Stenamma connectum, 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 : 54-61

Stenamma connectum sp. n. Worker: Figures 64, 65; Queen: Figure 66; Male: Figure 66 E–G; Map: Figure 67

Type material.

Holotype worker. MÉXICO, Oaxaca: 10.8km SW Valle Nacional, 17.68102°N, 96.33026°W ± 66m, 1120m, 13 Aug 2009, disturbed mesophyll forest, ex sifted leaf litter (M. G. Branstetter, collection MGB1387) [USNM, specimen CASENT0622438]. Paratypes: same data as holotype [1dq, 1w, CAS, CASENT0623275, CASENT0623261], [1w, EAPZ, CASENT0623262], [1w, ECOSCE, CASENT0623263], [1w, FMNH, CASENT0623264], [1w, ICN, CASENT0623265], [1w, INBio, CASENT0623266], [1w, JTLC, CASENT0623274], [1w, LACM, CASENT0623267], [1w, MGBPC, CASENT0623268], [1dq, 1w, MCZ, CASENT0623276, CASENT0623272], [1w, MZSP, CASENT0623269], [1w, UCD, CASENT0623270], [1w, UNAM, CASENT0623271], [1dq, 1w, USNM, CASENT0622439, CASENT0623260], [1w, UVGC, CASENT0623273].

Worker diagnosis.

Integument mostly dark brown to brown, rarely black; small-sized species (see HL, ML, PrW below); basal margin of mandible sinuous, with a distinct basal depression; anterior clypeal margin undulating, forming 2-4 blunt teeth; face completely sculptured, mostly rugoreticulate; mesosoma mostly sculptured, except for pronotum, which is usually lightly carinulate-punctate, with a small smooth patch on dorsum and side, but sometimes pronotum completely punctate or mostly smooth; remainder of mesosoma usually strongly punctate; propodeal declivity in profile usually with distinctive outline, in which propodeal lobe is broadly rounded and makes a smooth, sinuous connection with propodeal spine (degree of sinuosity variable); eye of small to moderate size (EL 0.07-0.11, REL 15-19), oval-shaped, with 4-5 ommatidia at greatest diameter; pilosity on gastral dorsum bilayered, with a layer of longer suberect setae, and a denser layer of decumbent setae; propodeal spines tuberculate, or reduced to sharp angles (PSL 0.07-0.09, PSI 1.1-1.4); geography useful in species determination. Similar species: Stenamma crypticum , Stenamma huachucanum .

Geographic range.

Southern Mexico (Oaxaca, Veracruz).

Worker description.

(20 measured) HL 0.52-0.69 (0.54), HW 0.45-0.60 (0.48), FLD 0.11-0.16 (0.12), PCW 0.02-0.04 (0.02), SL 0.39-0.58 (0.42), EL 0.07-0.11 (0.08), ACL 0.40-0.54 (0.43), ML 0.61-0.87 (0.65), PrW 0.31-0.40 (0.32), PSL 0.07-0.09 (0.08), SDL 0.05-0.07 (0.06), PL 0.22-0.32 (0.23), PH 0.14-0.19 (0.14), PW 0.10-0.16 (0.11), PPL 0.12-0.20 (0.14), PPH 0.12-0.19 (0.13), PPW 0.13-0.19 (0.15), MFL 0.38-0.62 (0.44), MTL 0.31-0.52 (0.35), CI 84-92 (89), SI 85-99 (87), REL 15-19 (16), FLI 24-28 (25), PSI 1.1-1.4 (1.4), MFI 96-117 (109), ACI1 67-72 (70), ACI2 93-105 (102).

