general body color dark brown to brown or orange-brown, with appendages brown or orange-brown to yellow-brown, becoming lighter toward extremities; setae golden brown; mandible with 6 teeth, inner teeth sometimes worn; basal margin of mandible sinuous, usually with a distinct basal depression, but without tooth; mandible mostly smooth and shining, with scattered piligerous punctae and some basal striae; anterior clypeal margin when viewed from anterodorsal angle undulating, usually forming 2 blunt teeth bordering midline; median lobe of clypeus with a pair of faint longitudinal carinulae that diverge anteriorly, apex of lobe with short transverse carinula; area in between median lobe and anterior clypeal margin forming a shallow concavity where mandibles insert; remaining surface of clypeus mostly smooth; posterior extension of clypeus between antennal insertions somewhat narrow (PCW 0.02-0.04), sides subparallel; frontal lobes of moderate width (FLD 0.12-0.16, FLI 25-29), not greatly obscuring torular lobes in full-face view; head subrectangular to oval-shaped (CI 84-91), posterior margin slightly depressed medially; eye somewhat small (EL 0.07-0.11, REL 15-20), oval-shaped, with 4-5 ommatidia at greatest diameter; head completely sculptured, mostly rugoreticulate, with a few longitudinal carinulae along midline; scape relatively short (SI 80-89), not reaching posterior margin of head when laid back; scape surface mostly smooth, with scattered piligerous punctae; flagellum with distinct 4-segmented antennal club, last segment noticeably bulging; pronotal sculpture variable, dorsum usually longitudinally rugose, with a small smooth patch mesad (type population), side usually rugose on upper half and smooth on lower half (type population), sometimes pronotum completely smooth, or completely rugose, with only a small smooth patch on side; dorsum of mesonotum rugulose punctate; katepisternum and side of propodeum punctate, sometimes with a few rugulae; propodeal dorsum punctate, with a few transverse carinulae; propodeal declivity mostly smooth, with a few transverse carinulae on upper half; promesonotum in profile low-domed, and roughly symmetrical; propodeal spines tuberculate to short (PSL 0.07-0.10, PSI 1.2-1.8); petiole usually somewhat short and stocky (PL/HW 0.47-0.54); petiolar node somewhat small (PH/PL 0.56-0.57), roughly symmetrical, dorsum reaching a defined apex, which points nearly vertical; postpetiole in profile variable, usually small and similar in size to petiolar node (type population), but sometimes bulging (PPH/PH 0.91-1.07); petiole and postpetiole usually mostly punctate, with anterior faces of nodes smooth, and posterior faces of nodes with a few rugulae; most of body dorsum with short standing pilosity; pilosity on gastral dorsum usually distinctly bilayered, with a layer of suberect setae, and a slightly more dense layer of decumbent setae (type population), but sometimes setae more uniformly suberect to subdecumbent and less clearly bilayered; suberect layer of setae sometimes slightly thickened; setae on scapes decumbent to appressed; setae on legs mostly subdecumbent to appressed, with longer suberect setae on femoral venters and coxae.

Queen description.

(7 measured) HL 0.59-0.67 (0.59), HW 0.52-0.61 (0.52), FLD 0.15-0.17 (0.15), PCW 0.04-0.05 (0.04), SL 0.42-0.50 (0.44), EL 0.14-0.17 (0.14), ACL 0.42-0.48 (0.44), ML 0.80-0.95 (0.80), PrW 0.46-0.55 (0.46), PSL 0.10-0.13 (0.11), SDL 0.07-0.08 (0.07), PL 0.28-0.34 (0.30), PH 0.17-0.20 (0.17), PW 0.15-0.17 (0.15), PPL 0.16-0.20 (0.18), PPH 0.17-0.22 (0.17), PPW 0.19-0.24 (0.19), MFL 0.47-0.57 (0.47), MTL 0.39-0.48 (0.41), CI 88-92 (88), SI 79-86 (84) REL 26-28 (28), FLI 26-30 (28), PSI 1.3-1.7 (1.6), MFI 102-113 (110), ACI1 68-70 (68), ACI2 90-100 (100).

Same as worker except for standard queen modifications and as follows: pronotum with transverse carinulae on humeri, becoming smooth mesad; mesoscutum mostly with longitudinal rugulae and foveolae, midline and mesolateral margin smooth; scutellum smooth along midline, and longitudinally carinulate laterad; propodeum with transverse carinulae/rugulae that wrap around surface; mesopleuron mostly smooth; lower layer of setae on gastral dorsum very dense, almost pubescent; wing venation as in Figure 70D.

Male.

Unknown.

Biology.

Stenamma crypticum is a rather common component of the leaf litter in mid- to high-elevation mesic forest habitats in Central America. It has been collected from 900-2800 m, but is most common from 1500-2500 m. Habitat types include cloud forest, mesophyll forest, oak forest, and mixed hardwood forest. Most collections come from samples of sifted leaf litter collected from the forest floor, but some specimens are also known from cookie baits. Nests have never been found, but dealate queens, as well as workers, are common in the leaf litter, suggesting that nests might be in this stratum.

