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Species: Stenamma crypticum   Branstetter, 2013 

Classification:
Download Data

Taxonomic History (provided by Barry Bolton, 2021)

Stenamma crypticum Branstetter, 2013 PDF: 80, figs. 68-71 (w.q.) MEXICO. Neotropic. AntCat AntWiki

Overview:

This species belongs to the Middle American clade of Stenamma (see Branstetter 2012). All conent on this page modified from Branstetter (2013) unless noted otherwise.

// Distribution

Distribution:

  Geographic regions (According to curated Geolocale/Taxon lists):
    Americas: Guatemala, Honduras, Mexico, Nicaragua
  Biogeographic regions (According to curated Bioregion/Taxon lists):
    Neotropical

Distribution Notes:

Southern Mexico (Chiapas, Veracruz?) to Honduras.

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.

Identification:

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, S. huachucanum, S. ignotum, S. picopicucha.

     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 specimen CASENT0605933
     Male. Unknown.

Comments:

This taxon was previously known by the morphospecies codes mgb12, mgb13, and mgb17.

Stenamma crypticum should be distinguished easily from S. ignotum and S. picopicucha using the diagnostic characters given above. Separating S. crypticum from S. connectum and S. 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, Branstetter (2013) delimits 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 S. connectum is found north of S. 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 S. connectum and have a mostly smooth promesonotum. I tentatively identify these specimens as S. crypticum, but I find it possible that they could actually be abberant members of S. connectum, which has been collected close by at a slightly lower elevation (1400 m). The phylogenetic position of the putative S. 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 S. huachucanum occurs in eastern Mexico from Tamaulipas to Puebla.

Stenamma picopichuca can be separated from S. 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 S. ignotum and the anterior clypeal margin like S. crypticum. Because of several other similarities, Branstetter (2013) was originally going to include S. picopicucha in S. crypticum, but later discovered that the two species occur in sympatry at Cusuco in Honduras. At this site, specimens of S. crypticum clearly have a sinuous basal margin of the mandible and specimens of S. picopicucha have a straight margin. The phylogenetic position of S. picopicucha is yet to be tested, and it will be interesting to see if the two species are closely related.

Within the range of S. 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, S. crypticum has been sampled 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 (CASENT0603821), and others mostly rugose (CASENT0604745). At first Branstetter (2013) tried separating these into distinct forms, but the scheme was abandoned 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 Branstetter (2013) describes a couple of variants. Variant 1 (CASENT0604839) occurs at several sites in Guatemala (e.g. Biotopo Quetzal, Purulhá). It is similar to the type form (CASENT0604771), but has a bulging postpetiole and longer gastral pilosity. Variant 2 (CASENT0604997) 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. Without evidence of sympatry, Branstetter (2013) treats all of this variation as intraspecific.

The specific epithet crypticum refers to the cryptic nature of this species.

Taxonomic Notes:

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].

References:

Branstetter, M. G. 2012. Origin and diversification of the cryptic ant genus Stenamma Westwood (Hymenoptera: Formicidae), inferred from multilocus molecular data, biogeography and natural history. Systematic Entomology 37:478-496. 10.1111/j.1365-3113.2012.00624.x.

Branstetter, M. G. 2013. Revision of the Middle American clade of the ant genus Stenamma Westwood (Hymenoptera, Formicidae, Myrmicinae). ZooKeys 295:1-277. doi: 10.3897/zookeys.295.4905.

Specimen Habitat Summary

Found most commonly in these habitats: 264 times found in cloud forest, 113 times found in 2º mesophil forest, 38 times found in mesophil forest, 3 times found in bosque nuboso, 3 times found in oak forest, 4 times found in ridge oak forest litter, 4 times found in mixed hardwood forest litter, 4 times found in oak forest litter, 3 times found in montaine wet forest, 3 times found in disturbed cloud forest, ...

Found most commonly in these microhabitats: 451 times ex sifted leaf litter, 30 times at bait, 10 times forest litter, 4 times leaf litter, 1 times sifted litter (leaf mold, rotten wood), 1 times ex leaf litter.

Collected most commonly using these methods: 334 times MiniWinkler, 37 times Berlese/Winkler, 52 times maxiWinkler, 28 times Berlese, 13 times Winkler, 29 times Baiting, 3 times Night MiniWinkler, 1 times bait.

Elevations: collected from 50 - 2750 meters, 1850 meters average

Collect Date Range: collected between 1950-08-01 and 2011-05-12

Type specimens: Holotype Stenamma crypticum: casent0604771



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