Small-sized species; general body color usually dark brown to brown, rarely almost black; appendages brown to yellow-brown, becoming lighter toward extremities; in specimens with dark brown to black body color, flagellum sometimes noticeably bright yellow; setae golden brown; mandible with 6 teeth, with basal tooth well defined; basal margin of mandible sinuous, with a distinct basal depression; mandible surface mostly smooth and shiny, with scattered piligerous punctae, and some striations on base and lateral surface; anterior clypeal margin undulating, forming 2-4 blunt teeth, inner teeth often projecting beyond lateral teeth (type population); median lobe of clypeus with a pair of longitudinal carinulae that diverge anteriorly, apex of lobe with a moderately long transverse carinula, area in between median lobe and anterior margin forming a distinct cavity where mandibles insert, remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions of moderate to somewhat narrow width (PCW 0.02-0.04), with sides subparallel to slightly hour-glass shaped; frontal lobes of moderate width (FLD 0.11-0.16, FLI 24-28), not greatly obscuring torular lobes in full-face view; head roughly oval-shaped (CI 84-92), posterior margin with a slight to distinct median depression; eye of small to moderate size (EL 0.07-0.11, REL 15-19), oval-shaped, with 4-5 ommatidia at greatest diameter; face completely sculptured, mostly rugoreticulate, with some longitudinal carinulae extending back from frontal lobes, interstitial areas with light piligerous punctae; one high-elevation population with facial sculpture more polished, becoming smooth toward posterior margin; scape somewhat short (SI 85-99), not reaching posterior margin when laid back; scape surface mostly smooth, with scattered piligerous punctae; flagellum with a distinct 4-segmented antennal club; mesosoma mostly sculptured, except for pronotum, which ranges from completely punctate to almost completely smooth (both extremes rare); pronotum most often lightly punctate on side, and lightly carinulate-punctate on dorsum, with a small smooth patch in middle (type population); remainder of mesosoma mostly punctate, with some longitudinal carinulae, becoming rugoreticulae on mesonotum; propodeal dorsum and declivity sometimes with transverse carinulae; one high-elevation population with mesopleuron rugulose-punctate, and side of propodeum longitudinally carinulate; promesonotum in profile low-domed and roughly symmetrical; metanotal groove well demarcated, of moderate width and depth; propodeum in profile usually with a distinct profile, in which propodeal lobe has a broadly rounded margin that connects smoothly with propodeal spine; connection usually sinuous, but degree of sinuosity variable; propodeal spines usually tuberculate (type population), but sometimes reduced to sharp angles (PSL 0.07-0.09, PSI 1.1-1.4); petiole in profile of moderate length to slightly elongate (PL/HW 0.49-0.55); petiolar node in profile appearing small (PH/PL 0.52-0.64), and asymmetrical, with anterior face longer and more sloping than posterior face, node dorsum broadly rounded (type population) to more angulate, with apex pointing distinctly posteriad; postpetiole in profile subspherical, usually about same size as petiolar node, but sometimes slighly bulging (PPH/PH 0.79-1.01); petiole and postpetiole usually mostly punctate, with only anterior faces smooth and shiny, but sometimes nodes almost completely smooth; most of body dorsum with short standing pilosity; setae on face very short, mostly subdecumbent; pilosity on gastral dorsum bilayered, with a sparse layer of longer suberect setae, and a denser layer of decumbent setae, sometimes lower layer very similar in density to upper layer; setae on scape subdecumbent to appressed; setae on legs mostly decumbent to appressed, with some suberect setae on femoral venters and coxae.

Queen description.

(8 meausred) HL 0.55-0.68 (0.56), HW 0.50-0.62 (0.51), FLD 0.13-0.15 (0.13), PCW 0.03-0.05 (0.03), SL 0.42-0.56 (0.45), EL 0.14-0.17 (0.15), ACL 0.43-0.52 (0.45), ML 0.74-1.00 (0.78), PrW 0.44-0.55 (0.46), PSL 0.09-0.11 (0.11), SDL 0.07-0.09 (0.09), PL 0.28-0.36 (0.29), PH 0.16-0.21 (0.16), PW 0.12-0.17 (0.13), PPL 0.14-0.21 (0.15), PPH 0.16-0.21 (0.16), PPW 0.17-0.22 (0.17), MFL 0.44-0.62 (0.46), MTL 0.38-0.53 (0.39), CI 88-93 (91), SI 83-95 (88), REL 27-30 (29), FLI 25-26 (26), PSI 1.2-1.5 (1.3), MFI 96-115 (111), ACI1 66-69 (68), ACI2 93-106 (102).

