Stenamma ochrocnemis, 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 : 169-175

Stenamma ochrocnemis sp. n. Worker: Figures 134, 135; Queen: Figure 136; Map: Figure 137

Stenamma mgb02 [variant 2 below] Branstetter, 2012: phylogeny.

Type material.

Holotype worker. HONDURAS, Comayagua: 10km ENE Comayagua, 14.45982°N, 87.54564°W ± 20m, 2000m, 15 May 2010, cloud forest, ex sifted leaf litter (LLAMA, collection Wa-C-03-1-11) [USNM, specimen CASENT0621468]. Paratypes: same data as holotype but 14.45980°N, 87.54573°W ± 20m, 2000m, 15 May 2010 (LLAMA, Wa-C-03-1-09) [1dq, 1w, USNM, CASENT0621449, CASENT0621450], [1w, CAS, CASENT0621451]; 14.45994°N, 87.54523°W ± 20m, 2000m, 15 May 2010 (LLAMA, Wa-C-03-1-21) [1dq, 1w, EAPZ, CASENT0621501, CASENT0621502], [1w, ECOSCE, CASENT0621503], [1w, FMNH, CASENT0623437], [1w, ICN, CASENT0623438], [1w, INBio, CASENT0623439], [1w, JTLC, CASENT0623440], [1w, LACM, CASENT0623442], [1dq, 1w, MGBPC, CASENT0623441 CASENT0623443]; 14.46032°N, 87.54512 ± 20m, 2000m, 15 May 2010 (LLAMA, Wa-C-03-1-30) [1w, MCZ, CASENT0623444], [1w, MZSP, CASENT0623445], [1w, UCD, CASENT0623446], [1w, UNAM, CASENT0623447], [1w, UVGC, CASENT0623448].

Worker diagnosis.

Integument mostly dark red-brown to orange-brown, with appendages a distinctly lighter, uniform yellow-brown; small- to medium-sized species (see HL, ML, PrW below); anterior clypeal margin undulating, usually with 4 sharp to blunt teeth, outer teeth often larger and sharper; basal margin of mandible usually sinuous, with a shallow to very deep basal depression, but without a basal tooth; gastral pilosity usually appearing somewhat dense, with setae subdecumbent to decumbent and not obviously bilayered, but sometimes more clearly bilayered, with subdecumbent setae becoming suberect; head completely sculptured, mostly rugoreticulate; mesosoma usually mostly sculptured with rugae and punctate, but pronotum sometimes with sculpture largely effaced; petiole of moderate length, somewhat robust; eye relatively small (EL 0.07-0.12, REL 12-17), subcircular to oval-shaped, with 4-6 ommatidia at greatest diameter; propodeal spines tuberculate (PSL 0.07-0.14, PSI 1.0-1.4). Similar species: Stenamma catracho , Stenamma manni .

Geographic range.

Southern Mexico to Honduras.

Worker description.

(20 measured) HL 0.63-0.83 (0.71), HW 0.54-0.73 (0.60), FLD 0.14-0.20 (0.15), PCW 0.02-0.03 (0.02), SL 0.47-0.69 (0.55), EL 0.07-0.12 (0.08), ACL 0.48-0.66 (0.56), ML 0.76-1.09 (0.86), PrW 0.37-0.50 (0.41), PSL 0.07-0.14 (0.10), SDL 0.06-0.10 (0.08), PL 0.28-0.41 (0.33), PH 0.16-0.22 (0.18), PW 0.13-0.18 (0.14), PPL 0.14-0.21 (0.16), PPH 0.14-0.20 (0.16), PPW 0.16-0.22 (0.17), MFL 0.51-0.77 (0.60), MTL 0.43-0.63 (0.50), CI 83-88 (85), SI 82-95 (92), REL 12-17 (13), FLI 25-31 (26), PSI 1.0-1.4 (1.2), MFI 94-110 (100), ACI1 65-70 (69), ACI2 92-104 (101).