Comments.

Stenamma crypticum should be distinguished easily from Stenamma ignotum and Stenamma picopicucha using the diagnostic characters given above. As noted under Stenamma connectum above, separating Stenamma crypticum from Stenamma connectum and Stenamma huachucanum is more challenging. This is because each species comprises a complex of multiple divergent populations, with no clear evidence of sympatry among distinct forms. Using morphology alone, it might be best to name a single species; however, molecular phylogenetic data strongly suggest the existence of at least three species (Branstetter unpublished data). Even though some populations/specimens may prove difficult to identify, I have chosen to delimit these species as best as possible. There are a few key morphological characters that separate the type populations of each species from one another, but when considering all populations, geography is useful.

Stenamma crypticum occurs mainly in Nuclear Central America from Chiapas, Mexico to Honduras, whereas Stenamma connectum is found north of Stenamma crypticum in Veracruz, Mexico and on the wet, Caribbean slope of Oaxaca. Complicating this picture, however, are a few specimens collected from Veracruz at 1600 m (11km N San Andrés Tuxtla). These specimens lack the broadly rounded propodeal lobes characteristic of Stenamma connectum and have a mostly smooth promesonotum. I tentatively identify these specimens as Stenamma crypticum , but I find it possible that they could actually be abberant members of Stenamma connectum , which has been collected close by at a slightly lower elevation (1400 m). The phylogenetic position of the putative Stenamma crypticum specimens has not been assessed. Stenamma huachucanum is distributed from the southwestern U.S.A. to Oaxaca, where it occurs only on the drier western side of the state. A wet forest version of Stenamma huachucanum occurs in eastern Mexico from Tamaulipas to Puebla.

Stenamma picopichuca can be separated from Stenamma crypticum using the diagnostic characters listed above, but I am somewhat uncertain about the phylogenetic placement and status of this species. Stenamma picopichucha has the basal margin of the mandible like Stenamma ignotum and the anterior clypeal margin like Stenamma crypticum . Because of several other similarities, I was originally going to include Stenamma picopicucha in Stenamma crypticum , but I later discovered that the two species occur in sympatry at Cusuco in Honduras. At this site, specimens of Stenamma crypticum clearly have a sinuous basal margin of the mandible and specimens of Stenamma picopicucha have a straight margin. The phylogenetic position of Stenamma picopicucha is yet to be tested, and it will be interesting to see if the two species are closely related.

Within the range of Stenamma crypticum there is considerable variation in size, sculpture and gastral pilosity, with some of this variation observable at single sites. At the type locality, for example, I have sampled Stenamma crypticum from 1500 m to about 2200 m elevation. Along this gradient specimens from higher elevation are larger. There is also significant variation in pronotal sculpture within the site, with some specimens having the pronotal dorsum mostly smooth (Figure 69 A–C), and others mostly rugose (Figure 69 D–F). At first I tried separating these into distinct forms, but I abandoned this scheme after finding specimens with intermediate phenotypes.

In addition to within site variation, there is considerable among population variation, with almost every population displaying some unique feature. Out of this diversity I describe a couple of variants. Variant 1 (Figure 69 G–I) occurs at several sites in Guatemala (e.g. Biotopo Quetzal, Purulhá). It is similar to the type form, but has a bulging postpetiole and longer gastral pilosity. Variant 2 (Figure 69 J–L) occurs at La Union in Guatemala, with similar-looking specimens at sites in Honduras. Compared to the type form it is smaller and has the suberect layer of gastral pilosity noticeably thickened. Until there is evidence of sympatry, I treat all of this variation as intraspecific.

Material examined.