Same as worker except for standard queen modifications and as follows (comparsion of type population only): pronotum with transverse carinulae/rugulae; mesoscutum mostly smooth, with piligerous punctae, and some longidutinal carinulae along lateral margin; scutellum smooth in middle, rugulose-punctate on lateral margins; mesopleuron mostly smooth; propodeum carinulate-punctate; lower layer of setae on gastral dorsum very dense, almost pubescent; dorsum of mesosoma and anterior faces of petiolar and postpetiolar nodes with a dense layer of short, decumbent setae; propodeal declivity in profile less sinuous, with propodeal lobe smaller and less evenly rounded; wing venation as in Figure 66D.

Male.

See Figure 66 E–G.

Biology.

Stenamma connectum is found in montane wet forest habitats from 600-2160 m elevation, and is known almost exclusively from Winkler or Berlese samples of sifted leaf litter. Only once has a nest been found: a single dealate queen with brood underneath a moss mat.

Comments.

Distinguishing Stenamma connectum from Stenamma crypticum and Stenamma huachucanum can be difficult. This is because each species is composed of multiple allopatric populations with no clear evidence of sympatry among divergent forms. Using morphology alone, the best solution would probably be to delimit a single widespread species. However, molecular phylogenetic data strongly suggest the existence of multiple biological species (Branstetter unpublished data). As a result, I have decided to delimit several species guided by the combination of morphological and molecular data. Some phenotypically divergent populations which have not been included in the phylogeny may prove challenging to identify.

As currently defined, geography is very useful in separating Stenamma connectum from similar species. Stenamma connectum occurs in the Mexican states of Veracruz and Oaxaca only. Within Oaxaca, it is found along the Caribbean slope in wet forest habitats. Stenamma huachucanum is distributed from the southwestern U.S.A to Oaxaca. Within Oaxaca, it occurs only in the drier habitats in the central and western parts of the state. I consider specimens from Hidalgo and San Luis Potosí states to be Stenamma huachucanum , but some of these specimens are hard to place. Stenamma crypticum occurs mainly from Chiapas, Mexico to Nicaragua; however, a couple of specimens known from one sample collected in Veracruz at 1600 m (11km N San Andrés Tuxtla) appear most like Stenamma crypticum . These specimens lack the broadly rounded propodeal lobes (in profile) and have the promesonotum mostly smooth. Until more material is collected, I treat these as Stenamma crypticum , but I find it possible that they are actually abberant specimens of Stenamma connectum. One specimen that clearly has the characteristics of Stenamma connectum was collected at nearly the same locality, only slightly lower at 1400 m elevation.

Many populations of Stenamma connectum , including the type population, share a set of distinctive morphological character states that distinguish Stenamma connectum from similar species. Key worker characters for the type population are as follows: body color mostly brown; side of pronotum lightly punctate; dorsum of pronotum carinulate-punctate with a small patch of smooth cuticle in middle; mesopleuron and side of propodeum strongly punctate; propodeal declivity in profile forming a sinuous outline, in which the propodeal lobe is broadly rounded and makes a smooth connection with the propodeal spine; propodeal spines tuberculate. The sinuous outline of the propodeal declivity is the most distinctive feature of this species. It is variable among populations, with specimens from lower elevations having the sinuosity more pronounced. Higher elevation populations begin to lose the character state, making these populations more difficult to separate from similar species. Several variants are described below.

Variant 1 (Figure 65 A–C) is known only from the locality Pueblo Nuevo in Veracruz. These specimens differ as follows: smaller overall size; mesosoma completely punctate, with only a few scattered rugulae/carinulae; sinuosity in outline of propodeal declivity pronounced; petiolar node in profile reaching a more angular apex.