Small- to medium-sized species; general body color mostly dark red-brown (almost black) to orange-brown, with head and pronotum darker, and gaster with lighter patches of brown; appendages mostly a uniform and distinctly lighter orange-brown to yellow-brown; setae golden brown; mandible usually with 6-7 teeth (usually 6), but sometimes with 1-3 additional small denticles, middle 2-3 teeth nearest basal tooth often worn and indistinct; basal margin of mandible usually sinuous (rarely straight), with a shallow to very deep basal depression, but without a basal tooth; mandible mostly smooth and shining, with scattered piligerous punctae and striae (mostly on lateral side); anterior clypeal margin usually with 4 sharp to blunt teeth, outer teeth often larger and sharper, sometimes teeth reduced (especially inner two teeth), almost absent, and clypeal margin strongly emarginate; median clypeal lobe with a pair of very faint longitudinal carinulae, and a short transverse carinula near apex, remainder of clypeus smooth and shiny; posterior extension of the clypeus between the antennal insertions narrow (PCW 0.02-0.03), with sides subparallel; frontal lobes usually of moderate width, but somewhat expanded in Cusuco population (FLD 0.14-0.20, FLI 25-31); torular lobes not completely covered in full-face view; frontal carinae blending into head sculpture, not extending beyond about midpoint level of eye; head subrectangular to oval-shaped (CI 83-88), with posterior margin flat to slightly depressed medially; face mostly rugoreticulate, with a few longitudinal rugae along the midline, sometimes sculpture more polished and posterior quarter of head becoming smooth and shiny, interstices faintly punctate; scape of moderate length (SI 82-95), usually not reaching posterior margin in full-face view; scape surface mostly smooth and shiny, with scattered piligerous punctae; funiculus with a somewhat distinct 4-segmented antennal club (ACI2 65-70); pronotum sculpture varying from nearly completely smooth and shiny to strongly rugose (dorsum) and punctate or rugulose (side), with rugae mostly longitudinal in orientation; mesopleuron and propodeal side mostly punctate, with a few rugulae; propodeal dorsum and declivity (to a lesser degree) with punctae and transverse carinulae; promesonotum in profile low-domed, roughly symmetrical; location of promesonotal suture obscured to well-defined, depending on degree of pronotal sculpturing; metanotal grove well-demarcated, of moderate width and depth; propodeal spines tuberculate (PSL 0.07-0.14, PSI 1.0-1.4); petiole of average length (PL/HW 0.51-0.57); petiolar node of moderate to small size (PH/PL 0.53-0.62) and variable in shape, being either wedge shaped and strongly asymmetrical, or subconical, with the apex gently rounded and pointing only slightly posteriad; postpetiole in profile average-looking, about the same size as petiolar node (PPH/PH 0.83-0.96); anterior faces of petiolar nodes smooth and shiny, remaining surfaces of waist mostly punctate, with a few rugulae around nodes; gaster mostly smooth and shiny, with scattered piligerous punctate and a ring of short striae around the anterior constriction; most of body dorsum with somewhat short standing pilosity; scape decumbent to appressed; gastral pilosity variable, usually appearing somewhat dense, with setae subdecumbent to decumbent and not obviously bilayered, but sometimes more clearly bilayered, with subdecumbent setae becoming suberect; setae on legs decumbent to appressed, with suberect to subdecumbent setae on coxae and profemur venter.

Queen description.

(5 measured) HL 0.72-0.85 (0.75), HW 0.65-0.76 (0.67), FLD 0.17-0.21 (0.17), PCW 0.03-0.05 (0.05), SL 0.53-0.66 (0.59), EL 0.17-0.20 (0.17), ACL 0.55-0.62 (0.57), ML 1.01-1.26 (1.06), PrW 0.55-0.73 (0.57), PSL 0.13-0.17 (0.15), SDL 0.08-0.12 (0.10), PL 0.37-0.48 (0.39), PH 0.20-0.25 (0.21), PW 0.17-0.22 (0.18), PPL 0.18-0.22 (0.19), PPH 0.19-0.26 (0.20), PPW 0.21- 0.29 (0.22), MFL 0.60-0.80 (0.65), MTL 0.53-0.69 (0.56), CI 88-90 (90), SI 82-89 (88), REL 25-28 (25), FLI 26 –– 28 (26), PSI 1.5-1.7 (1.5), MFI 95-107 (103), ACI1 64-68 (67), ACI2 93-106 (96).

Same as worker except for standard queen modifications and as follows: pronotum transversely rugose laterad, becoming smooth mesad; mesoscutum ranging from mostly smooth, with some faint foveolae, to mostly carinulate/rugose (strength of sculpture correlates with pronotum sculpture of worker); scutellum longitudinally rugose, often with a central patch of smooth cuticle; most of katepisternum and sometimes lower half of anepisternum smooth; propodeal spines slightly more developed; setae on mesoscutum subdecumbent to appressed, more dense; pilosity in general slightly more dense; wing venation in Figure 135D.