GUATEMALA:Baja Verapaz: Biotopo Quetzal, 15.21298°N, 90.21510°W, 1750m, 7 May 2009 (LLAMA); Purulhá, Biotopin, 15.21535°N, 90.21618°W, 1700m, 26-30 Mar 2008 ( Méndez et al.); 7km E Purulhá, [ca, 15.2667°N, 90.1348°W], 1600m, 25 May 1991 (R. S. Anderson); 4.5km S Pu rulhá, [ca. 15.226°N, 90.200°W], 1630m, 21 May 1991 (R. S. Anderson); 7km S Purulhá, [ca. 15.194°N, 90.200°W], 1660m, 20 May 1991 (R. S. Anderson); 4km SSE Purulhá, 15.20522°N, 90.22198°W, 2100m, 20 Sep 2008 (M. G. Branstetter); Ranchito El Quetzal, 15.21443°N, 90.22123°W, 1750m, 20 Sep 2008 (R. S. Anderson); Salamá, Cerro Verde, 15.17446°N, 90.19353°W, 1800m, 26-30 Mar 2008 ( Méndez et al.); Salamá, Hotel Posada del Quetzal 1, 15.19710°N, 90.21169°W, 1600m, 26-30 Mar 2008 ( Méndez et al.) El Progresso: 20km N Estancia de la Virgen, 15.1141°N, 89.8833°W, 1850m, 8 Jun 1991 (R. S. Anderson); Guatemala: 1km SE La Pueblito, [ca. 14.6211°N, 90.5269°W], 1800m, 10 Jun 1991 (R. S. Anderson); nr Las Nubes, 14.53349°N, 90.35941°W, 1850m, 18 Sep 2008 (R. S. Anderson); 5.9km ESE San José Pinula, 14.53349°N, 90.35941°W, 1850m, 18 Sep 2008 (M. G. Branstetter); 7km ESE San José Pinula, 14.53915°N, 90.34933°W, 2060m, 18 Sep 2008 (M. G. Branstetter); Jalapa: Aldea Manzano, 1.8km WNW San José La Sierra, 14.50476°N, 90.25613°W, 1990m, 18 Sep 2008 (M. G. Branstetter); El Manzano, 14.50476°N, 90.25613°W, 2150m, 18 Sep 2008 (R. S. Anderson); San Marcos: La Fraternidad, 14.93604°N, 91.86778°W, 1920m, 11 Sep 2008 (M. G. Branstetter); Rd. Bojonal-Fraternidad, 14.94533°N, 91.88038°W, 1580m, 11 Sep 2008 (R. S. Anderson); 9.8km WSW San Marcos, 14.94427°N, 91.87990°W, 1600m, 11 Sep 2008 (M. G. Branstetter); Suchitepéquez: Finca Sn. Jerónimo, 14.55914°N, 91.16705°W, 1790m, 11 Dec 2010 (L. Sáenz); Volcán Atitlán, 9.5km SE Santiago Atitlán, 14.55828°N, 91.19133°W, 2000m, 10 Sep 2008 (M. G. Branstetter); 4km S Vol. Atitlán, 14.54830°N, 91.19115°W, 1625m, 15 Jun 2009 (LLAMA); 4km S Vol. Atitlán, 14.55112°N, 91.19848°W, 1750m, 15 Jun 2009 (LLAMA); Zacapa: 14km NNE Teculután, 15.1134°N, 89.6781°W, 2270m, 6 Jul 2007 (R. S. Anderson); 2km SE La Unión, 14.94701°N, 89.27594°W, 1550m, 12 May 2009 (LLAMA); HONDURAS: Comayagua: 10km E Comayagua, 14.45973°N, 87.54609°W, 2000m, 15 May 2010 (LLAMA); Cortés: PN Cusuco, 15.50739°N, 88.23373°W, 2030m, 3 Jun 2010 (LLAMA);Lempira: PN Celaque, 8.3km SW Graçias, 14.56132°N, 88.65768°W, 1860m, 30 Sep 2008 (M. G. Branstetter); PN Celaque, 8.7km SW Graçias, 14.5877°N, 88.66117°W, 2100m, 30 Sep 2008 (M. G. Branstetter); Ocotepeque: 13km E Nuevo Ocotopeque, 14.45685°N, 89.06856°W, 2200m, 25 May 2010 (LLAMA); Santa Barbara: 15km SE Santa Barbara, [ca. 14.906°N, 88.100°W], 24 Aug 1991 (S. B. Peck); MÉXICO: Chiapas: Cacahuatan, Las Nubes, [ca. 15.097°N, 92.140°W], 1770m, 1-7 Aug 1950 (Goodnights); Cerro Huitepec (Pico), 5km W San Cristobal, [ca. 16.7500°N, 92.6802°W], 2750m, 18 Sep 1991 (R. S. Anderson); Cerro de Tapalapa, 17.18786°N, 93.12308°W, 2260m, 28 May 2008 (R. S. Anderson); 5km NE Coapilla, 17.17557°N, 93.13187°W, 1990m, 25 May 2008 (LLAMA); 2km SE Custepec, 15.72099°N, 92.95050°W, 1520m, 17 May 2008 (LLAMA); 4km SE Custepec, 15.70658°N, 92.93126°W, 2125m, 20 May 2008 (LLAMA); Lagunas de Montebello, Cinco Lagos, [ca. 15.2667°N, 90.1348°W], 1660m, 23 May 1991 (R. S. Anderson); 7.4km SSW Motozintla de Mendoza, [ca. 15.367°N, 92.233°W], 2000m, 21 Sep 1992 (R. S. Anderson); Najá, 16.97417°N, 91.58592°W, 950m, 14 Jul 2007 (R. S. Anderson); 13km N Pueblo Nuevo Solistahuacán, [ca. 17.211°N, 92.964°W], 1860m, 26-27 Aug 1973 (A. F. Newton); 8.9km E Rayon, 17.20000°N, 92.91633°W, 1500m, 19 Sep 1991 (R. S. Anderson); Sierra Morena, C. Bola, 16.13464°N, 93.60077°N, 1950m, 14 May 2008 (R. S. Anderson); 17km ENE Tonalá, 16.14153°N, 93.60958°W, 1650m, 16 Jul 2007 (M. G. Branstetter); 4km N Union Juarez, Volcan Tacana, lower slopes, [ca. 15.133°N, 92.100°W], 2000m, 19 Sep 1992 (R. S. Anderson); Veracruz: 11km N San Andrés Tuxtla, 18.55°N, 96.00°W, 1600m, 23 Mar 1985 (P. S. Ward).