Variant 2 (Figure 65 D–F) and variant 3 (Figure 65G-I) occur along the same elevational transect as the type population, but at mid (~1770 m) and high (> 1900 m) elevations, respectively. Variant 2 differs from the type form in that it has dark brown body color, reduced pronotal sculpture, and a noticeably yellow flagellum. Variant 3 is a high elevation form of Stenamma connectum . Without the intermediate phenotype present in variant 2, it would be easy to describe variant 3 as a new species as it is very divergent from the type population. It is similar to variant 2 except as follows: larger size; body color almost black; pronotum almost completely smooth and shiny; mesopleuron rugulose-punctate; side of propodeum carinulate; outline of propodeal declivity not strongly sinuous, with the propodeal lobe often more angular and isolated from the propodeal spine; petiolar and postpetiolar nodes mostly smooth; postpetiole bulging.

Material examined.

MÉXICO: Oaxaca: Mirador Grande, 17.89844°N, 96.36263°W, 990m, 14 Aug 2009 (M. G. Branstetter); 10km S Valle Nacional, [ca. 17.724°N, 96.324°W], 650m, 19 May 1971 (S. B. Peck); 10.8 km 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); 14.8km SSW Valle Nacional, 17.64483°N, 96.33637°W, 1370m, 13 Aug 2009 (M. G. Branstetter); 20.5km SW Valle Nacional, 17.60560°N, 96.38398°W, 1770m, 12 Aug 2009 (M. G. Branstetter); 20.6km SW Valle Nacional, 17.60404°N, 96.378786°W, 1733m, 13 Aug 2009 (M. G. Branstetter); 22.4km SW Valle Nacional, 17.59112°N, 96.39133°W, 1990m, 13 Aug 2009 (M. G. Branstetter); 25km S Valle Nacional, [ca. 17.670°N, 96.330°W], 1200m, 21 May 1971 (S. B. Peck); 26km SW Valle Nacional, 17.58667°N, 96.44948°W, 2160m, 11 Aug 2009 (M. G. Branstetter); 30.1km S Valle Nacional, [ca. 17.627°N, 96.354°W], 1580m, 11-18 Aug 1973 (A. F. Newton); 47.5km SW Valle Nacional, Km 100.5, [ca. 17.595°N, 96.424°W], 2125m, 26 Jul 1992 (R. S. Anderson); 52km S Valle Nacional, [ca. 17.587°N, 96.449°W], 2130m, 22 May 1971 (S. B. Peck); Veracruz: Cordoba, [ca. 18.908°N, 96.958°W], 4 Aug 1969 (S. B. Peck); Cordoba, Paraje Nuevo, Nacimiento, [ca. 18.88°N, 96.86°W], 7 Aug 1969 (S. & J. Peck); park cañon, Hwy150, 3.2km W Fortín, [ca. 18.884°N, 97.019°W, 6-9 Aug 1969 (S. & J. Peck); Fortín, Canyon Río Metlac, [ca. 18.90°N, 97.00°W], 5 Aug 1969 (S. & J. Peck); 7km E Huatusco, [ca. 19.207°N, 96.914°W], 22 Jun 1983 (Peck & Anderson); 7.1km N Huatusco, [ca. 19.262°N, 96.964°W], 1280m, 29 Jul– 3 Aug 1973 (A. F. Newton); Paraje Nuevo, Cueva de Ojo de Agua, [ca. 18.877°N, 96.862°W], 7 Aug 1969 (S. & J. Peck) Pueblo Nuevo, nr Tetzonapa, 1 Aug 1953 (E. O. Wilson); 11km N San Andrés Tuxtla, 18.55°N, 96.00°W, 1400m, 23 Mar 1985 (P. S. Ward); 2.7km N Teocelo, [ca. 19.40°N, 96.98°W], 1130m, 22-24 Jul 1934 (A. F. Newton).