Male.

Unknown.

Biology.

Stenamma ochrocnemis is known mostly from extracts of sifted leaf litter collected from the forest floor, but workers also have been found at cookie baits and once underneath a rock. The species is a high-elevation specialist occurring from approximately 1600-2750 m, with most collections around 2000 m. It inhabits wet montane forests, such as cloud forest, oak forest, hardwood forest, and mixed oak cloud forest.

Comments.

The most distinctive feature of this species is its light colored legs, which always make it stand out from other Stenamma species when sorting specimens in ethanol. Stenamma ochrocnemis appears superficially similar to several other MAC species, but it should be separable by the characters listed in the diagnosis. Phylogenetic data show that Stenamma ochrocnemis belongs to a clade that includes Stenamma hojarasca and most likely Stenamma cusuco (Branstetter unpublished data).

Across its range there is significant variation in body size, surface sculpture, gastral pilosity and the configuration of the clypeus and basal margin of the mandible. I describe several variants here, but it should be noted that almost every population has some distinctive feature, making separation of this species into discrete forms somewhat arbitrary. In the type population (Figure 135), the body has a very dark red-brown color, the pronotum is strongly rugose, the basal margin of the mandible has a large deep depression, and the anterior clypeal margin forms several sharp teeth. This form is rather distinctive and seems to be restricted to localities in Honduras.

Variant 1 (Figure 135 A–C) differs from the type population in that it has the pronotum mostly to completely smooth and shiny, it has lighter body color, and the depression in the basal margin of the mandible is not as deep. This form occurs mainly in Chiapas, Mexico, and Guatemala. Variant 2 (Figure 135 D–F) is a slightly different version of variant 1 and it is known from the locality Huitepec in Chiapas, Mexico. Workers are noticeably larger, the propodeal spines are more developed, and the petiole appears elongate, with the node in profile more asymmetrical.

Variant 3 (Figure 135 G–I) occurs mainly at the locality 5km SE Antigua in Guatemala, with similar forms at nearby sites. It has the pronotum mostly sculptured, it has lighter orange-brown body color, and it has the basal margin of the mandible only slightly sinuous, almost without a basal depression. Interestingly, this variant co-occurs with variant 1-like specimens (Figure 135 J–L) at the Antigua site, suggesting that there may be reproductive isolation between the two forms. I have noticed some ecological differences, with the more sculptured form occurring at slightly lower elevation and in more disturbed habitat than the less sculptured form. Molecular data, however, suggest there is only one species. I have sampled one specimen of each form from the Antigua site, and these are inferred to be sister to each other and nested within the larger Stenamma ochrocnemis complex. This result shows that the specimens they are not grouping by sculpture type, but by locality. Additional evidence indicating the existence of only one species is that, specimens with intermediate phenotypes occur at other sites in Guatemala. Thus, I treat this variation as intraspecific.

Variant 4 (Figure 135 M–O) is known only from a few specimens collected at Cusuco in Honduras. It is similar to variant 1, except that it has the frontal lobes somewhat dorsolaterally expanded. The form of the frontal lobes is very similar to Stenamma cusuco or Stenamma hojarasca , which both occur at Cusuco and have strongly expanded frontal lobes. This similarity is either an indication of a shared selection pressure, or perhaps some level of hybridization among species.

I include the specimens from Guerrero, Mexico, in Stenamma ochrocnemis with uncertainty. They represent the only collection of the species north of Chiapas, Mexico. Superficially they appear like variant 1, but there are some differences in sculpture and petiole shape, and it is difficult to interpret body and leg color because the specimens are old and faded. Until more material can be collected, I treat this record as dubious.

From the variation described above, there does seem to be a geographic pattern, in which specimens with a smooth pronotum occur in Chiapas, Mexico, both sculptured and unsculptured forms occur in Guatemala, and then mainly sculptured forms occur in Honduras. The degree of reproductive isolation of the different forms/populations is unclear and would be interesting to study. This pattern of morphological variation is similar to that seen in the Stenamma maximon complex (see comments section for Stenamma maximon above).

Material examined.

GUATEMALA: El Progresso: Cerro Pinalón, Finca Las Nubes, 15.07724°N, 89.94785°W, 2350m, 21 Sep 2008 (R. S. Anderson);Huehuetenango: 3.3km WSW El Paraíso, 15.53697°N, 91.98158°W, 2350m, 16 Sep 2008 (M. G. Branstetter); San Miguel Chicharro, 4km NNW El Paraíso, 15.57958°N, 91.96916°W, 2100m, 16 Sep 2008 (M. G. Branstetter); Jalapa: 4km E Mataquescuintla, 14.53320°N, 90.15298°W, 2400m, 1 Jun 2009 (LLAMA); Miramundo, Pino Dulce, 14.53388°N, 90.15236°W, 2300m, 18 Sep 2008 (R. S. Anderson);Quetzaltenango: 2.9km SSE Chichicastenango, 14.91861°N, 91.10449°W, 2000m, 17 Sep 2008 (M. G. Branstetter); Sacatepéquez: 5km SE Antigua, 14.54155°N, 90.71138°W, 1715m, 12 Jun 2009 (LLAMA); 5km SE Antigua, 14.53666°N, 90.66491°W, 2150m, 10 Jun 2009 (LLAMA); 5km SE Antigua, 14.52799°N, 90.68945°W, 2350m, 10 Jun 2009 (LLAMA); Cerro Alux, 14.61053°N, 90.64191°W, 2190m, 9 Sep 2008 (R. S. Anderson); Cerro Alux, Guatemala City, [ca. 14.6167°N, 90.6333°W], 2260m, 9 Jun 1991 (R. S. Anderson); Cerro Carmona, Finca El Pilar, 14.54115°N, 90.70483°W, 1980m, 9 Sep 2008 (R. S. Anderson); Suchitepéquez: 4km S Vol. Atitlán, 14.54867°N, 91.19089°W, 1625m, 15 Jun 2009 (LLAMA); 4km S Vol. Atitlán, 14.55279°N, 91.19317°W, 1750m, 15 Jun 2009 (LLAMA); HONDURAS:Comayagua: 10km ENE Comayagua, 14.45982°N, 87.54564°W, 2000m, 15 May 2010 (LLAMA); 12km ENE Comayagua, 14.48032°N, 87.53240°W, 2140m, 15 May 2010 (LLAMA); 12km ENE Comayagua, 14.48418°N, 87.52934°W, 2270m, 16 May 2010 (LLAMA); Cortés: PN Cusuco, 15.50739°N, 88.23373°W, 2030m, 3 Jun 2010 (LLAMA); Ocotepeque: 13km E Nueva Ocotepeque, 14.45788°N, 89.06812°W, 2190m, 25 May 2010 (LLAMA) 13km E Nueva Ocotepeque, 14.41971°N, 89.06937°W, 2190m, 26 May 2010 (LLAMA); 13km E Nueva Ocotepeque, 14.4224°N, 89.0608°W, 2160m, 26 May 2010 (LLAMA); MÉXICO: Chiapas: Cerro Huitepec (Pico), ca. 5km W San Cristobal, [ca. 16.7500°N, 92.6802°W], 2750m, 18 Sep 1991 (R. S. Anderson); 5km NE Coapilla, 17.17071°N, 93.13677°W, 1970m, 27 May 2008 (R. S. Anderson); 2km SE Custepec, 15.72216°N, 92.94298°W, 1820m, 20 May 2008 (R. S. Anderson); 4km SE Custepec, 15.7119°N, 92.92840°W, 2140m, 20 May 2008 (LLAMA); 4km SE Custepec, 15.70777°N, 92.93110°W, 2125m, 20 May 2008 (LLAMA); Huitepec, S. Cristóbal, 16.75149°N, 92.68270°W, 2480m, 29 May 2008 (LLAMA); 7.4km SSW Motozintla de Mendoza, [ca. 15.367°N, 92.233°W], 2000m, 21 Sep 1992 (R. S. Anderson); 7km WSW San Cristóbal, 16.7205°N, 92.7012°W, 2400m, 9 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); Guerrero: 5.6km SW Filo de Caballo, [ca. 17.6212°N, 99.7469°W], 2310m, 13 Jul 1992 (R. S. Anderson). Nicaragua:Nueva Segovia: Cerro Mogotón, 10km NNE Mozonte, 13.75599°N, 86.42062°W, 2010m, 24 Apr 2011 (M. G. Branstetter); 14km NNE Ocotal, 13.75409°N, 86.42094°W, 1900m, 24 Apr 2011 (R. S. Anderson).